Recently, a network of climate model groups showed that it will cost more to exceed the temperature targets of the Paris Agreement than to stay on a low-temperature trajectory. That same day, that collaboration also published work which shows that additional overshoot risks stem in part from consequent increases in extreme weather conditions. These studies are two of the four published this year; together they provide the most comprehensive projections of the requirements and implications of the path we take to reach our end-of-the-century temperature targets.
The article focused on the economics of meeting the Paris temperature targets, specifically how much mitigation actions will cost and the impact on global GDP, it was not designed to project environmental impacts. In fact, most economic models do not include this level of complexity and, as a result, they underestimate the overall costs. But this additional analysis projects not only how much extreme weather will increase, but also how that will affect crop yields around the world.
“The decarbonisation scenarios reviewed by the Intergovernmental Panel on Climate Change (IPCC) in the latest assessment reports do not take into account feedback from climate impacts. The main reason is that [there are] many uncertainties surround the geophysical and economic impacts of climate change, making it difficult to integrate them into decarbonization pathway design, ”wrote first author Dr. Laurent Drouet in an email to Ars Technical. Drouet is a researcher at the European Institute of Economy and Environment RFF-CMCC, in Milan, Italy. “But now, [our] research is focused on improving the representation of these impacts and producing results that are easier to integrate into mitigation models ”.
The general conclusions are similar: exceeding temperature targets will lead to more environmental damage and additional costs than projected by more economically focused models. This work also highlights the uneven burden of these consequences and which nations will be hit the hardest.
Extreme weather risks
Like related work, this study is part of the largest effort yet to systematically model the costs and benefits of limiting warming entirely. This compares with allowing temperatures to temporarily exceed the Paris targets and relying on massive carbon dioxide removal in the second half of the century to compensate. In this current articleResearchers specializing in modeling environmental effects took the lead, but the collaboration again projected future scenarios using nine assessment models, plus additional analysis to explore extreme weather effects in more detail.
There are a number of reasons why it might not be realistic or ethical to count on correcting the weather by the end of this century after exceeding temperature targets. But most models, and policy discussions, are based on going down that path. These two recent studies are part of a growing body of work showing the benefits of avoiding the need for correction in the first place.
In one of these analyzes, it was found that basic economic growth benefits from avoiding overshoot. But the economy doesn’t capture everything; The authors note that one reason for the prevalence of “overshoot” scenarios is that these models often do not incorporate the environmental benefits of minimizing extreme weather, such as its impacts on agriculture. With these included, the balance tips even further in favor of minimizing heat immediately.
Heat waves, drought and crop loss
The researchers projected the maximum effects on the duration and frequency of heat waves, the frequency of droughts, energy demands (for heating and cooling) and the loss of crops of corn, rice, soybeans and wheat. In all of these, there were negative impacts associated with each 0.1 ° C of warming. The overshoot scenarios were slightly worse than those that kept temperatures low, but the most important factor was keeping the overall temperature rise as low as possible.
The authors also added estimates from other recent studies to explore the relationships between temperature and GDP growth, and to reduce the projections to a regional (rather than global) level. From this analysis, they found that increases in heat waves had the most severe impact, and that they disproportionately affected Brazil and Western and Southern Africa.
“Tropical regions will suffer more than other regions with overheating, and their climate risk will increase much more, that is, overheating will allow the possibility of impacts of much greater amplitude in those regions,” Drouet wrote.
“The ultimate goal is to bring together the findings of the two IPCC working groups (WG2-Impacts and WG3-Mitigation),” Drouet added. “Our research starts this movement; and we show that if we take into account the impacts of excess temperature, the design of the mitigation pathways would instead favor the net zero emission pathways. “
The authors also note that this study aims to capture only some of the potential environmental effects, and as a result, they believe their projections likely still underestimate the economic impact. It may never be possible to explore all the tradeoffs with a single model, but by combining so many of these models with additional climate and damage analysis, this work combines some of the best tools available to scientists at this time.
Nature Climate Change, 2021. DOI: 10.1038 / s41558-021-01218-z