Land-Based Carbon Effects and Human Well-Being Nexus

Abstract

In light of international climate agreements and the Sustainable Development Goals (SDGs), there is a growing need to enhance the understanding of the linkages among land use/cover change (LUCC) and its carbon effects (CEs), as well as human well-being (HW). While existing studies have primarily focused on the impacts of LUCC on CEs or ecosystem services, there remains a gap in systematically elucidating the complex relationships among LUCC, CEs, and HW. This paper presents a comprehensive review of the nexus between land-based CEs and HW, examining: (1) the correlation between LUCC and CEs, encompassing methodologies for investigating LUCC CEs; (2) the association between CEs and HW, introducing the concept of “low-carbon human well-being” and evaluation framework; and (3) the proposed framework of “LUCC-CEs-HW,” which delves into the intricate connections among three elements. The study identifies research gaps and outlines potential future directions, including assessments of LUCC CEs and low-carbon HW, exploration of the “LUCC-CEs-HW” nexus, and the development of standardized measurement approaches. Key opportunities for further investigation include establishing a unified evaluation index system and developing scalable methods. This paper elucidates the relationships among LUCC, CEs, and HW, offering insights for future works.

1. Introduction

The Paris Agreement established a global target to limit the increase in average temperature to below 2 °C above pre-industrial levels, with an additional goal of capping the increase at 1.5 °C and achieving “net-zero emissions” by the latter half of the current century [1]. This necessitates an equilibrium between human-induced greenhouse gas emissions and their removal. Nations worldwide have intensified monitoring efforts on carbon emissions and sequestration. Land use and land cover change (LUCC) resulting from human activities, notably deforestation and the conversion of agricultural areas to urban spaces, have diminished carbon sequestration zones while expanding carbon emission sources. A focus on the carbon impacts of LUCC is crucial for achieving carbon neutrality.

In 2012, a collaborative effort between the International Council for Science, the International Council for Social Sciences, and other organizations resulted in the initiation of a decade-long (2014–2023) global research program called “Future Earth” [2]. This program was officially launched during the United Nations Conference on Sustainable Development and focused on three primary research themes: Dynamic Earth, Global Development, and Transition to Sustainable Development. In 2015, the United Nations introduced 17 Sustainable Development Goals (SDGs) aimed at addressing critical challenges confronting humanity, including climate change, poverty, inequality, and quality education [3]. As shown in Figure 1, the majority of SDG indicators are directly or indirectly linked to human well-being (HW). While certain goals such as clean water and sanitation, sustainable cities and communities, and responsible consumption and production are closely tied to carbon impacts, a significant portion of the objectives are interconnected with LUCC and HW. Scholars from diverse nations have been actively involved in extensive research efforts to align the goals of sustainable development with the improvement of HW in light of the Future Earth initiative and the SDGs.

In light of the increasing problem of global warming and significant human-induced LUCC, it is essential to integrate carbon considerations into the LUCC and HW framework to support sustainable development and improve HW. As LUCC is a major terrestrial carbon source, its carbon impacts are vital for achieving the goals set by the “Future Earth” initiative and SDGs. Therefore, exploring the linkages among LUCC, carbon effects, and HW is highly significant.

Land use involves planning, developing, and using land resources for economic, social, and ecological benefits, focusing on societal and economic contributions. Land cover refers to the physical characteristics of the Earth’s surface, including biota, soil, water bodies, and human-made structures. While distinct, land use and land cover are interconnected and often studied together as part of the LUCC system. LUCC, reflecting human activities, significantly influences the carbon cycle in terrestrial ecosystems, contributing about 14% of global carbon emissions between 2009 and 2014, ranking second to fossil fuel combustion [5]. Research on land use’s impact on carbon emissions has increased since the 1990s.

Numerous research studies have investigated the impact of LUCC on carbon emissions, the correlation between energy sequestration and carbon release, strategies for optimizing land use to reduce carbon emissions, and the potential risks of carbon emissions associated with land use practices at various scales [6,7]. Some studies have focused on carbon emissions resulting from specific land use changes. For example, Qin et al. revealed that forest degradation in the Brazilian Amazon leads to greater carbon loss than deforestation [8]. Other research has used simulations to evaluate how different land use practices affect annual variations in land carbon balance, aiming to leverage land use management to combat climate change.

Wang and colleagues found that LUCC can affect carbon emissions and regional ecosystem services, consequently impacting HW [9]. Research mainly focuses on the correlation between ecosystem services, carbon emissions, and land use decisions. Tang et al. studied the changes in ecosystem service value and land carbon release risk in Gaoyang County, Baoding City, and Hebei Province [10]. Similarly, Chen et al. analyzed the spatio-temporal variations in carbon emissions and ecosystem values due to LUCC in urban areas in Chengdu and Chongqing, China [11].

Numerous studies have been dedicated to investigating the long-term impacts of LUCC on carbon dynamics within specific regions. These works involve assessing historical carbon emissions and projecting future trends. For instance, Hastie et al. examined the alterations in carbon storage resulting from LUCC activities in tropical peatlands within Peruvian forests between 2000 and 2016 [12]. In a similar vein, Liu et al. conducted a study on the dynamics of land use and land cover changes and their impact on carbon storage on Hainan Island from 1992 to 2019 [13]. Li et al. utilized the FLUS and InVEST models to simulate land use patterns and changes in carbon sequestration resulting from LUCC [14]. Furthermore, Zhu et al. investigated the relationship between land cover changes and carbon emissions. They identified the conversion of cultivated land to construction land as a predominant change in Shandong Province from 2000 to 2020, coinciding with an increase in land use intensity [15]. Yu et al. developed a novel LUCC database for China and conducted simulations using a land ecosystem model. The study revealed a significant expansion of forests between 1980 and 2019, which made a substantial contribution to the national terrestrial carbon sink [16]. Sha et al. proposed an integrated approach to determine optimal land management practices tailored to specific locations, estimating a potential additional carbon sequestration of 13.74 Pg C per year [17]. Marle et al. focused on the combined land–ocean carbon sink, observing a decreasing trend in the CO₂ airborne fraction and suggesting that the growth of land–ocean sinks may offset anthropogenic emissions [18]. Mishra et al. evaluated the impacts of the increasing demand for engineered wood on land use and associated carbon emissions using a land system simulation model [19]. Lastly, Beillouin et al. provided a comprehensive overview of meta-analyses on soil organic carbon (SOC), encompassing a wide range of original research conducted between 1910 and 2020 [20].

Previous studies on the link between carbon emissions and HW can be classified into four main groups. Researchers have used quantitative methods with open statistical data and survey responses. However, challenges in obtaining subjective data and the lack of comprehensive and precise data have impeded the development of a universally accepted research methodology for investigating this relationship. Generally, there is an observed trend of HW increasing along with carbon emissions, with decoupling mainly seen in more developed areas.

Li and Chen studied the link between carbon emissions and HW by focusing on energy release as a connecting factor [21]. They suggested that individual happiness depends on meeting needs, with energy dissipation playing a crucial role. Energy dissipation significantly contributes to carbon emissions. Understanding the relationship between energy dissipation and HW can shed light on the complex connection between carbon emissions and HW. Previous research has analyzed different aspects of HW in relation to carbon emissions. For example, Mazur and Rosa found a nonlinear relationship between social indicators (like health, education, and subjective well-being) and per capita energy dissipation across 55 countries [22]. Other studies have linked fundamental goods and services to levels of energy dissipation and carbon emissions. Rao and Wilson proposed studying the link between energy consumption and HW through consumption patterns [23]. Sileem and Al-Ayouty explored the carbon intensity of well-being in connection with factors such as gender equality, life expectancy, and gross domestic product [24]. Druckman and Jackson estimated greenhouse gas emissions from various household types in the UK based on minimum income standards [25]. The Human Development Index, a common measure of overall well-being, has been used to investigate the relationship between carbon emissions and HW. Research has shown different patterns of energy demand based on the Human Development Index in various countries, with a stronger correlation between quality of life and energy consumption in lower- to medium-developed countries compared to highly developed nations [26]. Studies in this field typically operate at international or national scales, albeit with some focus on community-level analyses. For example, Wang et al. developed a nonparametric evaluation model at the national level to identify inefficiencies in carbon emissions and propose policy interventions [27]. Lettenmeier et al. investigated the carbon footprint of low-income households in Finland to explore the feasibility of transitioning to a low-carbon lifestyle [28]. The intricate connections between carbon emissions and HW highlight the necessity for thorough research in this field, as carbon emissions can affect climate change and consequently impact HW. Balancing the imperative for enhanced HW with the necessity of curbing carbon emissions presents a multifaceted challenge that requires further exploration. The systematic examination of the trade-off between carbon emissions and HW has not been thoroughly investigated. Existing research focuses on the pairwise correlation between carbon effects and LUCC, or between HW and carbon effects. LUCC caused by human activities would affect carbon source and carbon sink effects. A study on LUCC, carbon effects, and HW as a whole has not yet appeared. The relationship between LUCC, carbon effects, and HW has not been systematically explained. The interaction of the three has not been defined. The interaction mechanism among the three has not been explained as a whole.

In the context of carbon neutrality and Sustainable Development Goals, for the purpose of narrowing the research gaps, this study aims to (1) introduce carbon into LUCC and the HW system; (2) raise a new framework of the nexus among LUCC, carbon effects, and HW to clarify the system more clearly; and (3) propose a low-carbon HW system.

