The United Nations Intergovernmental Panel on Climate Change has delivered a comprehensive report on the state of global climate science, only the sixth such report in the last 30 years.

The report provides new estimates of the chances of crossing the global warming level of 1.5C in the next decades, and finds that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5C or even 2C will be beyond reach.

The IPCC predicts that strong and sustained reductions in emissions of carbon dioxide and other greenhouse gases would limit climate change, with the benefits for air quality coming quickly, but even with these measures it could take 20 to 30 years to see global temperatures stabilise. Furthermore, the report warns that some of the changes already set in motion—such as continued sea level rise—are irreversible over hundreds to thousands of years.

The report shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1C of warming since a baseline of 1850-1900. This assessment is based on improved observational datasets to assess historical warming, as well progress in scientific understanding of the response of the climate system to human-caused greenhouse gas emissions.

“This report is a reality check,” said IPCC Working Group I co-chair Valérie Masson-Delmotte. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”

However, the report also warns of a myopic focus on temperature, as changes to wetness and dryness, to winds, snow and ice, coastal areas and oceans will intensify the water cycle. This brings more intense rainfall and associated flooding, as well as more intense drought in many regions; rainfall patterns are also affected, with high latitudes seeing an increase in precipitation.

Coastal areas will see continued sea level rise throughout the 21st century, contributing to more frequent and severe coastal flooding in low-lying areas and coastal erosion and further warming will amplify permafrost thawing, and the loss of seasonal snow cover, melting of glaciers and ice sheets, and loss of summer Arctic sea ice. Changes to the ocean, including warming, more frequent marine heatwaves, ocean acidification, and reduced oxygen levels have been clearly linked to human influence. These changes affect both ocean ecosystems and the people that rely on them, and they will continue throughout at least the rest of this century.

For the first time, the Sixth Assessment Report provides a more detailed regional assessment of climate change, including a focus on useful information that can inform risk assessment, adaptation, and other decision-making, and a new framework that helps translate physical changes in the climate – heat, cold, rain, drought, snow, wind, coastal flooding and more – into what they mean for society and ecosystems.

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