The Intergovernmental Panel on Climate Change (IPCC) announced the finalization of its Synthesis Report of the IPCC Sixth Assessment Report (AR6) during its 58th Session held in Interlaken, Switzerland, March 13-19, 2023. The IPCC also published a Summary for Policymakers (the Summary) in advance of the release of the Synthesis Report, as well as a Longer Report and a Presentation. The Synthesis Report integrates the main findings of the AR6 and provides an overview of the state of knowledge of climate change, its widespread impacts and risks, and climate change mitigation and adaptation.
The Synthesis Report has been highly anticipated and is the last of the Sixth Assessment Report products, due for release in time to inform the 2023 Global Stocktake under the United Nations Framework Convention on Climate Change. It provides an unprecedented level of scientific analysis and indicates that there are numerous, feasible, and effective options currently available to reduce greenhouse gas (GHG) emissions and adapt to human-caused climate change. Media reports from the New York Times emphasized that the Earth is likely to cross a critical global warming threshold by 2030 without rapid and drastic reductions in global GHG emissions. Reuters, quoting from the Summary, noted that “there is a rapidly closing window of opportunity to secure a livable and sustainable future for all”.
This bulletin briefly highlights key findings of the Synthesis Report included in the Summary.
The Summary is divided into the following three sections:
- Current Status and Trends, which covers the historical and present period.
- Future Climate Change, Risks, and Long-Term Responses, which addresses projected futures up to 2100 and beyond.
- Responses in the Near Term, which considers current international policy timeframes, and the time interval between now and 2030-2040.
Current Status and Trends. The Summary notes that:
- Human activities, principally through emissions of GHGs have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850–1900 in 2011–2020, increasing faster since 1970 than in any other 50-year period over at least the last 2000 years.
- In 2019, approximately 79% of global GHG emissions came from the sectors of energy, industry, transport and buildings together and 22% from agriculture, forestry and other land use (AFOLU).
- Climate change has caused substantial damages, and increasingly irreversible losses, in terrestrial, freshwater, cryospheric, and coastal and open ocean ecosystems with impacts on some ecosystems approaching irreversibility (hydrological changes resulting from the retreat of glaciers, changes in some mountain and Arctic ecosystems driven by permafrost thaw).
- Current global financial flows for adaptation are insufficient for, and constrain implementation of, adaptation options, especially in developing countries.
- Global GHG emissions in 2030 implied by nationally determined contributions (NDCs) announced by October 2021 make it likely that warming will exceed 1.5°C during the 21st century and make it harder to limit warming below 2°C.
- At least 18 countries have sustained absolute production-based GHG and consumption-based CO2 reductions for longer than 10 years; however, these reductions have only partly offset global emissions growth.
Future Climate Change, Risks, and Long-Term Responses. The Summary notes that:
- Cumulative carbon emissions until the time of reaching net-zero CO2 emissions and the level of GHG emission reductions this decade largely determine whether warming can be limited to 1.5°C or 2°C.
- Achieving and sustaining net negative global CO2 emissions, with annual rates of carbon dioxide removal (CDR) greater than residual CO2 emissions, would gradually reduce the warming level again.
- Deep, rapid, and sustained reductions in GHG emissions would lead to a discernible slowdown in global warming within around two decades, and also to discernible changes in atmospheric composition within a few years.
- Climatic and non-climatic risks will increasingly interact, creating compound and cascading risks that are more complex and difficult to manage.
- Hazards and associated risks expected in the near-term include an increase in heat-related human mortality and morbidity, food-borne, water-borne, and vector-borne diseases, and mental health challenges, flooding in coastal and other low-lying cities and regions, biodiversity loss in land, freshwater and ocean ecosystems, and a decrease in food production in some regions.
- Some future changes are unavoidable and/or irreversible but can be limited by deep, rapid and sustained global greenhouse gas emissions reduction.
- Adaptation options that are feasible and effective today will become constrained and less effective with increasing global warming.
- Above 1.5°C of global warming, ecosystems such as some warm-water coral reefs, coastal wetlands, rainforests, and polar and mountain ecosystems will have reached or surpassed hard adaptation limits and as a consequence, some Ecosystem-based Adaptation measures will also lose their effectiveness.
Figure SPM.5 from the Summary, reproduced below, provides an overview of global emissions pathways consistent with implemented policies and mitigation strategies.
Responses in the Near Term. The Summary notes that:
- The choices and actions implemented in this decade will have impacts now and for thousands of years.
- Deep, rapid and sustained mitigation and accelerated implementation of adaptation actions in this decade would reduce projected losses and damages for humans and ecosystems, and deliver many co-benefits, especially for air quality and health.
- Rapid and far-reaching transitions across all sectors and systems are necessary to achieve deep and sustained emissions reductions and secure a liveable and sustainable future for all.
- Mitigation and adaptation actions have more synergies than trade-offs with Sustainable Development Goals.
- Prioritizing equity, climate justice, social justice, inclusion and just transition processes can enable adaptation and ambitious mitigation actions and climate resilient development.
- Effective climate action is enabled by political commitment, well-aligned multilevel governance, institutional frameworks, laws, policies and strategies and enhanced access to finance and technology.
- Enhancing technology innovation systems is key to accelerate the widespread adoption of technologies and practices. Enhancing international cooperation is possible through multiple channels.
Figure SPM.7 from the Summary, reproduced below, provides an overview of mitigation options and the potential for demand-side mitigation options.
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