2. Carbon Effects

The carbon effects can be classified into two categories: carbon sink and carbon source. Carbon sink refers to a process that usually entails the extraction of carbon dioxide from the atmosphere. Conversely, carbon source indicates a process that typically involves the emission of carbon dioxide into the atmosphere.

2.1. Carbon Sink Effect

Various research studies have examined various categories of carbon sinks, such as terrestrial ecosystem carbon sinks, forest system carbon sinks, SOC, and vegetation carbon sinks. By subdividing carbon sinks into more specific research units, a more precise and scientifically grounded understanding can be obtained regarding the impact of LUCC on carbon sinks [29].

Pu et al. provided a comprehensive overview of the methodologies employed for assessing the terrestrial ecosystem carbon sink in China, evaluating the strengths and weaknesses of each approach and outlining potential future directions [30]. As demonstrated in Figure 2, researchers investigate the processes of carbon sequestration in terrestrial ecosystems by using a combination of top-down and bottom-up research methodologies. The inventory method provides direct measurements of vegetation at a sample scale, which requires high-quality datasets. The vorticity correlation method is utilized to analyze the carbon cycle’s response to climate change at the ecosystem level. Although the ecosystem process simulation method is not exhaustive, it allows for quantitative differentiation of the contributions of various factors to changes in terrestrial carbon sinks and supports future predictions. The atmospheric inversion method relies on the accuracy and scope of data, facilitating real-time assessments of the functionality of terrestrial carbon sinks and their responsiveness to global climate changes.

In previous works, soil organic carbon research is particularly prevalent. Soil organic carbon refers to the buildup of organic materials in the soil, encompassing animal and plant remnants, microorganisms, as well as the byproducts of their decomposition and conversion processes. Within terrestrial ecosystems, the soil organic carbon reservoir stands as the most extensive carbon repository, representing approximately two-thirds of the overall carbon storage within terrestrial ecosystems.

LUCC exerts both direct and indirect influences on soil organic carbon storage [31]. LUCC directly alters ecosystem types, thereby affecting net primary productivity (NPP) and subsequent SOC inputs. Additionally, Zhou et al. noted that LUCC could potentially modify the physical and chemical properties of soil, altering soil’s respiration sensitivity to temperature changes [32]. Human activities, such as irrigation and nitrogen fertilizer application, can enhance soil respiration carbon flux under global warming conditions. As urbanization rates continue to rise, the carbon implications of LUCC, particularly driven by increased construction land, have garnered increased attention [33].

There is a growing body of research on SOC; however, these studies tend to focus on specific drivers of SOC changes and limited geographical regions. Research on the response of SOC to changes in land management practices or LUCC in countries with high SOC reserves is scarce [34]. Furthermore, there is a lack of studies conducted in Africa, which is particularly vulnerable to the impacts of climate change on rural activities. Fewer than 40 original studies have been carried out in more than 80% of African countries. The rapid increase in population pressure is also threatening the current SOC stock, leading to significant LUCC in Africa [35]. Research on land use practices with high potential for reducing soil carbon sources is limited. Wetlands have been identified as having the highest potential for carbon reduction, yet they are significantly understudied compared to farmland in meta-analyses. Similarly, studies on forest land comprise only half of those on farmland, despite forest soils containing over 40% of all organic carbon in the global terrestrial ecosystem.

2.2. Carbon Source Effect

Various sources of carbon emissions include the production and burning of fossil fuels, respiration, humic acid fermentation, organic matter decay, volcanic eruptions, and forest fires. Mohan Kumar and Aravindakshan identified key carbon contributors in the agriculture, forestry, and other land use sectors in India, such as enteric fermentation, fertilizer and manure management, rice paddies, crop residue burning, forest fires, shifting cultivation, and food waste, accounting for 25% of global anthropogenic carbon emissions [36]. Sun et al. reviewed 2439 articles from 2002 to 2021 on urbanization and carbon release, highlighting stages of urbanization and carbon release progression: budding, development, and maturity, with an increasing focus on balancing carbon emissions and urban development [37]. Yang et al. investigated carbon emissions from LUCC in the Yangtze River Economic Belt, noting a nearly fourfold increase in emissions from 1990 to 2008 [38]. Notably, cities with significant carbon sources are concentrated in economically developed downstream areas or mid-upstream urban agglomerations. The carbon source effect of land use and LUCC has garnered considerable attention and research, with studies ranging from basin to global scales. However, research on the mechanisms of land use or LUCC carbon source effects often lacks comprehensive summaries and is limited to specific land use types or regions.

3. Carbon Effects and LUCC

The modification of carbon sinks within terrestrial ecosystems plays a vital role in regulating and mitigating the greenhouse effect, considering the importance of terrestrial ecosystems on our planet. These carbon sinks include organic carbon in aboveground and belowground biomass, soil organic carbon (SOC), and organic carbon in litter within the ecosystem. Previous research has explored different scales and types of carbon sinks to analyze LUCC impacts from various viewpoints.

Different land use/cover types directly influence the carbon sink of terrestrial ecosystems, with varying capacities for carbon sequestration across different land use types. LUCC induces modifications in the carbon sink by altering existing land cover patterns, ecosystem structures, processes, and Earth functions, thereby impacting the physical cycle and energy flow of ecosystems extensively and with varying degrees of intensity. This transformation often results in significant carbon exchange, leading to increased greenhouse gas emissions [39]. LUCC stands out as a primary anthropogenic driver of the carbon cycle in terrestrial ecosystems [40,41], with studies indicating that LUCC ranks second only to fossil fuel combustion in contributing to the notable increase in atmospheric CO₂ concentrations [42]. Researchers have identified that the influence of LUCC on terrestrial ecosystem carbon sinks primarily stems from transformations in land use/cover types and alterations in land management practices.

3.1. Methods for Exploring LUCC Carbon Effects

Currently, researchers have investigated the influence of LUCC on carbon sequestration. For instance, Anindita et al. [43] examined the impact of LUCC on soil carbon sequestration in Indonesia, while Michel et al. [44] focused on the changes in carbon sinks due to LUCC in tropical forests in Africa. Their findings suggest that optimizing land use practices can help mitigate the decline in carbon sequestration rates. Common methods for estimating carbon sinks include field surveys and model simulations [45]. The traditional field survey approach involves collecting soil samples for physical and chemical analyses within the research area, which can be labor-intensive and time-consuming, making it less suitable for large-scale environmental studies. Since the 1990s, researchers have increasingly utilized remote sensing techniques in conjunction with modeling approaches to investigate carbon sequestration dynamics [46].

3.1.1. Land Use Simulation Method

The patch-generating land use simulation (PLUS) model combines the rule-mining approach for analyzing land expansion with the Cellular Automata (CA) model featuring a multi-type random seed mechanism. This model is utilized for investigating the factors influencing land expansion and forecasting the evolution of land use at the patch level. Wang et al. conducted a simulation of LUCC in Xinjiang, projecting that by 2050, carbon storage would be maximized under the SSP126 scenario, followed by the SSP245 and SSP585 scenarios [9]. Liang et al. examined the determinants of land expansion and the dynamic trends in Wuhan, predicting various land use configurations based on different optimization scenarios, thereby offering an enhanced decision-making tool for policymakers [47].

3.1.2. Carbon Sink Calculation and Simulation Methods

The Integrated Valuation of Ecosystem Services and Trade-Offs (InVEST) Model

The InVEST model is utilized for assessing ecosystem services, particularly in the calculation of carbon sinks, due to its reduced data requirements and simplified data acquisition process. This model is commonly employed for carbon sink calculations, enabling the evaluation of carbon sinks and its associated value within a specific spatial–temporal context on land. By using land use type as the assessment unit and incorporating regional land use/cover data along with carbon density information for each carbon pool, the model can determine ecosystem carbon sinks across various land use categories through grid-based calculations, thereby providing insights into the spatial distribution of regional carbon sink.

Recent scholarly research has focused on investigating the relationship between LUCC and regional carbon sink dynamics using the InVEST model. Scholars have conducted dynamic studies examining changes in regional carbon sinks over time and space. For instance, Yang et al. utilized the PLUS model to predict land use patterns under different scenarios for 2030, subsequently using the InVEST model to estimate future changes in carbon sinks under these scenarios, thereby exploring potential shifts in carbon sink levels and their future trajectories [48]. Similarly, Shao et al. applied the InVEST model to analyze variations in carbon sinks in Beijing from 1990 to 2018, followed by the use of the FLUS model to assess LUCC under three distinct urban development scenarios [49]. Furthermore, Lin et al. leveraged the InVEST model’s Carbon module to map the spatial-temporal distribution of carbon sink in Guangdong Province from 1990 to 2020, and then utilized the PLUS model in conjunction with 14 land use driving factors to predict land use patterns and associated carbon sink distribution for 2050 [30].

The Carnegie–Ames–Stanford Approach (CASA) Model

The CASA model primarily utilizes remote sensing technology to collect data on solar radiation, surface temperature, and precipitation necessary for the model. By integrating this information with land use and vegetation type distribution maps, the model examines the regional carbon sink and its distribution patterns based on the vegetation’s effective radiation absorption of light energy. The model is characterized by its user-friendly interface and practicality, as a significant portion of the essential data and model parameters can be acquired through remote sensing technology. The data obtained through this method offer extensive observations, long-term coverage, and high resolution. Consequently, the model has been extensively applied in assessing the carbon sinks and net productivity of terrestrial ecosystems at a regional scale.

