The recent 6th Assessment Report of Working Group I of the Intergovernmental Panel on Climate Change (IPCC) is the result of years of diligent assessment of the latest scientific evidence on climate change building on several previous similar assessments. It was written by hundreds of authors, and openly reviewed by thousands of experts. Every word of the Summary for Policymakers was agreed by all 195 parties to the UNFCCC and at COP26.

The report is clear that the world has warmed by around 1.1°C since the industrial revolution, and that this is due to human activities, primarily burning fossil fuels. As a direct consequence, heatwaves and heavy rainfall events have become more frequent and more intense. As the oceans have warmed and the ice sheets have melted, sea levels have risen, increasing the risk of coastal flooding. Our past greenhouse gas emissions have caused changes of the climate which have harmed both human society and ecosystems.

We are at a crossroads.

The global choices being made now determine what happens to the climate next.

A pathway of immediate, strong, rapid, sustained and large-scale reductions in greenhouse gas emissions would hold global warming to well below 2°C. If emissions are halved by 2030 and reach net-zero by around 2050 then there is a reasonable chance of limiting warming to 1.5°C. Such reductions in greenhouse gas and particulate emissions would also bring additional benefits through slowing ocean acidification and improving air quality.

Reaching net-zero emissions will halt global warming but, for some consequences, there is no going back. For example, sea level will continue to rise for centuries but the rate of change can be slowed through emission reductions. There is a small chance that sea level rise could rapidly accelerate if the Antarctic ice sheet is less stable than anticipated and every bit of warming increases the risk of this and other unexpected events.

For over 150 years the scientific community has understood the theory of how adding additional greenhouse gases to the atmosphere would warm the planet. Global warming was first observed and linked to rising carbon dioxide levels in the 1930s, and the IPCC assessed that there was a discernible influence of human activity on the rise in temperatures in 1995.

In 2021, the scientific community has again assessed the latest evidence from theory, measurements, and state-of-the-art simulations of our planet. We are certain that human actions have changed the climate and that we are already experiencing the consequences, especially though changes to extreme weather.

Every further tonne of greenhouse gas added to the atmosphere raises the planet’s temperature and makes the climatic consequences more severe. Each country faces different risks from the changing climate and every bit of warming avoided in future will limit those risks. Improving resilience and adapting to the ongoing changes will also reduce further suffering.

The global choices being made now matter, for all of us and for many generations to come.

Or in very short form:

If we choose not to act,
Or fail to adapt,
Then suffer we will.

Note: this is my personal summary of the science contained in IPCC AR6 WGI and the implications.