Fifth assessment report by the IPCC

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The Fifth Assessment Report ( English Fifth Assessment Report , AR5 , also Fifth IPCC Assessment Report ) of the Intergovernmental Panel on Climate Change ( Intergovernmental Panel on Climate Change , IPCC) of the United Nations was published in 2014/2015.

The reports of the IPCC regularly summarize the current state of scientific knowledge about the influence of mankind on the earth system ( anthropogenic influence) and the resulting feedback (natural influence). Climate change plays a major role here, i.e. the projected consequences of changed Earth system parameters such as the global mean surface temperature or the amount of precipitation . The current AR5 provides the basis for most environmental and climate-related decisions for the international community.

The sixth assessment report of the IPCC will be prepared from 2017.

The progress reports of the IPCC

The Intergovernmental Panel on Climate Change (IPCC, Intergovernmental Panel on Climate Change , the Germans often IPCC ) was established in November 1988 by the Environmental Program of the United Nations  (UNEP) and the World Meteorological Organization  established (WMO), an intergovernmental institution into being in order for policy makers to summarize the state of scientific research on climate change without giving recommendations for action.

The main task of the committee is to compile the scientific basis and the global state of research on the effects of climate change and its risks as well as mitigation and adaptation strategies and to evaluate them from a scientific point of view. To this end, the IPCC appoints thousands of scientists from all over the world. These create the “status reports” of the IPCC. So far, the IPCC has published five status reports and more than ten special reports as well as guidelines for the preparation of greenhouse gas inventories .

Publication of the AR5

The summary ( Summary for Policymakers ) of the results of Working Group I ( The Physical Science Basis ) for the fifth world climate report was published on September 27, 2013; a final draft ( Final Draft ) of the full report on September 30, 2013, the editorial edited final version on January 30, 2014.

The presentation of the summary of the report by Working Group II ( Impacts, Adaptation and Vulnerability ) on March 31, 2014 in Yokohama was accompanied by an urgent appeal by the chairman of the IPCC, Rajendra Pachauri , for more climate protection and broad media coverage. The German federal government reaffirmed the climate target of reducing CO 2 emissions by 40 percent by 2020 compared to 1990 levels.

The report of Working Group III ( Mitigation of Climate Change ) was presented on April 13, 2014 at a press conference in Berlin. The Summary For Policymakers was published parallel to the press conference , the Technical Summary and the individual detailed chapters followed on April 15, 2015.

The synthesis report was published on November 2, 2014. In total, more than 830 scientists were directly involved as authors of the 5th assessment report , and several thousand researchers also took part in the scientific assessment of the report.


The report of Working Group I comprises 2216 pages and consists of a comprehensive technical summary (127 pages), an introduction, thirteen content chapters and three appendices. The Summary for Policymakers is 36 pages long and includes an introduction and the sections “Observed changes in the climate system”, “Drivers of climate change”, “Understanding the climate system and its current changes”, “Future global and regional climate changes”. The current UN climate report is based on the Fourth Assessment Report, into which new results have been incorporated. 9,200 peer-reviewed studies are cited in the bibliography .

In order to document scientific uncertainty, the statements (in all parts of the report) were either assessed qualitatively by the team of authors (“very low” to “very high” confidence) or - if possible - quantitative probabilities were given. These range from "almost certain" (99-100% probability) to "very likely" (90-100% probability), "likely" (66-100% probability) to "extremely unlikely" (0-1% probability) . Where applicable, statements were also presented as facts (without specifying probabilities).

see main article: Handling Uncertainty in the IPCC Process

Main knowledge of working group I "Physics-Scientific Basics"

To understand the attributes used in the following as likely , great confidence , etc. See Article treatment of uncertainties in the IPCC process .

Observed changes in the climate system

A warming of the climate system is clear: the atmosphere and the ocean have become warmer, snow and ice have decreased, the sea level and the concentration of carbon dioxide in the atmosphere have increased. Changes with strength since the 1950s have not yet occurred on time scales from decades to millennia.