GLObal Production Efficiency (GLO-PEM) Model

According to the CASA model, the GLO-PEM model incorporates vegetation respiration and assesses NPP by considering effective radiation absorption and utilization. This model relies on data obtained through remote sensing techniques, such as the plant coverage index (NDVI) and various meteorological parameters. Jiang et al. utilized remote sensing data and the GLO-PEM model to predict the net primary productivity of vegetation in the Huang-Huai-Hai Plain region and determined the carbon density of vegetation across different land use categories [50].

Carbon Exchange between Vegetation, Soil, and Atmosphere (CEVSA) Model

Currently, an increasing number of researchers are focusing on understanding the influence of LUCC on carbon sinks and predicting carbon sink changes in specific scenarios. Some scholars have integrated system dynamics and the CLUE-S model to simulate LUCC and the spatial distributions of different land types under specific conditions. They then assessed the impact of LUCC on carbon sinks by analyzing carbon density in various scenarios.

The Carbon Exchange between Vegetation, Soil, and the Atmosphere (CEVSA) model is a widely utilized dynamic analysis tool that comprises several sub-modules, including biophysical, plant growth, carbon distribution in plant organs, litter production, and biochemical sub-models.

In a study by Cao et al. focusing on Africa, it was noted that despite Africa contributing 1/5 of global NPP, the region experiences significant climate change [51]. The CEVSA model was employed to simulate the dynamic carbon cycle processes and changes in carbon sinks due to climate variations from 1901 to 1995. Some researchers have enhanced the CEVSA model by incorporating factors such as canopy interception and snowmelt effects on soil moisture, and have reduced the simulation time from “ten days” to “a day”. This improved model was utilized to analyze the spatiotemporal variations in terrestrial ecological carbon sinks following afforestation in the subtropical red soil hilly region.

The Intergovernmental Panel on Climate Change (IPCC) Greenhouse Gas Inventory Method

Using the IPCC greenhouse gas inventory approach to analyze alterations in carbon sequestration represents an empirical statistical technique. This method entails assessing the mean soil carbon density and the factors impacting the carbon pool during LUCC. A notable advantage of this statistical approach lies in its minimal parameter requirements, simplicity, ease of acquisition, and applicability in scenarios with limited or elusive data availability. However, it is not without limitations, such as oversimplifying the ecosystem carbon cycle process and failing to capture the influence of land use types on carbon sequestration within the model.

The Bookkeeping Model

The bookkeeping model is employed for determining the yearly net carbon alteration of land as a result of LUCC within a specific region. This model is a statistical estimation tool that encompasses a broad spectrum of carbon components per unit area, such as the carbon content present in organisms, soil, plant residues (e.g., litter), wood products, and LUCC. Various activities contribute to alterations in carbon stocks across different facets of the associated curve. The inaccuracies in the bookkeeping model primarily stem from discrepancies in LUCC data and carbon density information per unit area.

The Dynamic Land Ecosystem (DLEM) Model

DLEM was created to examine and forecast the behaviors and mechanisms of land-based ecosystems and coastal regions in the face of intricate global transformations arising from the interplay among climate, ecosystems, and human activities. In a recent study by Yu et al. [16], DLEM was employed to assess China’s carbon sequestration capacity, unveiling a substantial carbon sink within the country from 1980 to 2019. Notably, the proliferation of forests during this timeframe accounted for 44% of China’s overall carbon sinks.

As illustrated in

Table 1. Methods for assessing LUCC carbon effects.

Methods	Author	Results	Advantages	Disadvantages
PLUS model	[52]	Future land use pattern	It simplifies the analysis of land use change while maintaining a higher degree of precision in support of multiple types and complexities of land use change.	Land use demand is needed to run a simulation.
InVEST model	[31,38,49]	Carbon sink	Simple, convenient, and has a visual expression of evaluation results	Parameters need to be adjusted according to the study area; lack of space–time scale; accuracy and precision need improvement
CASA	[53]	Carbon sink	Mechanism model, suitable for large-scale research, widely used, fewer parameters	Non-North American areas need to adjust the parameters; the difference in vegetation is not considered; and there are high requirements for soil data.
GLO-PEM	[54]	Carbon sink	Fully driven by a remote sensing model, convenient	Accuracy and precision need improvement.
CEVSA	[55]	Carbon sink	Well applied at regional to global scales to model spatial–temporal variations in the carbon cycle of terrestrial ecosystems and their responses to climate change	Quantitative expression methods need to be adjusted for different scenarios.
IPCC	[56]	Carbon footprint	Data are easy to obtain; the model is complete and widely used	General, lack of pertinence
Bookkeeping	[57,58]	Carbon budget	Easy, convenient, data are easy to obtain	Uncertainties in the space dimension, limited by the accuracy of the data
DLEM	[17]	Carbon sink	Driven by multiple factors, fully-coupled cycles, concurrent simulation of major greenhouse gases, dynamic tracking	It depends on the accuracy and richness of the data.

PLUS model: the Patch-generating Land Use Simulation model. InVEST model: the Integrated Valuation of Ecosystem Services and Trade-Offs model. CASA: the Carnegie–Ames–Stanford Approach model. GLO-PEM: the GLObal Production Efficiency model. CEVSA: Carbon Exchange between Vegetation, Soil, and Atmosphere model. IPCC: the Intergovernmental Panel on Climate Change (IPCC) greenhouse gas inventory method. DLEM: the Dynamic Land Ecosystem (DLEM) model.

, the various research methodologies exhibit distinct research objectives, with each methodology presenting its own set of advantages and disadvantages. The distinctions among various models primarily pertain to differing requirements for data quality and variations in the accuracy of research outcomes.

3.2. Carbon Effects Change of Different Land Use Types Transformation

Each land use type is associated with specific sources of carbon emissions and carbon sequestration. The first column of

Table 2. Carbon sink and carbon source of different land use types (“+” represents carbon sink effect. “–“ represents carbon source effect).

Land Use/Cover Carbon Effects			Reference
Forest Land	Biomass +	Product −	[59]
		Leftover +	[60]
	Soil +		[61]
Waters	Biomass +		[62]
	Construction −		[63]
Grass Land	Biomass +		[64]
	Soil +		[64]
Cultivated Land	Biomass +	Product −	[65]
		Fertilization −	[66]
	Soil +		[67]
Unused Land	Biomass +		[68]
	Soil +		[68]
Construction Land	Energy Consumption −		[69]

displays six categories of land use. The symbols “+” and “−“ denote the carbon sequestration and carbon emission effects, respectively, as compiled from relevant studies. The carbon sinks associated with various land use types primarily result from soil carbon sequestration or biological carbon sequestration. Conversely, the primary carbon source is attributed to carbon emissions generated by human activities. The annotations in the table primarily encompass the global effects of various land use types, considering variations in climate, soil conditions, land management practices, and other regional factors. The conversion between different land use types is a complex process which has been categorized into six main research areas.

Forest land carbon encompasses both biomass carbon and soil carbon. Biomass carbon includes forest product carbon and residual carbon, such as aboveground carbon and slash. Forest ecosystems often utilize wood and other products for biomass energy consumption. According to Favero et al. [59], the carbon impacts of forest products exhibit temporal and spatial characteristics. While forest land contributes to carbon sequestration during plant growth, the production, transportation, and utilization of products can result in carbon emissions. Aboveground carbon represents the carbon content in living plants, encompassing all plant components (roots, understory forest, and forest floor). Slash refers to the carbon residue remaining on-site after timber harvesting [60]. Forest soil carbon is significantly influenced by factors like climate change, soil characteristics, and nitrogen deposition from the atmosphere [61]. Generally, a portion of the carbon sequestered by forest vegetation is transferred to the soil, establishing it as a carbon sink. While both plants and soils contribute to carbon storage in forest ecosystems, soil carbon storage becomes particularly crucial as the capacity of living tree biomass reaches its limits and faces heightened vulnerability to global disasters.

The primary sources of carbon impact in water bodies are attributed to the presence of plants, algae, and bacteria, as well as human-built water conservancy structures. These organisms engage in photosynthesis to capture carbon dioxide from the atmosphere and convert it into biomass energy. Conversely, the construction, operation, and maintenance of water conservancy facilities contribute to artificial carbon emissions.

Cultivated land carbon comprises biomass carbon and soil carbon. Despite the carbon storage within plants, a portion of this carbon is released during the decomposition of agricultural residues. Human utilization of organic fertilizers in farming practices also leads to significant carbon emissions. Changes in agricultural practices over the past five decades, such as the adoption of high-yield crop varieties, widespread use of mineral fertilizers, and reduced tillage, have resulted in increased net yields, productivity, and organic carbon content. Proper management of cultivated land has been shown to positively impact the global carbon budget.

In areas of unused land, plants play a crucial role in absorbing carbon from the atmosphere. Abbate et al. quantified the carbon sequestration effect of biomass based on factors such as biomass volume, age, diameter at breast height, and tree height [68]. The soil’s capacity to sequester carbon depends on the equilibrium between organic matter input into the soil and carbon loss due to natural processes like conversion and erosion.

Construction land primarily supports secondary and tertiary industries, as indicated by Li et al. [69]. Energy is consumed in the production, transportation, consumption, and waste management of products. The carbon sequestration effect of the limited vegetation on construction land is generally overshadowed by the carbon emissions resulting from substantial artificial energy consumption during production and daily activities.

