Is the climate crisis perhaps coming much sooner and in a far more dramatic form than previously thought? – About the first part of the CMIP6 report of the Intergovernmental Panel on Climate Change (IPCC)

All over the world, scientists are conducting research on climate issues. In order to be able to better compare the many different versions of climate models that have been developed and to coordinate research efforts, the international Coupled Model Intercomparison Project CMIP was launched in the mid-1990s by the World Climate Research Programme WCRP. The CMIP models have been developed over the course of the last almost 30 years with ever increasing complexity and quality – i.e. accuracy. Thus, in recent years, the sixth model class (CMIP6) with the AR6 report was awaited with the greatest excitement (although much of it had already been published in advance). Its publication (that of the first group, with a second to follow) finally took place on 9 August 2021.

Some interrelationships, for example global cloud formation and the interaction of the atmosphere with the oceans, had long been inadequately calculated. It repeatedly revealed new feedbacks, the effects of which are now, with AR6, somewhat better understood – although still not perfectly. With global warming and the melting of ice, for example, the salt water content in the oceans is changing. This change influences ocean currents, but how this effect can be calculated exactly and what other temperature effects this triggers is now somewhat better known, but still not very precise. The climate models of the CMIP6 series have addressed these problems much more intensively, but future CMIP series will have to address them in more detail and other open problems.

The CMIP6 models are once again much more ambitious in their demands for model accuracy than their predecessors. For example, in some of them the spatial resolution of the grids on which the global climate is modelled has been brought to below 100 kilometres. This makes it easier to capture the effects of cloud formation on the local and global climate. At the same time, the temporal density of the measurements increases significantly.

“This report is invaluable for future climate negotiations and policy makers,” said IPCC President Hoesung Lee of South Korea. Erich Fischer, a climate researcher at the Swiss Federal Institute of Technology (ETH) Zurich and one of the IPCC lead authors, put it somewhat more dramatically: “The climate state has continued to change rapidly, and the window of opportunity to meet the goals of the Paris Agreement is gradually closing.” What is significant about the report is that compared to the negotiations on the AR5 publication almost eight years ago, the debates seem to have gone much more smoothly. The IPCC authorship probably clearly prevailed this time against the resistance from politicians against clear formulations that had always taken place before. Moreover, the scientific nature of the report was no longer touched. Responsibility is now also clearly stated: According to the IPCC, humans are clearly responsible for all observed global warming since pre-industrial times (1.6 degrees on land, 0.9 degrees over the sea, 1.1 degrees as a global average)!

Their overall result is more staggering than most people expected. Thus, the increase of the global average temperature by 1.5 degrees compared to the pre-industrial level, which, after all, should not be exceeded as far as possible according to the Paris Agreement, could already be reached earlier than previously assumed and with a high probability already in the early 2030s, if the emission of greenhouse gases is not drastically reduced. In the IPCC Special Report of 2018, the estimate of when the 1.5 degrees will be reached under these conditions was between 2030 and 2052. Today, the estimate of the very latest date is 2040. The global community is thus likely to miss the Paris targets by a huge margin if greenhouse gas emissions do not fall faster and more drastically, according to the report.

The publication of the report coincided with catastrophic weeks of flooding in Germany and Switzerland, extreme heat in Canada and the north-west of the USA, heat records in northern and southern Europe, massive fires in Turkey, and severe flooding in China. All this – and especially the simultaneity of all these events – would not have been possible without the heat records, according to the consensus of climate researchers. Extremely hot days will increase significantly in all parts of the world without exception. At the same time, it will become more likely that heat waves and droughts or heavy rain and storms will occur simultaneously. It is also clear to climate researchers that we will most likely exceed the critical two-degree limit if we do not reduce greenhouse gas emissions to zero or close to zero before the middle of the century. To many people this seems to be too polemical of a statement. But in the sciences, it is simply not allowed to see the world as politicians, economists and many others would like it to be. Rather, scientists show us how it really is. And it is by no means the first time in history that they have experienced public resistance.