Documents Drouet, Laurent 3 results

"Mitigation pathways exploring end-of-century temperature targets often entail temperature overshoot. Little is known about the additional climate risks generated by overshooting temperature. Here we assessed the benefits of limiting overshoot. We computed the probabilistic impacts for different warming targets and overshoot levels on the basis of an ensemble of integrated assessment models. We explored both physical and macroeconomic impacts, including persistent and non-persistent climate impacts. We found that temperature overshooting affects the likelihood of many critical physical impacts, such as those associated with heat extremes. Limiting overshoot reduces risk in the right tail of the distribution, in particular for low-temperature targets where larger overshoots arise as a way to lower short-term mitigation costs. We also showed how, after mid-century, overshoot leads to both higher mitigation costs and economic losses from the additional impacts. The study highlights the need to include climate risk analysis in low-carbon pathways."

"Climate change and air pollution are two major societal problems. Their complex interplay calls for an advanced evaluation framework that can support decision making. Previous assessments have looked at the co-benefits of climate policies for air pollution, but few have optimised air pollution benefits. In our study, we lay out a modelling framework that internalises air pollution's economic impacts on human mortality, while considering climate constraints and aerosol feedback.
Methods
We developed a modelling framework based on an integrated assessment model (World Induced Technical Change Hybrid [WITCH]) designed to assess optimal climate change mitigation policies. We included structural and end-of-pipe measures in a detailed process integrated assessment model, that is hard-linked to air pollution and climate models. We analysed a large set of baseline scenarios, including five shared socioeconomic pathways (SSPs). SSP scenarios were also tested with three different levels of value per statistical life, and were combined with the Paris Agreement temperature targets (TTs), focusing on the 2°C and 1·5°C TTs by the end of the century.
Findings
We found that, in the baseline scenarios, where no policies are applied, the number of annual premature deaths grew before declining slightly to 4·45 (range 3·86–6·11) million annual premature deaths by 2050. Reaching the Paris Agreement TT decreases mortality by approximately 0·47 million premature deaths by 2050 (up to 1·28 million premature deaths in SSP3 –1·5°C) with respect to the baseline. We showed that welfare-maximising policies accounting for air pollution benefits reduces premature mortality by 1·62 million deaths annually. This is three times greater than the co-benefits of climate policies. China is the region where most of the avoided mortality is possible, whereas the reforming economies (ie, non-EU eastern European countries, including Russia) region has the greatest welfare benefits. We find that global and regional welfare increases when air pollution impacts are internalised, with no negative repercussions on global inequality."

"Climate stabilization pathways reviewed by the Intergovernmental Panel on Climate Change depict the transformation challenges and opportunities of a low carbon world. The scenarios provide information about the transition, including its economic repercussions. However, these calculations do not account for the economic benefits of lowering global temperature; thus, only gross policy costs are reported and discussed. Here, we show how to combine low carbon pathways' mitigation costs with the growing but complex literature quantifying the economic damages of climate change. We apply the framework to the scenarios reviewed in the Special Report on 1.5°C of the Intergovernmental Panel on Climate Change. Under a probabilistic damage function and climate uncertainty, we show that Paris-compliant trajectories have net present economic benefits but are not statistically different from zero. After mid-century, most scenarios have higher benefits than costs; these net benefits are most prominent in developing countries. We explore the robustness of results to an extensive set of damage functions published in the literature, and for most of the specifications examined, we cannot reject the null hypothesis of net benefits. Future research could improve these results with a better understanding of damage functions with greater coverage of damages and including adaptation and its cost."