3.2.1. Forest Land Transformation Carbon Effects

Numerous research studies have focused on forest carbon sinks across various forest ecosystems, such as tropical rainforests, mid-latitude forests, and coastal forests, due to their extensive forest coverage and significant carbon sequestration capabilities. Variations in climate, altitude, species composition, and soil conditions contribute to differences in the carbon sequestration capacity of forest lands.

The impacts of global warming include the carbon dioxide fertilization effect, which is expected to enhance the carbon sequestration capacity of forests. However, this effect may be counteracted by the reduction in forest area due to land use changes, resulting in an overall decrease in the total carbon sequestration capacity of forests.

Since the 1980s, researchers have been investigating the effects of global warming on terrestrial ecosystems using free-air CO₂ enrichment devices. Recently, scholars have started using detection attribution models to analyze the spatiotemporal variations in CO₂ fertilization effects [70]. Studies over the years have demonstrated that the rise in carbon dioxide concentration due to the greenhouse effect can boost the photosynthesis rate of vegetation, leading to an increase in the carbon sequestration capacity of forests [71].

Houghton observed that deforestation and the conversion of forests to other land-use types lead to elevated CO₂ emissions [72]. The extent of carbon emissions resulting from forest transformation varies depending on factors like climate, soil microorganisms, vegetation types, and human activities. Nevertheless, multiple studies have identified forests as the primary carbon sink, emphasizing that converting forests to alternative land use types diminishes their carbon sink capacity.

The conversion of forest land stands out as a significant factor contributing to the decline in carbon sinks. Between 1983 and 1990, the conversion of forest land to farmland and grassland represented 45% of the total LUCC area globally, yet it accounted for approximately two-thirds to three-quarters of the total carbon sink change attributed to LUCC. This underscores the substantial carbon sequestration potential of forest lands compared to other land use categories. Consequently, alterations in forest land uses can significantly impact terrestrial ecosystem carbon sinks. Notably, North America and Europe experience more pronounced carbon losses due to extensive farmland expansion encroaching upon woodland areas [73].

Tian and colleagues introduced a framework comprising the PLUS model and InVEST model to assess the spatiotemporal dynamics of LUCC and ecosystem carbon storage in Guangdong [53]. Through simulations conducted under three scenarios, they recommended a strategy of balancing urban expansion with environmental conservation by regulating population and economic growth to enhance the carbon sequestration capacity of forest lands. In a separate study, Yin et al. investigated the changing patterns and influencing factors affecting the efficiency of forest carbon sequestration at the provincial level in China [74]. Their findings indicated that variables such as GDP per capita, urbanization level, and the extent of highway networks positively impact carbon sequestration, while total imports and exports harm carbon sequestration efficiency. The drivers of forest land change exhibit varying degrees of significance across different regions. Generally, unsustainable agricultural practices among rural populations contribute to an increased demand for farmland. Other factors such as deforestation for industrial purposes; expansion of cultivated land, grasslands, and urbanization; as well as inadequate land management practices also play a role in altering forest land. Particularly in the context of rapid socio-economic growth, accelerated urbanization, and population pressures, the need to meet food demands has led to further expansion of cultivated land and grasslands.

Currently, significant emphasis has been placed on the alterations in carbon sinks resulting from shifts in forest land area. As shown in

Table 3. Summary of current research regarding the conversion carbon effects of forest land.

Conversion	Area	Carbon Effects	References
From primary forests to cultivation	The foothills of the Eastern Himalayan Region of India (Manipur)	Total soil C stocks decrease	[75]
Deforestation and reforestation	The Northeast China Forestry	Forest carbon sinks experience a trend of sharp decline to slow increase	[37]
Forest expansion	China	Contributes to nearly 44% of the national terrestrial carbon sink	[17]
Different intensities of human utilization	The Mayombe tropical forest	Carbon storage drops in both high- and moderate-utilization regimes	[44]
LUCC	China	N deposition causes net primary production and net ecosystem production to rise	[76]
Reforestation following harvesting; recent or historic disturbances	USA	C sequestration in forest biomass and soils is enhanced	[50]
Functional traits of trees and forest standing biomass change	Global	Soil organic carbon storage depends on climatic and soil conditions	[61]

LUCC: land use and land cover change.

, existing research primarily analyzes the changes in carbon sinks resulting from forest expansion or degradation due to human activities in specific regions. However, there is a relative dearth of research on comprehending the variations in forestry carbon sinks stemming from forestry management practices and calamities. Future studies could incorporate factors such as climate change, patterns in the forestry industry, occurrences of natural disasters, and modifications in land use categories into the analysis of land cover changes affecting forestry carbon sinks.

3.2.2. Water Transformation Carbon Effects

In terrestrial ecosystems, bodies of water such as rivers, glaciers, lakes, and wetlands represent a significant carbon reservoir, second only to forests. Carbon emissions primarily originate from water management infrastructure surrounding these bodies of water, while the organisms within them serve as substantial carbon sinks. Research on water bodies typically focuses on specific watersheds, river–lake ecological zones, or glaciers, with limited exploration of waters as distinct carbon sinks. Table 4 presents a summary of the various types of water-related land use cover changes and their corresponding carbon effects.

Zhang et al. conducted a study in the Yellow River Delta to examine the spatial–temporal patterns of carbon emissions, highlighting waters as the primary carbon sink in this region [77]. Han et al. investigated carbon dynamics in China’s Yangtze River from 1978 to 2010, noting a significant increase in carbon emissions due to LUCC, particularly the conversion of forests and waters to construction land [78]. Tang et al. assessed carbon sink variations resulting from LUCC in the Mekong River Basin between 2001 and 2019, identifying factors other than water–land use transitions as the main contributors to carbon release [10].

Jia et al. observed high carbon dioxide exchange fluxes in the western and southern regions of lakes on the Qinghai-Tibet Plateau (QTP), with lower fluxes in the eastern and northern areas [79]. These lakes function as carbon sinks, especially when accounting for annual ice cover periods in carbon budget estimations, showing an increasing trend in carbon sink capacity. However, uncertainties in estimating carbon exchange fluxes may lead to significant underestimation of the carbon sink potential of QTP lakes. Li et al. analyzed CO₂ fluxes in Qinghai Lake, the largest salt lake on the QTP, from 2013 to 2017, revealing higher CO₂ absorption during glacial periods compared to ice-free periods [80]. The cumulative CO₂ uptake by all salt lakes on the QTP amounts to approximately one-third of the net carbon sink of terrestrial ecosystems in the region. The study also suggested that as QTP salt lakes warm in the future, they may transition from carbon sinks to carbon sources due to reduced CO₂ absorption. Variability and uncertainties in traditional sampling methods and gas transport models used to estimate lake CO₂ fluxes can lead to divergent outcomes within the same geographical area.

Table 4. Summary of current research regarding the conversion carbon effects of waters.

Conversion	Area	Carbon Effects	References
Waters-related LUCC	The Yellow River Delta	Water is an important carbon sink	[77]
Waters to construction land	The Yangtze River	A climb in carbon emissions	[78]
Waters-related LUCC	The Mekong River Basin	Conversion of water is not the main cause of carbon release	[10]
Waters-related LUCC	Six North Africa coastal wetlands	Conversion of wetlands to others mainly decreases carbon sinks	[81]
Loss of wetlands	487 sites	C concentration and storage decrease	[82]
Loss of glaciers	Global	Loss of glaciers causes carbon release	[83]

LUCC: land Use and land cover change.

Table 4. Summary of current research regarding the conversion carbon effects of waters.

Conversion	Area	Carbon Effects	References
Waters-related LUCC	The Yellow River Delta	Water is an important carbon sink	[77]
Waters to construction land	The Yangtze River	A climb in carbon emissions	[78]
Waters-related LUCC	The Mekong River Basin	Conversion of water is not the main cause of carbon release	[10]
Waters-related LUCC	Six North Africa coastal wetlands	Conversion of wetlands to others mainly decreases carbon sinks	[81]
Loss of wetlands	487 sites	C concentration and storage decrease	[82]
Loss of glaciers	Global	Loss of glaciers causes carbon release	[83]

LUCC: land Use and land cover change.

Aitali et al. conducted a study on the impact of LUCC on carbon storage in six coastal wetlands in North Africa [81]. Their analysis revealed that the expansion of urban areas and the conversion of wetlands to other land use types resulted in a decrease in carbon storage in four of the wetlands. In a separate study, Tan et al. conducted a meta-analysis using a database of 487 sites to examine the effects of LUCC on soil carbon concentrations and reserves in coastal wetlands, peatlands, and riparian wetlands [82]. Their findings indicated that the average soil carbon concentration and storage decreased by 17.8 ± 10.3% and 23.2 ± 6.3%, respectively, following the conversion of these wetlands to various LUCC types. This suggests that LUCC plays a significant role in causing soil carbon loss in natural wetlands, thereby contributing to the greenhouse effect.

Hood et al. highlighted the importance of mountain and polar glaciers in storing organic carbon and projected that the accelerated loss of glacier mass could result in the release of 15 Tg of organic carbon [83]. The interconnection between terrestrial and aquatic carbon fluxes underscores the increasing significance of glaciers in the transfer of organic carbon from land to oceans.

