These findings are not surprising, but serious: Human activities are the primary cause of global warming and the observed climate change. Newly acquired data and improved model simulations provide even more evidence for this than before, as the Intergovernmental Panel on Climate Change (IPCC) emphasises in its new report. On 9 August 2021, the first volume of the IPCC Sixth Assessment Report was released. This report by Working Group I (WGI) summarises the state of research on the physical science basis of climate change. Scientists from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) contributed to the report as authors.
“Human activities are the main driver not only for the warming of the climate system, but also for the increase in weather and climate extremes. The frequency and intensity of heavy rainfall events and heat waves, for instance, are increasing due to climate change,” explains Veronika Eyring of the DLR Institute of Atmospheric Physics and the University of Bremen. She is coordinating lead author of the chapter called ‘Human influence on the climate system’ in the new IPCC Assessment Report, which also includes the evaluation of climate models with observational data.
Climate changes in the atmosphere, the ocean and the cryosphere are continuing to reach new highs and are occuring at rates that are unprecedented over centuries, or even millennia. “The atmospheric concentration of carbon dioxide had already risen to a total of 410 parts per million (ppm) by 2019, meaning that there are 410 molecules of carbon dioxide in every million molecules of dry air. This is unprecedented for at least the last two million years,” Eyring points out.
DLR is therefore already actively working on solutions to reduce emissions. In the ECLIF2 project, for example, DLR scientists were able to show that the use of sustainable fuels already noticeably reduces soot emissions and thus the climate impact of air traffic in the short term.
Climate consequences for Europe
For Europe, climate change leads to generally warmer weather and increasing risk of heavy rainfall in many regions – there is less frequent, but more intense rainfall. The devastating effects this can have were visible most recently in July 2021 with the flood disaster in Germany. Such extreme events will increase in frequency, especially if global warming exceeds 1.5 degrees Celsius.
The report also suggests that temperatures in all European regions will continue to rise and exceed the average global temperature change.
Evaluation of the simulations
In order to present the results of the evaluation of climate models with observations, some chapters of the IPCC report use the Earth System Model Evaluation Tool (ESMValTool). The DLR Institute of Atmospheric Physics is leading the development of this tool, working together with more than 70 international research institutions. The computer program allows a comprehensive evaluation of climate and Earth system models in comparison with observational data. Climate models are computer programs based on scientific principles that simulate the Earth’s physical climate system. Earth system models take into account chemical and biological processes in addition to climate. With the help of the ESMValTool, the results can be presented in a comprehensible and reproducible way.
Using the ESMValTool, the simulations of the latest generation of global climate models, which are coordinated within the framework of the World Climate Research Programme’s ‘Coupled Model Intercomparison Projects Phase 6’ (CMIP6), were evaluated and assessed in the report. “We were able to show that the simulated climatological averages for many large-scale climate variables have improved compared to previous model generations,” says Eyring, who led the CMIP6 project from 2014 to 2020. CMIP6 simulations, along with observational data, are an important source of climate information for the IPCC report.
Eyring was awarded the Gottfried Wilhelm Leibniz Prize 2021 for her significant contribution to improving the understanding and accuracy of climate projections through process-oriented modelling and model evaluation. In her research, the DLR scientist focuses on Earth system modelling and model evaluation with observational data, including the development and application of artificial intelligence methods for reliable climate projections and technology assessments.
Global warming – human causes
It is unequivocal that human activities have warmed the atmosphere, oceans and land surfaces. Widespread and rapid changes have occurred in the atmosphere, ocean, land and biosphere. Observational data and improved climate models in the new Assessment Report clearly confirm this once again.
The extent to which climate change has already progressed is revealed by new findings from the Arctic. In contrast to previous IPCC reports, it is now clear that there will probably be virtually no sea ice at the end of some summers in the future. Global surface temperatures have now warmed by about 1.09 degrees Celsius (2011 to 2020) compared to pre-industrial times (1850 to 1900). Each of the past four decades has, in turn, been warmer than any previous decade since 1850, and globally averaged surface temperatures have increased even faster since 1970. This recent rate of warming is unprecedented for at least 2000 years.
“Many changes in the climate system become larger in direct relation to increasing global warming. The challenge now is to reduce greenhouse gas emissions immediately, rapidly and drastically. Otherwise, limiting warming to 1.5 degrees Celsius compared to the pre-industrial period will be out of reach,” Eyring adds. In all five scenarios of the report, global warming will reach this level with a probability of more than 50 percent in the next 20 years.
“For more than 30 years, the Intergovernmental Panel on Climate Change, as an institution of the United Nations, has published its assessment reports on the state of the global climate. The facts from these renowned publications provide a foundation for science-based alternative courses of action for policymakers. With its capabilities in space-based Earth observation and the use of research aircraft, DLR is actively contributing to the emergence of a comprehensive database,” explains Anke Kaysser-Pyzalla, Chair of the DLR Executive Board. “More than ever, we need the evaluation of climate data in order to assess the consequences of human influence on climate. The synergies between DLR’s research areas enable us to develop technologies for climate-friendly mobility. This includes sustainable transport concepts as well as research into new, renewably based energy sources.”