  • The average temperature of the earth's surface rose by 0.85 ° C from 1880 to 2012.
  • It is likely that in the northern hemisphere, 1983 to 2013 was the warmest 30-year period in 1,400 years.
  • Extreme weather events such as heat waves are very likely to have become more frequent and longer lasting.
  • It can be assumed with great confidence that between 1971 and 2010 , the oceans absorbed 90% of the additional energy from global warming . The layers near the surface of the water heated up the most . In the upper 75 meters, the temperature rose by an average of 0.11 ° C per decade from 1971 to 2010. The top 700 meters almost certainly warmed up from 1971 to 2010.
  • It is believed with great confidence that the Greenland Ice Sheet and the Antarctic Ice Sheet have lost mass over the past two decades. The mass loss from 2002 to 2011 was 215 billion tons / year for the Greenland ice sheet and 147 billion tons / year for the Antarctic ice sheet. The world's glaciers very likely lost 275 billion tons of ice per year between 1993 and 2009.
  • The extent of the Arctic sea ice in the summer very likely decreased by 9.4 to 13.6 percent per decade, which corresponds to 730,000 to 1,070,000 km².
  • The north polar snowpack has been decreasing since the middle of the 20th century ( great confidence ).
  • The rise in sea ​​level between 1901 and 2010 was 19 ± 2 cm. It is likely that the increase has accelerated since the early 20th century; from 1993 to 2010 the increase was very likely 3.2 mm / year.
  • The current concentration of greenhouse gases in the atmosphere is the highest in 800,000 years. Human activities have released 555 billion tons of carbon since 1750; Compared to the pre-industrial concentration, the carbon dioxide content has increased by 40%. The rate of increase in the concentration of greenhouse gases in the 20th century was very likely to be the highest in the past 22,000 years. 155 billion tons of the released carbon was taken up by the ocean; the pH of the top layer has decreased by 0.1 (corresponding to an increase in hydrogen ions of 26 percent, great confidence ).

Drivers of climate change

The radiative forcing of the climate system has increased by 2.29 watts / m² compared to the year 1750; atmospheric CO₂ makes up the largest part of this .

  • The share of changes in solar radiation is only 0.05 watt / m² and, like volcanic eruptions, only had a small share in the climate changes in the last century.
  • It is extremely likely (> 95%) that human influence is the main driver of global warming observed since 1950 .

Future global and regional climate changes

The NASA video shows temperature and precipitation simulations for the 21st century. It is based on the four CO₂ concentration paths of the 5th assessment report with the increase in the CO₂ content in the air to 421  ppm ( RCP 2.6 ), 538 ppm (RCP 4.5), 670 ppm (RCP 6.0) and 936 ppm (RCP 8.5) up to the year 2100. The color differences show the change in the average temperature of the individual years compared to the globally observed temperature changes of the years 1971–2000. (in HD , English)
Diagram of the representative concentration paths for CO₂ mixture ratios up to the year 2100

The further release of greenhouse gases will lead to further global warming and the associated changes to the climate system. The estimation of future climate change based (Engl. On the use of climate models on four concentration paths representative concentration pathways (RCPs), " representative concentration pathways "). These represent the results of new emission scenarios, including, for the first time, a scenario that takes ambitious climate protection measures into account (RCP 2.6). The paths are named after the change in radiative forcing which, compared to the state in 1750, would go hand in hand with them by about 2100: RCP 2.6 - change in radiative forcing 2.6 W / m², RCP 4.5 - 4.5 W / m² , RCP 6.0 - 6 W / m² and RCP 8.5 - 8.5 W / m².

  • Regardless of the concentration path, the temperature of the earth's atmosphere will likely be 0.3–0.7 ° C higher between 2016 and 2035 than between 1985 and 2005.
  • The further rise in temperature depends on the concentration path : for the period 2081 to 2100 it will probably be between 0.3–1.7 ° C (RCP 2.6) to 2.6–4.8 ° C (RCP 8.5).
  • It is almost certain that weather extremes will increase.
  • Extreme rainfall in mid-latitudes and humid tropical regions is likely to become more frequent and intense.
  • The ocean will continue to warm, the heat will move down from the upper water layers and affect ocean currents. It is very likely that the Atlantic meridional overturning circulation (AMOC) (which includes the Gulf Stream ) will weaken. A collapse or relocation in the 21st century is very unlikely , but cannot be ruled out later if the temperature continues to rise.
  • With the concentration path RCP 8.5 (further increase in greenhouse gas emissions), the Arctic Ocean is likely to be ice-free in the summer before the middle of this century.
  • The volume of glaciers will decrease by between 15–55% (RCP 2.6) and 35–85% (RCP 8.5) by the end of this century ( medium confidence ).
  • The sea level is likely to rise between 26–55 cm (RCP 2.6) and 45 to 82 cm (RCP 8.5) by the period 2081–2100, depending on the concentration path. In the latter case, the increase will be 98 cm by 2100 ( medium confidence ).
  • The collapse of ice sheets could lead to an additional rise of several tens of centimeters.
  • It is almost certain that the rise in sea level will continue for a few hundred years after 2100, simply because of the thermal expansion of the water. With a further increase in the concentration of carbon dioxide in the atmosphere, the increase can be more than three meters by 2300 ( medium confidence ).