While researchers have examined the carbon storage capacities of glaciers, lakes, and various types of wetlands, the diverse carbon sequestration capabilities of different water bodies and their varying performances across regions have led to a lack of unified research on water bodies’ carbon sink capacities. As summarized in Table 4, researchers often analyze changes in water body areas as part of their studies on global land use change. However, only a limited number of scholars focus on the degradation of wetlands or glaciers. Despite the robust carbon sink potential of water bodies, there remains a scarcity of studies addressing this aspect. Given the substantial variations among various water bodies, researchers encounter challenges when attempting to make horizontal comparisons. Recently, researchers have increasingly acknowledged various types of water carbon sinks, including ocean carbon sinks. Nevertheless, investigations in certain specialized domains, such as fishery carbon sinks, remain relatively limited. A comprehensive analysis of carbon sinks in all water body types will enhance awareness of the significance of water carbon sinks.

3.2.3. Grassland Transformation Carbon Effects

In recent years, there has been an increased focus among both domestic and international ecologists and soil scientists on the study of forest carbon sequestration. Vegetation in grasslands plays a crucial role in the absorption and release of carbon dioxide. During the initial stages of converting grasslands into forests, human disturbances to the soil can lead to reductions in the carbon sequestration capacity of grasslands. However, as surface vegetation and litter increase, the carbon sink of the area gradually improves over time, eventually reaching levels comparable to forests. Conversely, the conversion of grasslands to farmland may result in minimal changes to aboveground biomass, but can weaken the overall carbon sequestration capacity due to human activities.

While there has been extensive research on various aspects of forest carbon sinks, including different regions, periods, and types, as well as the impact of LUCC on forest carbon sinks, the study of carbon sinks in grassland ecosystems remains relatively limited and warrants further attention. The transition from grasslands to forested lands has been observed to significantly increase carbon sequestration. Studies by Kang et al. have shown that the rate of SOC storage loss was 11.29% in the first five years following afforestation, with a subsequent decrease in the rate of SOC loss in the 6 to 8 years post-afforestation, particularly in the 40 to 100 cm soil layer. Additionally, the average SOC storage was found to decrease by 3.5 kg/m3 following the conversion of grasslands to cultivated land [84].

Research evaluating the sensitivity of soil carbon to temperature has indicated that amidst global warming trends, policies promoting the conversion of farmland back to forest and grassland can enhance carbon fixation by plants in the soil. Wang et al. conducted a review of grassland changes in the QTP since the 1980s, suggesting that minimizing or ceasing grazing activities could aid in the restoration of degraded grasslands through adaptive management strategies [85]. Conversely, Chang et al. found that an increase in livestock numbers could shift grasslands from being carbon sinks to being carbon sources [86]. With the backdrop of climate change, grassland productivity has shown an increase, emphasizing the importance of sustainable management practices to preserve and enhance grassland carbon sinks while mitigating carbon emissions from these ecosystems.

As summarized in

Table 5. Summary of current research regarding the conversion carbon effects of grassland.

Conversion	Area	Carbon Effects	References
Grassland-related LUCC	The Dongting Lake	Forestation causes SOC to decrease in the first five years. Conversion from grassland to cultivated land leads to SOC loss.	[84]
Grassland-related LUCC	China	Conversion from grassland to cultivated land causes carbon release	[32]
Grassland-related LUCC	Qinghai-Tibetan Plateau grassland	Restoration of grassland leads to more carbon storage	[85]
Grassland-related LUCC	Global	The increase in livestock number contributes to the change in grassland from a carbon sink to a carbon source.	[86]

LUCC: land use and land cover change.

, scholars have primarily concentrated on the changes in grassland area during the global land use change process. However, there is a notable lack of research specifically analyzing and studying the carbon effects of grassland ecosystems. The alteration of grassland ecosystems frequently encompasses a range of other land use categories, prompting a systematic examination of grassland transformation at the regional or global levels. Predominantly, conversions involving grassland entail transitions to cultivated land, with a prevailing consensus indicating a decline in carbon sequestration capacity following such conversions. Despite this, limited scholarly attention has been devoted to investigating this aspect within the realm of grassland management. Furthermore, given the prevalence of grasslands, communities frequently depend on animal husbandry as their primary means of production. When examining grassland carbon sinks, it is essential to factor in the carbon emissions associated with animal husbandry as a strategy for land development and utilization.

3.2.4. Cultivated Land Transformation Carbon Effects

The transformation of agricultural land also plays a significant role in affecting the carbon sequestration capacity of terrestrial ecosystems. Human activities primarily contribute to carbon emissions from cultivated land, with the specific emissions being contingent upon agricultural practices. Numerous research studies have indicated that transitioning farmland to forests and grasslands can enhance the storage of organic carbon. Table 6 presents a summary of various types of cultivated land use cover changes and their corresponding carbon effects.

Jiang et al. observed that the conversion of cultivated land in the Huanghuai Plain region influenced the carbon sequestration capacity of vegetation [87]. Their findings suggested that during the period from 1988 to 2000, the conversion of cultivated land resulted in a 0.24% reduction in vegetation carbon sequestration within the study area. Notably, the most significant factor contributing to this decline was the conversion of cultivated land to urban or construction areas.

Numerous scholars have conducted extensive research on the effects of the policy of converting farmland back to forest and grassland on soil and vegetation carbon sequestration. Their studies have predominantly utilized spatial analysis rather than temporal analysis to examine variations in carbon sequestration across different stages of succession, soil depths, and vegetation types [7]. The Loess hilly region of China, characterized by ecological degradation and severe soil erosion, has been a focal point for investigating carbon sequestration capacity. For instance, Liu et al. assessed the carbon sequestration potential following the implementation of conversion of farmland to forests in this region [88]. Their findings indicated that over time, vegetation carbon sequestration increased annually, while soil carbon sequestration initially decreased before rising, aligning with similar conclusions drawn by Goulden et al. [89]. Shen and Zhang conducted a study on Robinia pseudo acacia plantations in the Loess hilly region post-farmland conversion using field sampling and other methodologies. They observed that soil carbon sequestration was notably influenced by slope orientation and the duration of time since farmland conversion [90].

The preservation of cultivated land has garnered significant attention in recent years. Initially, due to urban expansion, cultivated land was predominantly converted into construction sites, resulting in a substantial loss of carbon sinks and an increase in carbon emissions. However, as public awareness has grown, efforts to convert cultivated land back to forested areas have been increasingly implemented, generally leading to enhanced carbon sequestration.

The carbon sequestration role of arable land remains a controversial topic due to human agricultural activities, particularly the use of agricultural machinery and application of fertilizers and films. As summarized in Table 6, scholars have reached a consensus that converting farmland back to forests will enhance carbon sinks. However, it is important to note that the extent of the increase in carbon sinks may vary over time. Future researchers are encouraged to investigate human agricultural activities and the biological processes of farmland comprehensively to enhance the understanding of the intensity of carbon storage capacity in farmland.

Table 6. Summary of current research about the conversion carbon effects of cultivated land.

Conversion	Area	Carbon Effects	References
Cultivated land-related LUCC	The Huang-Huai-Hai plain	Conversion of cultivated land to construction land led to a decrease in carbon sinks	[87]
From cultivated land to forest land	The Tibet Autonomous Region	Carbon sinks rose	[7]
From cultivated land to forest land	The Loess hilly region	The vegetation carbon sink increased year by year, while the soil carbon sink decreased first and then increased	[88]
From cultivated land to forest land	The Loess hilly region	The soil carbon sink was significantly affected by slope aspects and years of returning cultivated land	[90]

LUCC: land use and land cover change.

Table 6. Summary of current research about the conversion carbon effects of cultivated land.

Conversion	Area	Carbon Effects	References
Cultivated land-related LUCC	The Huang-Huai-Hai plain	Conversion of cultivated land to construction land led to a decrease in carbon sinks	[87]
From cultivated land to forest land	The Tibet Autonomous Region	Carbon sinks rose	[7]
From cultivated land to forest land	The Loess hilly region	The vegetation carbon sink increased year by year, while the soil carbon sink decreased first and then increased	[88]
From cultivated land to forest land	The Loess hilly region	The soil carbon sink was significantly affected by slope aspects and years of returning cultivated land	[90]

LUCC: land use and land cover change.

3.2.5. Unused Land Transformation Carbon Effects

The vegetation coverage on unused land is minimal, resulting in weak soil functionality and a limited soil carbon sequestration capacity. Due to the relatively small carbon sink and source potential of unused land, investigations into this type of land are typically only considered within the context of broader regional systematic research efforts.

Yang and Liu conducted a study in the Chang-Zhu-Tan urban agglomeration from 1995 to 2018, focusing on carbon emissions resulting from LUCC [48]. Their findings indicated that the carbon impacts stemming from the conversion of unused land were negligible. Li et al. examined LUCC dynamics and carbon storage in Fujian Province both before and after the implementation of the Ecological Conservation Pilot Zone Program (ECPZP) [91]. Their research revealed that the ECPZP contributed to the preservation of ecological spaces and GDP stability, and the unused land area exhibited stability with no substantial fluctuations in carbon storage [91].

Despite the importance of understanding the carbon implications of unused land conversion, research is scarce in this area. Given the limited carbon sequestration potential of unused land, treating it as a standalone research subject holds minimal practical significance when investigating changes in carbon sources and sinks resulting from LUCC.

3.2.6. Construction Land Transformation Carbon Effects

The carbon emissions associated with the conversion of land for construction primarily stem from the fossil fuel energy utilized in human production and daily activities. Alterations in land use can lead to significant fluctuations in carbon emissions. The rapid urbanization process has resulted in the conversion of various land types into construction sites, leading to a notable rise in carbon emissions due to limited greening efforts in these areas [92].

