Abstract. Robust appraisals of climate impacts at different levels of global-mean temperature increase are vital to guide assessments of dangerous anthropogenic interference with the climate system. Currently, two such levels are discussed in the context of the international climate negotiations as long-term global temperature goals: a below 2 °C and a 1.5 °C limit in global-mean temperature rise above pre-industrial levels. Despite the prominence of these two temperature limits, a comprehensive assessment of the differences in climate impacts at these levels is still missing. Here we provide an assessment of key impacts of climate change at warming levels of 1.5 °C and 2 °C, including extreme weather events, water availability, agricultural yields, sea-level rise and risk of coral reef loss. Our results reveal substantial differences in impacts between 1.5 °C and 2 °C. For heat-related extremes, the additional 0.5 °C increase in global-mean temperature marks the difference between events at the upper limit of present-day natural variability and a new climate regime, particularly in tropical regions. Similarly, this warming difference is likely to be decisive for the future of tropical coral reefs. In a scenario with an end-of-century warming of 2 °C, virtually all tropical coral reefs are projected to be at risk of severe degradation due to temperature induced bleaching from 2050 onwards. This fraction is reduced to about 90 % in 2050 and projected to decline to 70 % by 2100 for a 1.5 °C scenario. Analyses of precipitation-related impacts reveal distinct regional differences and several hot-spots of change emerge. Regional reduction in median water availability for the Mediterranean is found to nearly double from 9 to 17 % between 1.5 °C and 2 °C, and the projected lengthening of regional dry spells increases from 7 % longer to 11 %. Projections for agricultural yields differ between crop types as well as world regions. While some (in particular high-latitude) regions may benefit, tropical regions like West Africa, South-East Asia, as well as Central and Northern South America are projected to face local yield reductions, particularly for wheat and maize. Best estimate sea-level rise projections based on two illustrative scenarios indicate a 50 cm rise by 2100 relative to year 2000-levels under a 2 °C warming, which is about 10 cm lower for a 1.5 °C scenario. Our findings highlight the importance of regional differentiation to assess future climate risks as well as different vulnerabilities to incremental increases in global-mean temperature. The article provides a consistent and comprehensive assessment of existing projections and a solid foundation for future work on refining our understanding of warming-level dependent climate impacts.
The wave of national net zero CO2 and greenhouse gas emission targets could, if fully implemented, reduce best estimates of projected global average temperature increase to 2.0-2.4°C by 2100 and could bring achievement of the Paris Agreement within reach. 131 countries are discussing, have announced, or have adopted net zero targets, which together cover 72% of global emissions. Together, these net zero targets could significantly lower projected global warming compared to currently implemented policies (2.9 to 3.2°C) or to the pledges submitted to the Paris Agreement (2.4 to 2.9°C). MainAnalyses of current promises and actions by countries to limit climate change have concluded that they are by far insufficient to meet the goal of the Paris Agreement to limit global temperature increase to well below 2°C, while pursuing efforts to limit it to 1.5°C (refs. [1][2][3][4][5] ). Specific policies employed to reduce emissions in line with the Paris Agreement may differ from country to country. However, a chief requirement of collective action is codified in Article 4.1 of the Paris Agreement (Article 4.1, UNFCCC, 2015): emissions need to peak as soon as possible and anthropogenic emissions must be balanced by removals in the second half of the century. In other words, global emissions must reach a net zero level. The idea to include a global net zero target in the Paris Agreement was put forward in the run up to its adoption in 2015. 7,8 Pathways to meet this goal have been evaluated in the literature subsequently 9 .
The adoption of the 1.5°C long‐term warming limit in the Paris Agreement made 1.5°C a “hot topic” in the scientific community, with researchers eager to address this issue. Long‐term warming limits have a decade‐long history in international policy. To effectively inform the climate policy debate, geoscience research hence needs a core understanding of their legal and policy context. Here we describe this context in detail and illustrate its importance by showing the impact it can have on global carbon budget estimates. We show that definitional clarity is essential on this important matter.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.