*4.1. Climate Changes and Potato Yield and Productivity*

Climate change is having an increasingly strong impact on agriculture, but there is no unanimity in the scientific community and there is still no clarity on the directions of this impact. Earlier forecasts of the impact of climate change on the agricultural economy were more radical and assumed very rapid changes. One of such early forecasts was made in 1991 at the Institute of Soil Science and Plant Cultivation in Puławy on the basis of the General Circulation Model developed by the Goddard Institute for Space Studies. According to this model, climate changes were to be beneficial for agriculture and to bring an increase in the yields of all crops, except for potatoes, after 2020, and to significantly increase the area of maize and soybean cultivation [33]. The last two forecasts were confirmed, the others, unfortunately, were not. It was assumed that the growing season would significantly extend, which would allow for the extension of the assortment of arable crops and the improvement of animal production efficiency. This optimism resulted from the prediction of an increase in the average annual air temperature by 3 ◦C, an extension of the growing season by about 30–40% and an increase in the average amount of rainfall from 625 to 1100 mm [33]. It is now known that such a scenario is not realistic. Recently, the prevailing view is that, on a general scale, the expected changes in the form of global warming will bring beneficial effects in the agricultural economy of Europe. According to most authors [34–43], the production potential of agriculture was supposed to increase, but unfortunately in the case of potatoes, this scenario did not work. Our research, carried out on the basis of the results of the Central Statistical Office and COBORU research in southeastern Poland show that, in the last 20 years, both the yield, area and harvest of potatoes decreased. The reasons for this condition are manifold. Tomczyk et al. [44] proved that, in Poland, in the last 20 years, there was a significant increase in Tmax in the summer period. This shows, inter alia, for the ten warmest years in the analyzed period, mainly after 2000. The consequence of the increase in Tmax is the increase in the frequency of hot days. A further increase in the number of hot

days in Poland is forecast in the coming decades. The smallest changes are predicted for the areas with the most intense changes in Tmax. Agriculture is a sector that is particularly vulnerable to the effects of climate change, and climatic factors are important factors in the success of agricultural production. Therefore, the effects of climate change already have a negative impact on the food security of society [45,46]. The Climate Coalition (CC) report "The impact of climate change on Poland's food security" warns that if Poland does not achieve the goals of the Paris Agreement and stops the increase in the average global temperature below 2 ◦C, the food security of citizens at the global level, regional and local will be increasingly threatened. Therefore, both the reduction in greenhouse gas emissions and multi-directional adaptation measures in agriculture are necessary.

According to the reports of the Agricultural Drought Monitoring System in Poland [47], in the years 2009–2011, there was a significant risk of drought in potato crops. In the years 1983–2002, the level of precipitation during the potato growing season reached the optimum only in five of the twenty years studied [35,47,48], and the losses of tuber yield in Poland for this reason ranged from 7% to 45% [47]. The high acclimatization capacity of crops may turn out to be a disadvantageous phenomenon, as it was associated with significant energy expenditure on the reconstruction of structures and adapting their functions to stressful conditions, which results in a reduction in agricultural yields [12,34,38,39,49]. In research on plant productivity, the decline in agricultural yield is often used as a measure of the possibilities of the studied cultivars for the stress syndrome occurring during the growing season. Under such assumptions, the yield is the resultant of many different mechanisms responsible for the diverse sensitivity of plants to environmental stresses, and each of these mechanisms may work differently under specific environmental conditions. The approach that takes yield loss as a measure of resistance may be useful for the final evaluation of the effectiveness of breeding treatments and has a greater selection value than the resistance criteria [38]. The research results presented in the paper concern issues related to the reaction of potatoes to the diversified course of meteorological conditions during the potato growing season and are based on numerous figures from the period of 20 years (2000–2019), taken from several sources (Central Statistical Office, Provincial Statistical Office, Institute of Meteorology and Water Management, and Experimental Stations of the Central Research Center for Cultivated Plants). These results prove that climate change in this period had a significant impact on all the studied economic, meteorological and physiological-natural features.

Precipitation is the most sensitive element of climate changes and that changes in time and space. According to Kalbarczyk [39], no permanent trend has taken place over the last 500 years. This period was subject to much thermal continentalism than it is today. According to the calculations of the Sadowski continentalism index [50], it was found that in Eastern Europe, the warmest century was the 11th century, and in Western Europe, it swas the 20th century, while the coldest centuries were in the 15th and 12th centuries, respectively. From the fifteenth century, the degree of continental climate in Poland remained at a high level until the nineteenth century. Average annual air temperatures in winter were much lower, by approximately 1.5–3.0 ◦C, compared to the present situation, while summer temperatures were higher than today by 0.9–1.5 ◦C. Over the past 100 years, Earth has warmed by 0.85 ◦C, and the speed of this process is increasing. In Europe, the temperature has risen by almost 1 ◦C.