Understanding the climate system and its current changes

Observations, investigations of feedback and simulations with climate models contribute to our understanding of the climate system.

  • The climate models have been further developed and are able to simulate long-term climate changes well.
  • For shorter time periods (from 10 to 15 years) and at the regional level, which are more influenced by random events, the climate models are less reliable.
  • Doubling the amount of carbon dioxide in the atmosphere would warm the earth by 1.5–4.5 ° C ( great confidence ).

Further information

Climate models

The new climate simulations, on which the statements about future climate changes in the AR5 are essentially based, were partially carried out in the Coupled Model Intercomparison Project Phase 5 ( CMIP5 ), an international collaboration of the Climate Model Community. The 2009 publication A Summary of the CMIP5 Experiment Design describes the details of the coordinated experiments.

Secondary summaries

The core messages in German were summarized and published jointly by the Federal Environment Ministry , the Federal Ministry of Education and Research , the German IPCC Coordination Office and the Federal Environment Agency .

Main findings of Working Group II "Consequences, Adaptation, Vulnerability"

According to Working Group I, human interventions in the climate system lead to climate change. This represents a risk for human and natural systems. The contribution of Working Group II examines how patterns of risks and potential benefits change through climate change, how climate change-related consequences and risks can be managed through adaptations and climate protection.

  • The consequences of climate change can already be observed globally. Ocean warming, for example, is a striking example of global warming. Since 1971 the water temperature of the top 75 m has risen by an average of 0.11 ° C every ten years.
  • future consequences and risks: changed precipitation distribution, ocean acidification and much more. The development of precipitation shows an increase in the tropics and middle latitudes of the northern hemisphere and a decrease in arid regions of the subtropics. Since the middle of the 20th century, heat waves have occurred more frequently, particularly in Europe, Asia and Australia, and heavy rain events have increased in frequency and intensity both in Europe and in North America. The development of precipitation and that of extreme weather will show an increase in the current trend in the future.

Oceanic systems

  • The ecosystems of the oceans show changes due to climate change and will show further changes in the future depending on the speed, strength and duration of climate change ( almost certainly ). Mankind depends on the benefits of marine ecosystems, which are sensitive to climate change ( highly informative ).
  • Climate change changes the physical, chemical and biological properties of the oceans ( very informative ).
  • The geological data, current field research and laboratory tests confirm the connections between the most important environmental drivers and the corresponding impacts of marine ecosystems and climate change ( highly informative ).
  • The vulnerability of most organisms to warming is determined by their physiology. This defines limited temperature ranges and their thermal sensitivity ( high significance ).
  • The warming-related changes in occurrence, geographical distribution, migration behavior and seasonal activity of species ( very high informative value ) were and are accompanied by a reduction in their maximum body size ( medium informative value ). This has and will lead to changed interactions between species, including competition and prey-hunter dynamics ( high informative value ).
  • As a consequence of a further warming of 1 ° C or more by the middle of the 21st century and beyond, ocean-wide changes in ecosystem properties will occur and according to the forecast will continue ( highly informative ).
  • By the middle of the 21st century, the change in the distribution of species diversity will result in increased species diversity in the temperate and high latitudes ( high informative value ) and reduced species diversity in the tropics ( medium informative value ). This will change the catch potential of fish and invertebrates and affect food safety in the tropics ( medium informative value ).
  • The net primary production (NPP) will decrease globally, depending on the RCP scenario ( medium informative value ). With the RCP8.5 scenario, the estimated reduction will be up to 9% by 2100 (relative to 1990, medium informative value ).
  • Large-scale processes and climatic feedbacks that are maintained by microbes ( bacteria , archaea , unicellular algae and protozoa ) play a decisive role in marine ecosystems (e.g. storage of carbon and nitrogen and nutrient cycle ) and are changed by climate change ( medium informative value ).
  • Rising CO 2 (carbon dioxide) concentration over the last century and into the future will not only lead to ocean warming, but also change the carbon chemistry of the oceans, this is known as ocean acidification ( Ocean acidification ). Effects of acidification range from changes in physiology and behavior to population dynamics ( medium to high informative value ) and will affect marine ecosystems for centuries if the emissions persist ( high informative value ).

