9. August 2021
The Intergovernmental Panel on Climate Change publishes the Sixth Assessment Report of Working Group I

World cli­mate re­port – cli­mate change in­ten­si­fies weath­er and cli­mate ex­tremes

2021 flood disaster in Germany
2021 flood dis­as­ter in Ger­many
Image 1/3, Credit: DLR-ZKI (CC BY-NC-ND 3.0)

2021 flood disaster in Germany

Ex­treme weath­er and cli­mate events are oc­cur­ring more fre­quent­ly due to hu­man-in­duced cli­mate change. In Ju­ly 2021, pro­longed heavy rain­fall caused dev­as­tat­ing floods in west­ern Ger­many as well as in neigh­bor­ing Eu­ro­pean coun­tries. DLR sup­port­ed the emer­gen­cy ser­vices and civ­il de­fense au­thor­i­ties with the rapid pro­duc­tion and anal­y­sis of satel­lite da­ta and aeri­al pho­tographs of severe­ly af­fect­ed ar­eas. This DLR aeri­al im­age shows the view from a he­li­copter fly­ing over the Eifel re­gion on 16 Ju­ly 2021. Ac­cord­ing to the lat­est re­port of the In­ter­gov­ern­men­tal Pan­el on Cli­mate Change (IPCC), heavy pre­cip­i­ta­tion and flood­ing in Eu­rope will be­come more in­tense if glob­al warm­ing reach­es 1.5 de­grees Cel­sius.
Changes in glob­al sur­face tem­per­a­ture
Image 2/3, Credit: IPCC, Figure SPM.1

Changes in global surface temperature

The rate at which glob­al sur­face tem­per­a­ture has warmed due to hu­man ac­tiv­i­ty is un­prece­dent­ed in at least the last 2000 years of Earth’s his­to­ry.The left-hand graph shows tem­per­a­ture changes over the past 2000 years. The dark gray line de­notes val­ues re­con­struct­ed us­ing pa­le­o­cli­mat­ic archives from year one to year 2000. The black line shows the ob­served warm­ing from 1850 to 2020. The val­ues are decade-av­er­aged and rel­a­tive to 1850-1900.The graph on the right shows ob­served tem­per­a­ture changes over the last 170 years – com­pared to cli­mate mod­el cal­cu­la­tions. The mea­sured da­ta (black line) are an­nu­al av­er­ages, rel­a­tive to the years 1850-1900. The col­ored ar­eas show the re­sults of the CMIP6 cli­mate mod­el sim­u­la­tions. The light brown ar­eas show the cal­cu­lat­ed warm­ing due to hu­man caus­es and nat­u­ral fac­tors. This cli­mate sim­u­la­tion agrees well with sci­en­tif­ic ob­ser­va­tions. The green ar­eas show how the glob­al sur­face tem­per­a­ture would have evolved if on­ly nat­u­ral caus­es were con­sid­ered, such as so­lar or vol­canic ac­tiv­i­ty. The com­par­i­son of the sim­u­la­tions and ob­ser­va­tions clear­ly shows that hu­mans are main­ly re­spon­si­ble for the warm­ing of the cli­mate sys­tem.
Results of the IPCC report
Re­sults of the IPCC re­port – hu­mans have warmed the cli­mate
Image 3/3, Credit: German Climate Consortium

Results of the IPCC report – humans have warmed the climate

The find­ing of the IPCC Sixth As­sess­ment Re­port, re­leased on 9 Au­gust 2021, is that hu­man ac­tiv­i­ties have warmed the at­mo­sphere, oceans, and land sur­faces. Widespread and rapid changes have oc­curred in the at­mo­sphere, oceans, land and bio­sphere. Ob­ser­va­tion­al da­ta and im­proved mod­el cal­cu­la­tions in the new IPCC re­port clear­ly con­firm this once again.
  • Intergovernmental Panel on Climate Change has released a new report – AR6 Climate Change 2021: The Physical Science Basis.
  • Human activities are largely responsible for global warming and climate change.
  • Unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to 1.5 degrees Celsius will be beyond reach.
  • DLR scientists contributed to the new IPCC assessment report as authors.
  • Focus: Climate change, Earth observation, space, air transport

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.”

Significance of the IPCC climate reports

The Intergovernmental Panel on Climate Change (IPCC) (IPCC) is a body of the United Nations (UN). At regular intervals, it commissions leading experts to compile the latest findings from climate research and assess them from a scientific perspective in the form of reports. The IPCC assessment reports provide a foundation for science-based decision-making without giving policy recommendations. They are of great importance in international politics and at world climate conferences. The Summary for Policymakers (SPM) created for each of the reports is discussed by the IPCC member countries at the approval plenary. The governments involved can propose wording for this summary – the authors then check whether these suggestions are consistent with the statements in the underlying report. By approving the summary and accepting the report, the member governments endorse the statements made in the summary and acknowledge that they are applicable.

The first of a total of three volumes of the Sixth Assessment Report has now been published, dealing with the physical science basis of climate change. As part of Working Group I, over 230 authors from 66 countries have assessed and summarised more than 14,000 scientific publications on climate research.

National points of contact

The German IPCC Coordination Office was set up at the DLR Projektträger in 1998 by the Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung; BMBF) and the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit; BMU). It supports them and acts as a point of contact with the IPCC for government bodies, the research sector and the public. The coordination office promotes the transfer of knowledge between climate research and climate policy and, together with partners, provides German translations of the most important IPCC publications. Experts from the DLR Project Management Agency review drafts of IPCC reports on a regular basis.

The German Climate Consortium (Deutsches Klima Konsortium; DKK) brings together key players in national climate research and climate impact research, whose work helps to identify climatic changes and point out possible courses of action for prevention and adaptation. The DKK provides summary information and further explanations on the reports published by the IPCC. On the DKK website, Professor Veronika Eyring and two other authors of the current world climate report speak briefly and comprehensibly about the new findings and explain the climate simulations of the IPCC report.

  • Bernadette Jung
    Com­mu­ni­ca­tions Ober­paf­fen­hofen, Weil­heim, Augs­burg
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 8153 28-2251
    Fax: +49 8153 28-1243
    Münchener Straße 20
    82234 Weßling
  • Prof. Dr. Veronika Eyring
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of At­mo­spher­ic Physics
    DLR In­sti­tute of At­mo­spher­ic Physics, Earth Sys­tem Mod­el Eval­u­a­tion and Anal­y­sis
    Münchener Straße 20
    82234 Oberpfaffenhofen


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