The impact of climate change on world agriculture can be considered in two main aspects: natural and socio-economic. The first is direct, and the second is indirect, usually resulting from the former. The changes in the natural basis of the agri-environmental economy relate primarily to the greenhouse effect associated with an increase in the concentration of carbon dioxide in the atmosphere. The main cause of the rapidly following climate change is the increase in carbon dioxide (CO2) content in the atmosphere, causing the so-called greenhouse effect. This will enable some cereal crops, such as wheat or rice, as well as potato plants to photosynthesize more intensively and, consequently, result in faster development with higher yields [50–53]. It was assumed that, as a result, increasing

plant production may reduce the specter of hunger but only in the case of organized international activities. It is generally known that areas of hunger are concentrated in the poorest countries, where climatic conditions generally pose problems for proper farming. It is primarily the dry zone of Africa and some regions of Asia [54]. According to Kulig [5] and Ziernicka-Wojtaszek [6,7], the optimism related to the increase in plant production as a result of the increase in CO2 in the atmosphere was, however, premature. These authors propose that the influence of carbon dioxide concentration in the atmosphere on the global agricultural production should be considered in direct and indirect categories. The former concerns the intensification of photosynthesis and the possibility of plant development with lower water resources and their more effective use. Indirect impacts should be seen in the aspect of climate and soil changes, as well as in the development of diseases and pests. In the case of direct impacts, our research indicates a very large differentiation in the increase in yields resulting from the increase in the carbon dioxide content, but under natural conditions. Laboratory experiments confirm that plants absorbing more carbon grow faster and are larger [39]. Moreover, the increased concentration of carbon dioxide increases the efficiency of water use. This applies in particular to plants of the so-called C3 group (e.g., wheat, rice, soybean and potato), which show, under conditions of increased CO2 content, an increased photosynthesis rate and a moderate decrease in transpiration. On the other hand, plants from the C4 group (maize, sugar cane, sorghum, etc.) show relatively slower photosynthesis (slower biomass growth) under these conditions [5,49].

Repeated droughts and desertification on almost all continents already threaten the livelihoods of some 1.2 billion people [4]. For example, an increase in CO2 from 330 to 660 ppm (parts per million—gas particles per million air particles per unit volume) resulted, under optimal conditions, in an increase in cotton yield due to the concentration of carbon dioxide. The main conclusion of physiological studies [49] is the fact that the positive effect of an increase in CO2 than twice lower than other important environmental factors (humidity and thermal conditions, the content of mineral nutrients and another) can counteract this influence. The concentration in laboratory conditions on plant production is not confirmed under the conditions of natural plant cultivation.

The research of many authors [5–7,35–37,51–53] shows that the most likely scenario will be a slow temperature increase resulting from an increase in the concentration of carbon dioxide in the atmosphere. The result will be a shrinkage of cool climate zones and an expansion of hot climate zones. The effects of the temperature rise will be more pronounced in areas near the poles than in the equatorial areas. Therefore, the shift in climatic zones will be more marked in higher latitudes. In regions with a temperate climate, such as Central and Eastern Europe, the shift by 1 ◦C will be from 200 to 300 km [54]. This will have a direct impact on the extension of the range of some crops, including sweet potatoes [12].

The production potential will increase mainly in the temperate climate zone. Global changes in world agriculture under the influence of climatic changes will cause many processes in the natural environment that are still difficult to identify. They will also shape socio-economic processes and phenomena. The considerations to date show that the greatest increase in production possibilities will take place in the most economically developed countries, where problems with food overproduction are observed. On the other hand, in the poor countries of Africa and Asia, where there are hunger zones, there may be growing food problems resulting from reduced production possibilities [54]. The increase in the production potential of agriculture in rich countries will result in an increase in the average global agricultural production per unit area. There is still a problem of food overproduction in the European Union countries, which the Common Agricultural Policy is trying to mitigate and eliminate. One of the directions of activities is the widely understood extensification of agricultural production, including the reduction in the area of land developed by agriculture [7,50].

Europe and North America have relatively ample room to adapt to the effects of climate change. The research conducted so far shows that there will be rather favorable

changes in terms of agricultural production possibilities. However, in subtropical regions (e.g., in southern Europe), large areas may be exposed to drought, while on the continents of the Americas, the risk of extreme phenomena will increase: floods, droughts and cyclones. The warming of the climate will cause the extension of dry areas also to the areas of Southern Europe and the necessity to take decisive measures in the field of water retention and the irrigation of farmland [45,50,54].

Global climate change poses a serious challenge to global food security. The sensitivity of germs, potentially toxin-producing microorganisms and other pests to climate factors, shows that climate change can affect the incidence and intensity of certain food-borne diseases.