Main findings of working group III "Climate protection"

  • Without additional efforts, the global average temperature will rise by 3.7 to 4.8 ° C by the year 2100 compared to pre-industrial levels.
  • If the CO 2 concentration in the atmosphere does not rise above 450 ppm, it is likely that the global mean temperature will not rise by more than 2 ° C. This requires substantial reductions in global greenhouse gas emissions.
  • The commitments made at the UN Climate Change Conference in Cancun to avoid greenhouse gases by 2020 are inconsistent with the corresponding long-term scenarios, according to which an increase in the global average temperature of more than 2 ° C is at least as likely as an increase of less than 2 ° C .
  • The global energy supply must be restructured quickly and fundamentally. Central to this is no longer to burn coal to generate energy (see also: coal exit ).

Although Working Group III includes authors from different disciplines and schools, the central parts of the report are shaped by a neoclassical-economic perspective. Some authors who belonged to Working Group III of the IPCC, such as Matthew Paterson from the University of Ottawa, criticize that such a view is not in a position to think about the abrupt social changes that climate change brings with it or makes necessary.

Web links


Secondary summaries

Individual evidence

  1. Claim: "The IPCC is a political organization", accessed on December 30, 2016.
  2. History of the IPCC ( Memento of the original from January 18, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed December 29, 2016 @1@ 2Template: Webachiv / IABot /
  3. ^ The Intergovernmental Panel on Climate Change (IPCC): Website of the German IPCC Coordination Office , accessed on April 12, 2019.
  4. Publication and Data , accessed on December 29, 2016.
  5. IPCC publishes full report Climate Change 2013: The Physical Science Basis , press release January 30, 2014, accessed February 4, 2014.
  6. Report of the Intergovernmental Panel on Climate Change - Presentation of the summary of Part II in Yokohama ( Memento from April 1, 2014 in the Internet Archive ) In: , March 31, 2014, accessed on March 31, 2014.
  7. ↑ Intergovernmental Panel on Climate Change urgently calls for action. In: Die Welt , March 31, 2014, accessed on March 31, 2014.
  8. Synthesis report : Climate Change 2014 - Synthesis report with long version and summary for Policymakers , accessed on November 2, 2014
  9. Mojib Latif : Are we getting the climate out of sync? , in: Klaus Wiegandt (Ed.), Courage for Sustainability. 12 ways into the future . Frankfurt am Main 2016, 80–112, p. 100.
  10. Summary for Policymakers - Introduction
  11. Graham Readfearn: IPCC climate change report by numbers. In: The Guardian . September 27, 2013, accessed September 27, 2013 .
  12. IPCC AR5 WG1: Summary for policymakers . 2013.
  13. Working Group I, Technical Summary (2013), p. 44.
  14. CMIP5 Coupled Model Intercomparison Project. In: WCRP World Climate Research Program. Retrieved October 15, 2013 .
  15. ^ Karl E. Taylor, Ronald J. Stouffer, Gerald A. Meehl: An Overview of CMIP5 and the Experiment Design . In: Bulletin of the American Meteorological Society . tape 93 , no. 4 , October 7, 2011, ISSN  0003-0007 , p. 485-498 , doi : 10.1175 / BAMS-D-11-00094.1 .
  16. ^ German IPCC coordination office: Key messages of the IPCC reports in the fifth reporting cycle, 2008-2014 . These are brief explanations in German of the most important messages of the IPCC reports of the fifth reporting cycle in order to make it easier for the interested public to access the extensive results of the IPCC. These are not literal translations, the wording of the texts published by the IPCC is decisive.
  17. IPCC (Ed.): Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Committee on Climate Change . Assessment and management of the risks of climate change ( [PDF]).
  18. Key messages of the Fifth Assessment Report of the IPCC Climate Change 2013: Scientific Basics (Partial Report 1). Federal Ministry for the Environment, Nature Conservation and Nuclear Safety; Federal Ministry of Education and Research; German IPCC Coordination Office, Federal Environment Agency, May 30, 2016, accessed on July 9, 2016 .
  19. ^ IPCC, Working Group 3, Summary for Policymakers
  20. Marcel Hänggi: "In the parallel world of climate economists", Die Wochenzeitung, October 8, 2015