Optimal Timing of Greenhouse Gas Emissions Abatement in Europe

Round 1

Reviewer 1 Report

Dear authors

First congratulations, I found your work very interesting, clear in the purposes and executed with a methodology can be easily adapted for the EU as average or for the single countries. I agree with the authors in highlighting the urgency to design long term policies: short term goals can be achieved saving “waste of energy” or behaving “wiser”, but a net zero emissions society needs infrastructural changes that, as the authors' highlight, take time.

Just a few comments:

1. The author said the work is focused on non ETS, anyway the roadmap 2050 goal (-80-95%) also include the ETS sectors, so just clarify that achieving the 2050 goal (figure 2a) for non ETS doesn’t mean the achievement of the roadmap 2050 (even ETS looks a less weak measure than non ETS regulation). In this regard, I would include a citation of the roadmap 2050, for instance: European Climate Foundation the Roadmap 2050 Project. Available online: http://www.roadmap2050.eu/reports (accessed on 14 November 2018).

2. Regarding lines 27-28. In many works, the Paris Agreement is cited as the most important climate warming target should not be surpassed to grant the less damage possible to our ecosystem. Anyway, are the policies elaborated by the authors, or even the roadmap 2050 goals, really in line with the COP 21 goal? COP 21 target refers to “carbon budgets” compatible with a global warming of a certain temperature (1.5°C, or 2°C or higher), while trajectories concern the abatement rates of GHG, but they don’t assess the cumulative rise of the GHG in the atmosphere (the GHG concentration) that instead is responsible, as the authors discuss in 210-212, of the damage costs. Net zero emissions in 2050 are ambitious, but there is no evaluation of how much EU (or a single country) has burnt along to the path to go there. Thus, there is no direct connection with the global policy of the COP21 and the EU ongoing policy as discussed for instance in the work of Perissi et al. (- Sustainability- (2018) Potential European Emissions Trajectories within the Global Carbon Budget. : 1–13.). I suggest the authors could add the carbon budget undergone their abatement curves for non ETS, or at least discussed briefly the limits of their approach in the frame of the COP 21 target.

Author Response

Thank you for your constructive comments.

Regarding point 1, we have provided a clarification in lines 302-305 of the revised manuscript (text above Figure 1); this includes a reference to ECF's Roadmap Report (new reference [15]).

Regarding point 2, we take the current EU policy as granted, therefore, in line with your second suggestion, we highlight the limits of our approach with regard to the COP21 target (see lines 390-397 of the revised manuscript, second paragraph before the last one of the paper).

Reviewer 2 Report

This is a solid paper. The research question is clear: the relationship between 2030 and 2050 abatement targets & costs in achieving decarbonization. The methods are clearly laid out. The results are clear and have important, timely implications for both researchers and policymakers - current EU-wide targets for 2030 are insufficient for achieving 2050 goals and need to be strengthened. I recommend this paper for publication and have only two comments to help improve it:

the methods and data sections are rather dense - suggest moving some of it to an SI, or placing these sections at the end of the paper, after the discussion/conclusion;

Is there a particular sector that is most at risk if initial policy steps are weak for meeting stronger 2050 goals?

Author Response

Thank you for your constructive comments. 

- On your first comment: We have shortened the methodology section and moved all equations and detailed information about the modle to an Appendix.

- On your second comment, we have added a sentence at the end of hte second paragraph of the concluding section (lines 381-383 of the revised manuscript), which explain the sectors that are most at risk of not meeting 2050 emission reduction goals.