On Monday 9 August the IPCC launched its Summary for Policymakers of the Working Group I contribution to the Sixth Assessment Report (Climate Change 2021: The Physical Science Basis). This high-level summary delivers the most up-to-date and comprehensive assessment of the climate system and climate change. The new report explains that it is now certain that observed increases in atmospheric greenhouse gases since 1750, and the observed global warming that has occurred over the same period, are caused by human activities. Average global temperatures over the last decade are thought to be higher than those of the most recent geological warm period (which was 6500 years ago). Changes in global sea level, where rises of more than 2m by the year 2100 cannot be ruled out, and other changes in the ice-ocean system are likely to be irreversible for centuries.
The new report goes further than previous IPCC publications in linking extreme events – such as heatwaves and extreme rainfall – to anthropogenic climate change. This so-called ‘attribution science’ unravels the contributions of human-induced climate change and natural variations for a range of weather events. For example, human-induced climate change is likely to be the main driver of increased heavy rainfall events over many areas since the 1950s (in IPCC language, ‘likely’ means a 66% or greater chance, and ‘main driver’ means responsible for more than half the changes). It is also thought likely that human-induced climate change has increased the chance of compound extreme events, where multiple hazards threaten society and the environment (e.g. hot, dry and windy conditions increasing the risk of wildfire).
Future projections of climate change from climate models, were derived using five new greenhouse gas emissions and land use scenarios (‘Shared Socio-economic Pathways’, or SSPs) which range from very high emissions to scenarios where carbon dioxide emissions reduce to net zero around 2050. Concerningly, under all scenarios, there is more than a 50% chance that the lower goal of the Paris agreement (1.5°C) will be exceeded by 2040. The projections also show that the 2°C goal of the Paris agreement will be exceeded by the year 2100 unless significant reductions in emissions are made in the coming decades.
The report contains strong messages and guidance for regional adaptation planning. Climate model projections show that every region will experience multiple increases in climatic impact-drivers with future warming (climatic impact-drivers are the physical conditions that affect people or ecosystems). Each degree of global warming will increase the frequency and intensity of extreme events like heatwaves, droughts, and extreme rainfall, and changes in many of these will be more widespread for 2°C compared to 1.5°C of global warming. A heatwave event that occurs on average once every ten years now would be twice as frequent, and also more severe, with global warming of 2°C. Even with 1.5°C of global warming, there is high confidence that heavy rainfall and associated flooding will increase in most regions of Africa and Asia. Alongside their new findings, the IPCC have produced an online Interactive Atlas that allows adaptation planners to understand and interpret the latest climate science (IPCC WGI Interactive Atlas) and develop effective adaptation climate actions.
The IPCC AR6 Summary for Policymakers provides the strongest evidence yet that human activities are causing climate change and making extreme weather events more frequent and more severe in every part of the world. The result that very small differences in future temperature can massively amplify extreme events is a powerful reminder of why we must strive to meet the goals of the Paris agreement. The careful analysis of the new report, which explores a wide range of socio-economic futures, also provides the basis for some optimism. The very worst effects of climate change can still be avoided if we act immediately to enhance global ambition for both mitigation and adaptation. In November, leaders from 196 countries will meet in Glasgow for the COP26 summit with the aim of agreeing upon action to limit climate change and its effects. As the President for COP26, Alok Sharma, recently announced, “We can’t afford to wait two years, five years, ten years – this is the moment”. COP26 is the unique opportunity for world leaders to take the necessary urgent and far-reaching action before it is too late.