As urbanization and industrialization accelerate, the trend of construction land encroaching on agricultural land becomes increasingly apparent. While deforestation rates have been declining since 1990, urban expansion has surged over the past three decades. The conversion of agricultural land to construction sites results in a reduction in vegetation, thereby diminishing the ecosystem’s carbon stock. Furthermore, construction land exhibits the highest total carbon emissions and intensity among different land types, surpassing others by several dozen or even hundreds of times.

The investigation of urban soil carbon pools and their dynamics has gained attention in the context of global climate change. However, research on urban soil carbon pools lags behind studies on other terrestrial ecosystems. Considering the carbon density and the high likelihood of forest conversion to construction land in tropical regions, the Americas and Africa are projected to experience the most substantial total carbon loss by 2030, estimated at 0.5 and 0.49 Pg C, respectively. Studies by Seto et al. indicate that development projects in Baltimore County, USA, could disrupt 27 t C per 2600 m² of construction activities [93]. In China, Tao et al. found that the urban core of Changzhou has a terrestrial carbon sink ranging from 0.11 to 0.32 Tg C, significantly lower than that of the urban fringe area, which ranges from 2.41 to 7.50 Tg C [94].

Initially, urbanization efforts led to a rapid expansion of construction land. However, as concerns over climate change grew, the pace of land transformation was moderated. Given that urbanization is crucial for societal progress, current research focuses on transitioning between different land use types, enhancing scientific and technological capabilities, and improving management practices to address the escalating carbon emissions resulting from the expansion of construction land.

3.3. Carbon Effects of Different Land Use Types Transformation

Figure 3 shows the general differences in carbon effects among six kinds of land use categories. Clockwise conversion results in a reduction in carbon sink capacity or an elevation in carbon sources, whereas counterclockwise conversion leads to an augmentation in carbon sink capacity. The following section provides a detailed explanation of the carbon effects resulting from the mutual transformation among the six land use types.

Constrained by natural conditions, the transition from forest land to water bodies is infrequent. Variations in biomass and soil resulting from this transformation are contingent upon diverse factors such as climate, soil composition, and plant life, rendering the overall trajectory uncertain. Typically, the conversion of forest land to water necessitates initial clearing and treatment of ground vegetation, causing a significant decline in the region’s carbon sequestration capacity. Carbon sequestration in water bodies is primarily facilitated by plankton, algae, benthic organisms, and aquatic plants. However, the newly formed water bodies may not provide a suitable habitat for these organisms, resulting in a diminished carbon sequestration capacity in the newly established aquatic environment. As the ecosystems of water bodies gradually stabilize over time through the proliferation of various organisms and microorganisms, the water bodies can eventually realize their full carbon sequestration potential. Nevertheless, the construction of water management infrastructure can lead to carbon emissions. Consequently, the conversion of forest land to water bodies inevitably results in carbon storage loss, although sustained maintenance may enable the water bodies to function as carbon sinks in the long term.

Conversely, the transition from water bodies to grasslands is also uncommon. While water bodies generally exhibit a higher biomass carbon sequestration capacity compared to grasslands, this capacity diminishes upon conversion. The comparison of soil carbon sequestration between the two ecosystems is challenging. Dismantling water management structures can mitigate carbon emissions. Following the disruption of the aquatic environment, the establishment of a grassland habitat is a time-consuming process. Newly formed grasslands exhibit a nascent carbon sequestration capacity due to the developmental stage of grassland vegetation. Although organic matter stored in the soil aids in the rapid growth of new grasslands, the transition from a water to a grassland environment is a gradual process. Given that woodland plants typically possess a greater capacity to absorb and sequester carbon compared to grassland vegetation, the conversion from woodland to grassland results in reduced carbon storage. Forest land generally harbors higher soil carbon storage levels than grasslands, leading to diminished carbon sequestration in both the short and long term upon conversion from woodland to grassland.

The transition from grassland to cultivated land has been extensively researched, with a focus on the impact on carbon storage. Generally, the conversion results in a decrease in the carbon sink capacity due to reduced soil carbon storage. The carbon effects of tillage contribute to a lower total biomass carbon sink in cultivated land compared to grassland. Farming activities on cultivated land involve significant organic fertilizer input and carbon emissions from the production and use of agricultural equipment. Intensive crop production on cultivated land also leads to the release of carbon into the atmosphere, particularly through straw burning in the initial stages. Consequently, any conversion of forest land, water bodies, or grassland to farmland driven by human activities results in an increase in carbon source effects and a decrease in carbon sink effects.

Despite the carbon fixation by plants on cultivated land, the carbon sink effect remains superior to that of unused land. Transitioning from cultivated land to unused land results in a substantial reduction in soil and biomass carbon sinks due to fewer plants absorbing CO₂. Typically, the emergence of unused land is attributed to factors such as slope, soil quality, water availability, and altitude, which limit human utilization of the land, thereby preventing land use changes to unused status.

Converting land from other types to construction land leads to significant carbon emissions from energy consumption, reducing soil and biomass carbon sinks. Although green belts may be established on construction land, their carbon sequestration impact is minimal compared to the emissions resulting from human energy consumption during production and daily activities. Urbanization is an inevitable aspect of social development, prompting the need for research on optimizing land use efficiency and transitions between different land types.

Conversely, transitions in the opposite direction result in an increasing carbon sink trend. In recent years, heightened awareness of the link between climate change and human activities has spurred initiatives such as converting farmland back to forests or grasslands, as well as wetland conservation. Expansion of forested areas and ecological restoration efforts have gradually enhanced the global carbon sink capacity.

3.4. Carbon Effects of Management Modes

Many analyses typically consider changes in carbon sequestration resulting from the conversion of various land use types. However, the impact of different management practices, particularly in cultivated land management such as planting patterns, irrigation, fertilizer application, tillage methods, crop density adjustments, and crop variety changes, is often overlooked in global LUCC model assessments.

In forest ecosystems, management practices like fire occurrences, wood harvesting, and rotation schemes play crucial roles. Despite their significance, only a limited number of global models account for management activities within forested areas, which can potentially lead to substantial reductions in forest carbon stocks. For instance, selective logging in the Amazon region has been shown to increase emissions by 15–19% solely from deforestation [95]. Houghton estimated that the combined net emissions from logging and rotation practices increased by 28% based solely on land cover changes [96]. Additionally, Shevliakova et al. estimated that harvest and conversion activities alone contributed to an additional release of 32–35% of the net global land cover change flux [97].

4. Carbon Effects and Human Well-Being

Human-induced carbon emissions have led to a rise in global temperatures, resulting in a notable escalation in the frequency and severity of natural calamities. The contemporary climate landscape is marked by a proliferation of extreme weather occurrences, including droughts, floods, hurricanes, heatwaves, wildfires, ice storms, and polar vortexes, all of which contribute to a decline in HW.

4.1. Existing Linkage between Carbon Effects and Human Well-Being

Scholars commonly investigate the connection between HW and carbon emissions by using energy consumption as a key factor [98]. Objective indicators such as Energy Intensity of Well-Being (EIWB), Carbon Intensity of Well-Being (CIWB), and the Human Development Index (HDI) are frequently employed in this research. Additionally, some researchers have conducted empirical studies involving the use of questionnaires to gather subjective data on HW. As illustrated in

Table 7. A summary of existing research on the relationship between carbon and HW.

Method	References	Site	Time Scale
Human Development Index (HDI)	[101]	Global	1975–2005
Carbon Intensity of Well-being (CIWB)	[102]	70 nations	1995–2013
	[103]	125 countries	1990–2017
	[69]	China	1995–2016
	[104]	153 nations	1961–2013
	[105]	9 lower-middle-income countries	2000–2018
	[106]	114 countries (or regions)	1980–2014
Energy Intensity of Human Well-being (EIWB)	[107]	12 Central and Eastern European (CEE) nations	1992–2010
	[101]	156 country samples	1975–2005
Happiness (questionnaire)	[108]	Australia	2010

, the subjective assessment of human well-being obtained through questionnaire survey methodologies demonstrates a high degree of accuracy. However, this approach frequently encounters challenges in data collection and is typically limited to analysis at a singular time point [99,100]. In contrast, studies utilizing statistical data such as HDI, CIWB, and EIWB are capable of conducting extensive and longitudinal research. Nonetheless, these studies often face skepticism regarding their credibility.

4.1.1. Human Development Index (HDI)

The utilization of the HDI encompasses more than just the increase in incomes, as it encompasses three key dimensions of HW: health and longevity, education attainment, and decent living standards. The HDI amalgamates indicators such as life expectancy at birth, education level, and per capita GDP to form a comprehensive measure [109]. Steinberger and Roberts conducted a study examining the interplay between the human development index, energy consumption, and carbon emissions. Their findings suggest that despite population growth, the global energy consumption and carbon emissions necessary to fulfil human needs are expected to gradually decrease [101].

Scholars have begun to view the HDI as a novel gauge of HW [45]. Ali et al. devised a method to calculate the HDI by incorporating factors such as gender inequality, environmental degradation, economic distress, and economic growth. Their analysis revealed that economic distress was the primary contributor to unhappiness, while gender inequality and economic growth also significantly impacted HW in Pakistan between 1980 and 2019.

