After two weeks of online consultations with representatives from almost every country in the world, the Intergovernmental Panel on Climate Change (IPCC) of the United Nations presented the first of four partial reports for the sixth assessment report on climate change this morning and increased the pressure on climate policy.

If greenhouse gas emissions are not reduced “immediately, quickly and on a large scale”, it says, the goal of limiting global warming to 1.5 degrees or at least two degrees compared to pre-industrial times is out of reach.

Joachim Müller-Jung

Editor in the features section, responsible for the “Nature and Science” section.

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Working group one of the IPCC does not even have a mandate to deal with political goals and debates. Rather, their task was to bring even more clarity into the physical processes of global warming and, seven years after the fifth assessment report, to lay the foundations for the consequences and possible measures against climate change worked on in two other IPCC working groups. More than 14,000 specialist publications were evaluated by more than 230 experts from all over the world.

The conclusion: There is even more certainty about the causes and consequences of global warming: It is now "undeniable" that humans have a hand in their emissions and that there is "trust in the statements made by climate research" continued to grow, according to the German co-author of the report, the Hamburg Max Planck researcher Dirk Notz.

And: Man-made climate change is now "observable in every region of the world and in the entire climate system".

Change "unprecedented" for hundreds of years

The Intergovernmental Panel on Climate Change sees the new analysis as a relentless “reality check for climate change”; Long-standing uncertainties regarding the sensitivity of the climate could be significantly reduced. With a view to the regional changes that global climate change will bring about in the next few decades, the sixth IPCC report made it possible for the first time to make more reliable statements that could be used for risk assessments and planning of climate adaptations down to the regional level.

For the time being, only the 42-page “Summary for Political Decision-Makers”, which is relevant to climate policy, was presented to the public from the 400-page long working group report. In contrast to the status report itself, it is the result of an intergovernmental process of negotiation on formulations which, in the end, both climate scientists and diplomats have to unanimously agree. The scientific state of knowledge and the projections of climate change derived from computer models for the next decades are outlined in the document with the underlying scientific uncertainties and in each case explained how likely certain developments can occur.

The IPCC is now very certain that the acceleration of global warming is not only man-made, but that many of these changes are historically "unprecedented for hundreds, if not thousands of years".

Ocean warming irreversible

Since the beginning of industrialization, the earth has warmed up by a good 1.1 degrees on average, and the number of heat waves in the oceans has almost doubled in forty years - which is a heavy burden on the oceans and coral reefs around the world. Among the irreversible changes that will probably not be reversible in the next few centuries, the IPCC counts the recently significantly accelerated rise in sea level due to ice melting, especially in the polar regions and in the alpine glaciers, as well as the warming of the oceans.