4.1.2. Carbon Intensity of Human Well-Being (CIWB)

The concept of CIWB pertains to the ratio of carbon dioxide emissions per unit of life expectancy at birth. Research on CIWB involves quantitative analysis at a macro level to examine the correlation between different forms of socioeconomic development or well-being and carbon dioxide emissions. Initially proposed by Dietz, Rosa, and York, the majority of current studies on CIWB have been conducted by Jorgenson and his research team [107].

Scholars have approached CIWB research from various angles. For instance, Ergas et al. observed that the association between different aspects of gender equality and CIWB varies between developed and developing nations [102]. Wang et al. investigated the influence of urbanization on CIWB across 125 countries from 1990 to 2017, noting a decline in CIWB values over the study period [103]. Li et al. assessed CIWB panel data from 30 provinces in China spanning from 1995 to 2016, concluding that economic growth is likely to positively impact sustainable development. Nonetheless, environmental policies are deemed necessary to counteract unforeseen environmental harm [69]. Greiner and McGee delved into the asymmetric relationship between economic activity and CIWB in 153 countries from 1961 to 2013 [104]. Meanwhile, Hai et al. determined that economic development, encompassing GDP and annual FDI, had a notable adverse effect on CIWB [105]. This implies that economic growth led to a reduction in HW across the sample during the study period. However, this impact is deemed unstable, underscoring the importance of these countries making informed decisions regarding sustainable development strategies. Furthermore, the study highlighted a significant positive relationship between energy consumption and CIWB.

4.1.3. Energy Intensity of Human Well-Being (EIWB)

Jorgenson and colleagues conducted a study involving a sample of 12 Central and Eastern European (CEE) countries to examine the temporal relationship between EIWB and economic development spanning from 1992 to 2010. The findings of the study revealed the evolving connection over time between EIWB and development, highlighting potential avenues for enhancing sustainability in CEE countries [108]. In a related study, Steinberger and Roberts investigated eight relationships by analyzing four indicators of human development—namely, life expectancy, literacy, GDP per capita, and the Human Development Index—in conjunction with two aspects of resource utilization and environmental impact: primary energy consumption and carbon emissions [101].

4.1.4. Others

Ambrey and Daniels conducted a study that linked data from the Australian Household, Income, and Labor Dynamics Survey with household spending and carbon footprint derived from greenhouse gas emissions [109]. Their research revealed a negative correlation between higher carbon footprints and levels of happiness. Wang et al. analyzed panel data spanning 114 countries (regions) from 1980 to 2014 to establish a carbon intensity index for HW [106]. They explored the spatial evolution model and spatial agglomeration characteristics of this index using spatial autocorrelation techniques. Additionally, other scholars have investigated the relationship between satisfaction and various low-carbon practices such as heating and transportation in housing.

4.2. Low-Carbon Human Well-Being

To enhance HW, it is essential to address carbon emissions resulting from resource consumption. Embracing low-carbon practices may restrict access to materials and potentially diminish HW. Conventional methods for evaluating HW have not been able to effectively assess the balance between low-carbon initiatives and HW. As illustrated in Figure 4, human activities in different domains such as energy, socio-economic factors, and the ecological environment have an impact on human well-being. Conversely, human well-being also influences future human actions. The concept of low-carbon HW introduced in this study aims to quantify the impact of carbon emissions on HW, considering both carbon sources and carbon sinks.

Table 8. Indicators of low-carbon HW.

Carbon Effects	Indicators	Calculation Method	Units
Carbon source	Carbon emission intensity	CO2 emissions/GDP	Kg/$
	Energy consumption per capita (excluding electricity)	Energy equivalent to total standard carbon consumption/population (excluding electricity)	Kg/capita
	Per capita electricity consumption	Electricity consumption/population	kW·h/capita
	Share of clean energy consumption	Renewable energy consumption/total energy consumption	%
	Per capita livestock captive	Per capita livestock captive	Livestock/capita
Carbon sink	Per capita cultivated land area	Per capita cultivated land area	km2/capita
	Per capita forest land area	Per capita forest land area	km2/capita
	Per capita grassland area	Per capita grassland area	km2/capita
	Per capita water area	Per capita water area	km2/capita

HW: human well-being.

presents the low-carbon hardware evaluation index system that has been developed. By promoting the idea of low-carbon HW, more individuals can recognize the interconnectedness of low-carbon practices and HW, leading to increased engagement in such efforts. It is suggested that adopting low-carbon behaviors can enhance HW, while improved HW can in turn motivate individuals to further embrace low-carbon practices.

The carbon emission intensity serves as an indicator of the economic cost associated with CO₂ emissions necessary for economic progress [110]. A higher index value signifies lower efficiency. The evaluation of the energy consumption structure in the research area is conducted through two perspectives: energy consumption per capita(excluding electricity usage and electricity consumption) and the share of clean energy consumption. This assessment reveals that regional development sustainability is compromised when the proportion of clean energy is inadequate and total energy consumption is high, potentially leading to diminished HW. The per capita livestock holdings serve as a reflection of regional carbon emissions, particularly in areas where animal husbandry is a primary industry. A higher value in this context indicates increased per capita carbon emissions, resulting in heightened environmental burden and reduced HW. The per capita ownership of cultivated land, forest land, grassland, and water area reflect the ownership of the four primary carbon sinks per capita, providing insight into the region’s carbon sink capacity. A higher corresponding index value indicates a stronger carbon sink capacity, which in turn can enhance HW.

5. The Framework of the LUCC-CEs-HW System

The majority of scholars consider ecosystem services as a crucial link connecting LUCC with HW [24]. LUCC, being a significant outcome of human activities, directly influences the structure and functioning of ecosystems and their ability to provide ecosystem services. Ecosystem services are fundamental for maintaining natural environmental conditions necessary for human survival, and are established and sustained by ecosystems and biological processes. Changes in ecosystem services can impact various aspects of HW, either directly or indirectly [46]. Extensive research has been conducted globally on the effects of large- and medium-scale LUCC on ecosystem services and HW. While studies suggest that human-induced LUCC, such as industrial land expansion, can benefit HW, the impact of LUCC on HW varies and may have delayed effects that cannot be immediately addressed.

Different land use types exhibit varying carbon sources or carbon sink effects, and LUCC leads to alterations in land cover types, land use patterns, and intensity. The level of human intervention on different lands results in varying amounts and structures of energy use, leading to different carbon sources. LUCC also affects the carbon sink capacity of plants and soil. Changes in carbon sources and sinks indirectly influence various aspects of human life through the global ecological cycle.

A challenge arises from the absence of a universal measure of HW. Various studies have developed assessment indicators to evaluate human prosperity based on different understandings of HW, resulting in diverse research areas, groups, and scales. Some researchers have explored the impact of LUCC on HW by examining noise pollution and cluster effects resulting from LUCC as direct consequences. Currently, there is a lack of research on the combined effects of LUCC, carbon dynamics, and HW, which underscores the need for a comprehensive framework. Through the proposed framework, the interconnections among LUCC, ecosystem services, and HW can be quantitatively analyzed using system model simulations and scenario predictions in future studies.

It is widely acknowledged that maintaining a lifestyle of material abundance necessitates a substantial amount of energy consumption. In the long run, the excessive use of fossil fuels by individuals may indeed lead to a rapid enhancement of human welfare in the short term. However, the resultant global warming could render the Earth inhospitable for human habitation, ultimately jeopardizing human welfare. There is a growing interest in promoting the concept of low-carbon human welfare, which underscores the enhancement of human well-being through methods that have a relatively low carbon footprint. This entails prioritizing the enhancement of energy efficiency, promoting the adoption of clean energy sources, avoiding inefficient energy consumption practices, and integrating considerations for human welfare into the fabric of social development. As illustrated in Figure 5, we have developed a conceptual framework that elucidates the relationship among carbon effects, low-carbon human well-being, and changes in land use cover. This framework is further explained in the following sections.

(1)

LUCC involves alterations in land use types, management practices, land use intensity, and land use patterns, which can impact the carbon sink and carbon source within a specific area. For instance, transitioning from forest to construction land can lead to the destruction of plant life in the forest, diminishing its capacity to absorb carbon dioxide. This shift results in increased carbon emissions due to construction activities and heightened human presence, leading to greater energy consumption and subsequent carbon emissions. Such changes in LUCC, including other variations in land use types, have diverse operational principles, but collectively influence carbon effects. Modifications in land use intensity, such as intensive farming practices requiring more inputs like fertilizers and generating more waste, can also elevate carbon emissions compared to low-intensity land use. Various land management techniques, like implementing fire prevention measures in forests or altering cultivation methods in agricultural lands, can impact their carbon sink capabilities. Although the carbon effects of alterations in land use patterns are not definitively understood, their distribution can influence carbon effects across the area.

(2)

The carbon effects in a given area are determined by the balance between carbon sinks and carbon sources. Factors influencing carbon effects correspond to indicators of low-carbon HW, with the latter being heavily reliant on carbon sink and carbon source elements. Changes in carbon source effects, such as construction activities, energy consumption, deforestation, and combustion, can lead to shifts in related indicators of carbon sources in low-carbon HW. The effects of biomass and soil carbon sinks are manifested in indicators like per capita land area of cultivated land, forest land, grassland, and water bodies in low-carbon HW assessments.

(3)

Human well-being stands as a fundamental development objective in society, prompting adjustments in land use policies based on well-being status and objectives. Low carbon is a crucial aspect of HW and represents a future development trend. In instances where low-carbon HW is lacking, considerations are made regarding the constraints of well-being when planning LUCC. For example, in regions with limited per-capita land area of types conducive to carbon sinks, leading to low-carbon HW, strategies may involve increasing the proportion of land types with high carbon sink capacities, such as forest land.

(4)

The well-being of individuals in a low-carbon society is influenced by LUCC. Factors such as the amount of cultivated land, grassland, water bodies, and forest land per person are integral to low-carbon HW. Any increase in construction land area, degradation of forest and grassland, and decline in carbon sinks would harm low-carbon HW. Higher land use intensity leads to increased energy consumption and higher carbon emission intensity, consequently diminishing low-carbon HW. Implementing an optimized land use management model and pattern, including improved farming and grazing practices as well as energy consumption structure, can enhance low-carbon HW.

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The establishment of a low-carbon HW index is a fundamental objective of human society and is crucial for the sustainability of human civilization. To enhance low-carbon HW, society must develop policies that regulate carbon impacts, such as optimizing energy consumption structures, restricting the use of non-clean energy, and controlling carbon emissions from activities like farming, grazing, and construction.

6. Discussions and Implications

6.1. LUCC and Carbon Effects

Before the 1990s, there was considerable attention given to the impact of LUCC on the carbon sink of the terrestrial environment. Human-induced LUCC has been a primary driver of changes in carbon sinks within terrestrial ecosystems over recent centuries, emphasizing the crucial role of forested areas in regulating carbon sequestration. However, the variability in carbon sinks within terrestrial ecosystems is subject to high uncertainty due to the substantial influence of climate change. With the acceleration of global warming, the impact of environmental warming on the carbon sink of terrestrial ecosystems is increasing. Researchers have employed models such as CEVSA, GLO-PEM, and others to distinguish between the effects of climate change and LUCC on carbon sinks, leading to a refinement of research in this field around the early 21st century.

The carbon sinks of terrestrial ecosystems comprise soil carbon and vegetation carbon components. Studies have examined the response of soil carbon sequestration at different depths to LUCC, while the assessment of vegetation carbon sinks often relies on annual remote sensing data to project the characteristics of vegetation carbon sequestration over the long term [111,112]. The relevance of these models has been enhanced by advancements in science and technology, particularly in light of the significant greenhouse effect. Post-2010, an increasing number of researchers have focused on analyzing the spatial and temporal dynamics of the carbon impact of LUCC, as well as developing spatial patterns. Various regions are categorized based on their carbon budgets, and scenario simulations and other techniques are utilized to simulate spatial planning strategies under low-carbon-emission scenarios.

The conversion of forested land is a major contributor to the decline in carbon sinks, with LUCC exhibiting distinct spatial and temporal characteristics in its carbon effects. In the context of global warming, policies aimed at converting farmland back to forests and grasslands may ultimately enhance carbon sequestration. The transformation of agricultural land into urban or construction areas leads to a reduction in vegetation cover, thereby diminishing the carbon stock of ecosystems. However, the carbon emissions associated with construction land use are predominantly driven by other factors, including the total area and intensity of carbon emissions.

However, there are several existing issues in the current research, such as insufficient data and uncertainties, a lack of investigation into the carbon sequestration potential and quality of terrestrial ecosystems, and the necessity for relevant studies on optimal land use patterns in scenarios with low carbon emissions. Many researchers tend to overlook the role of land use intensity and management, instead concentrating on the changes in carbon sources and sinks resulting from LUCC alterations. Lai et al. highlighted that China’s rapid economic growth significantly influenced the substantial shifts in land use observed in recent decades [113]. Failures in land management, forest fires, and pests led to substantial carbon losses (approximately 101.8 Tg C/y). LUCC contributed about 1.45 Tg C/y of total fossil fuel emissions during 1990–2010. It is crucial to acknowledge the importance of effective land use management [114]. Furthermore, the majority of studies have disregarded the intensity of land use, with only a few scholars considering it when assessing the carbon impacts of LUCC, particularly in agricultural areas.

6.2. Carbon Effects and Human Well-Being

The size and extent of a study play a significant role in shaping the conclusions drawn by scholars. Extensive research has indicated that non-industrial nations exhibit strengths in energy usage and expectations for daily comforts, while developed nations face challenges in decoupling these factors [115]. A detailed analysis has characterized HW as being reliant on a range of essential household goods and services, establishing criteria based on demand and estimating the associated energy consumption and carbon emissions. Despite global research efforts, a consensus on the carbon impacts on HW remains elusive. Consequently, there is a need for a standardized evaluation framework that can be tailored to different countries and regions at varying stages of development [116]. The interplay between low-carbon initiatives and HW has not been thoroughly explored, with limited discussion on the potential trade-offs and synergies between the two. Balancing the imperative of low-carbon development with the enhancement of HW poses a challenge. To address this, the concept of low-carbon HW is proposed, emphasizing the need to foster new approaches that promote both low-carbon practices and human happiness and societal advancement simultaneously for the sustainable progression of human civilization.

The energy consumption structure can be altered by the incorporation of renewable energy sources like photovoltaics, wind power, hydropower, and nuclear power [117,118]. This alteration aims to diminish carbon emissions while safeguarding human well-being. Subsequent quantitative research in the field can involve configuring various carbon emissions and human welfare constraints through model simulations. This approach can help to identify an optimal solution that meets the dual objectives of maintaining a relatively high level of human welfare and promoting low-carbon development.

6.3. LUCC and Human Well-Being

Numerous scholars utilize ecosystem services (ES) as a framework to assess the effects of LUCC on HW [119]. While research on ES is well-established, the investigation into HW lacks standardization. Various studies have developed assessment criteria for gauging HW based on differing interpretations, leading to variations in research focus, authorship, and scope [120,121]. While some researchers have explored alternative perspectives, the examination of HW is often tied to specific areas of study, such as noise pollution and energy consumption.

In fact, as a crucial component of the social ecosystem, land transfer exerts an influence on human well-being that extends beyond direct effects like noise pollution and ecosystem service value [122]. Future research endeavors should encompass the holistic examination of the interplay between economy, ecology, and social development, thoroughly exploring their potential impacts.

6.4. “LUCC-CEs-HW” System

This paper presents a novel conceptual framework termed LUCC-C-HW, which integrates three distinct concepts into a cohesive system. The framework elucidates the interconnections between LUCC and C and LUCC and HW, as well as the relationship between carbon and HW. It provides a succinct overview of the intricate mutual influences among these elements.

7. Conclusions

Predominant previous research has independently focused on land use and land cover change (LUCC), carbon effects (CEs), and human well-being (HW), or on the interactions among these three aspects. Nevertheless, this conventional approach is deemed inadequate for adequately tackling the 17 Sustainable Development Goals (SDGs) and fulfilling international climate accords. Through a comprehensive review, this research proposes a holistic LUCC-CEs-HW framework to synthesize previous research outcomes and advance future works. The principal discoveries of this work are delineated as follows:

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Land Use and Land Cover Change Carbon Effects:

Existing research on the carbon implications of LUCC predominantly focuses on the reciprocal conversion between forests and other land use categories. These studies commonly use soil organic carbon as a measure of carbon implications and evaluate the effects of LUCC using satellite remote sensing data and associated model simulations. However, there is a noticeable gap in the consideration of land management practices such as agricultural techniques, irrigation, fertilization, deforestation, and natural disasters, which significantly impact the carbon implications of LUCC. While some researchers have explored low-carbon land use patterns, a consensus has not yet been reached, highlighting the need for further refinement.

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Human Well-being Carbon Effects:

Research on the correlation between carbon effects and HW at a macro level quantifies carbon effects using panel data and examines their relationship with HW. Previous works on different countries or regions with varying levels of development suggest a robust link between energy consumption and living standards, especially in developing nations. To comprehensively assess the impact of carbon emissions on HW, it is crucial to develop a standardized evaluation index system that can be applied across regions.

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Low-carbon Human Well-being:

Conventional approaches for evaluating HW lack the ability to consider the balance between low carbon emissions and HW. This research introduces the notion of low-carbon HW, which examines the variations in carbon-related HW arising from the carbon emissions and absorptions linked to HW activities.

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The LUCC-CEs-HW Framework:

LUCC induces alterations in carbon sinks and sources within a particular region. The carbon effects result from the combined influence of carbon sinks and sources, which are in line with the indicators of low-carbon HW. Achieving low-carbon HW is heavily dependent on factors related to the carbon effect and, to some extent, on LUCC. Human well-being is a key goal for societies, driving modifications in land use policies and the implementation of regulations on carbon emissions and energy usage. Low carbon emissions are a critical aspect of human well-being and represent the future direction of development.

There are still some limitations on this work. This article provides a preliminary conceptual framework and evaluation index system for the relationship between LUCC, CEs, and HW, without quantifying the complex relationship between them. The explorations on more specific topics, such as the carbon sink effects of unused land and water, are not in-depth enough. The concept of low-carbon human well-being introduced in this article serves as a preliminary assessment standard for gauging the synergy between human well-being and low-carbon initiatives in the future. It still requires more detail and in-depth improvement and refinement in the future work. To effectively diminish overall carbon emissions associated with enhancing human well-being and ensure sustained progress, it is crucial to investigate topics based on the framework proposed in this paper in more detail, for example, monitoring of different land uses and linkages between human well-being and carbon emissions from both natural processes and social activities. The evaluation index system urgently needs to be established as well, which would contribute to quantitative studies scrutinizing the prevailing developmental trajectories across various nations and territories. It can help to identify the most suitable development model, offering valuable insights for relevant future research.