IPCC Fourth Assessment Report

The Fourth Assessment Report (English: Fourth Assessment Report, AR4 ) of the Intergovernmental Panel on Climate Change (Intergovernmental Panel on Climate Change, IPCC) of the United Nations is the report from 2007, which summarizes the state of scientific knowledge on global warming regularly. The current report is Fifth Assessment Report of the IPCC, which began publication in September 2013. The issued at intervals of five to six years IPCC reports are widely regarded as a consensus position within the climatological experts when it comes to the human influence on climate. Previous reports published in 1990, 1995 and 2001 (Third Assessment Report, Third Assessment Report, TAR).

On 2 February 2007, the Summary for Policymakers ( Summary for Policymakers ) Working Group I ( Working Group I) on the " Scientific Foundations " (Physical Science Basis ) following a conference in Paris was released. The summary of the report of Working Group II followed on " Impacts, Adaptation and Vulnerability " ( Impacts, Adaptation and Vulnerability) on 6 April, the Working Group III on " Mitigation of Climate Change " ( Mitigation of Climate Change) on 4 May 2007. A summary of the full report ( "Synthesis band" ) was released on November 17, 2007.

  • 2.1 PBL report

Results of the working groups

Working Group I: " Scientific Basis "

The report of the Working Group I is concerned with the physical basis of climate change. It gives an overview of the mid-2006 dominant understanding of the natural sciences, as is evident from the relevant scientific literature. Among other things, the changes in atmospheric composition, knowledge of related past climate changes ( paleoclimate ), climate models and their predictions, the observed changes in nature due to global warming and the determination of the underlying environmental factors are treated in eleven chapters.

A total of 1043 different scientists from 48 different countries and 7 international organizations cooperated in this part report. Among them are 152 lead authors, 498 contributing authors, 26 review editors, and 626 reviewers, although some people have been involved in several chapters in various roles. Overall, were cited by the authors and editors over 6,000 peer -reviewed articles and more than 30,000 comments the reviewer considered. The Summary for Policymakers was approved by the governments of 113 countries.

The report highlights enhances the role of man in the currently observable climate change. The energy balance of the climate system is altered by changes in the concentration of greenhouse gases and aerosols in the atmosphere, the nature of the land surface and sunlight. The quantitative estimates of the respective influence ( see Figure ) have improved since the Third Assessment Report. The most important cause of global warming is with a specified probability of more than 90 percent "very likely" the greenhouse gas carbon dioxide ( CO2), the human emissions; followed by the less important gases methane ( CH4), nitrous oxide (N2O ) and other. And the other factors of lesser importance, including the natural variations in solar activity.

The average temperature of the lower atmosphere in the centennial linear trend 1906-2005 by 0.74 ° C ( ± 0.18 ° C) increase ( the corresponding value from the Third Assessment Report for the period 1901 to 2000 was still at 0.6 ° C (± 0.2 ° C)). Eleven of the last twelve years ( the years 1995-2006) rank among the twelve warmest years since the beginning of the nationwide temperature measurements in 1850., The trend of the past 50 years, is measured with a warming of 0.13 ° C (± 0.03 ° C ) per decade, almost twice as high as for the last 100 years.

The risks associated with this temperature rise of global warming, which lists the report, include a rise in sea level by 17 centimeters in the 20th century - since 1993 by 3.1 millimeters per year; melting glaciers, reducing the snow-covered surface by 5 percent since 1980, which in recent years significantly accelerated decline of sea ice; frequent heavy rain; increasing rain in northern Europe and eastern North and South America; increasing aridity in the Mediterranean, the Sahel, South Africa and parts of South Asia; increasing heat waves and violent tropical storms.

For the future, further increasing global warming is expected for the bandwidth of different scenarios are presented which operate with different assumptions such as population growth or economic growth. The resulting emission scenarios can be one of the four characteristic scenario families A1, B1, A2, B2 assign. The letters and numbers denote the scenario families: The letter A refers to business-oriented scenarios, the letter B environmentally oriented scenarios, the number 1 scenarios with a focus on global development and the number 2 scenarios with a focus on regional development. See also the accompanying table, which represents the combination of these scenario families.

The A1 scenario family is divided into the three listed below scenario groups that describe alternative directions of technological change in the energy sector:

In the best scenario B1, the increase in average temperature is up to the Decade 2090-2100 1.8 ° C ( with a likely range of 1.1-2.9 ° C), in the worst case A1fl 4.0 ° C ( 2.4 -6.4 ° C). In higher latitudes, the temperature is expected to rise faster than near the equator.

The sea level rises, according to the scenarios used by the end of the 21st century by at least 18-38 cm and a maximum of 26-59 cm, with some complicated assumptions about the future behavior of the ice sheets were used. The report specifically points out that the models currently in use do not include the full impact of the changes in the Eisschildflüsse as well as uncertainties in climate - carbon cycle - feedback, since the time of the reporting lacked appropriate basis in the published literature. A higher sea level rise can not be ruled out.

Working Group II: " Impacts, Adaptation and Vulnerability"

Working Group II presented the current state of knowledge on the effects of climate change together. These include both the already discernible effect on the environment and likely future impacts.

Already, many have visible consequences. These include the decline of the ice and snow cover in the cold regions of the world, which lead numerous glacial lakes and bigger and glacial-fed rivers more water. Spring ( and with it events such as leaf unfolding and bird migration ) starts earlier and earlier; shifts in the distribution areas of animal and plant species are. poleward or to higher altitudes of the mountains Of the 29,000 evaluated data rows have more than 89 percent to a result that one would expect for a global warming; Changes accumulate there, where temperatures have risen the most. Therefore, natural causes for the changes to be very unlikely to occur (probability <10 percent).

Compared to the Third Assessment Report, the knowledge about future impacts of climate change have increased. It is expected that there is more precipitation at high latitudes and humid tropical areas; however, is less in dry regions. Both floods caused by heavy rains and droughts will increase. Thus, the adaptability of many ecosystems is overwhelmed; the damage will be negative impacts on biodiversity and the services provided by ecosystems services have ( such as water supply). Droughts and floods will reduce food production, especially at low latitudes, thus it comes about in Africa and some regions of Asia to increasing hunger. Particular risks will be exposed such as mangroves and the coastal and coastal ecosystems. From flooding due to rising sea millions of people will be affected, especially in the mega-deltas of Asia and Africa and on small islands. Human health is also directly affected, such as by increasing diarrheal diseases due to flooding and the spread of pathogens.

The regional distribution of impacts is also better known. Be particularly affected Africa and Asia have, especially in poor countries the means for protection are missing. Africa is particularly affected by food shortages, flooding in Asia under the great river deltas.

Adaptation measures are indispensable even in the best of climate change since the release of greenhouse gases already in the next century will still lead to a further warming of about 0.6 ° C. The range of measures ranging from technological measures (such as structures for coastal protection ) of behavioral changes (such as resource-efficient consumption) up to policy measures (such as planning decisions ); alone measures to adjust but can not control the effects of climate change.

Working Group III, " Mitigation of Climate Change "

Working Group III summarized the current state of research on technical, economic and social aspects of climate change. It is essentially about the technical and economic potential for emission reductions to potential policy responses to climate protection and the connection between sustainability and climate change.

Emissions of greenhouse gases are 1970-2004 increased by 70 percent; that of the main greenhouse gas, carbon dioxide, by about 80 percent. The highest proportion of this increase had the power supply ( 145 percent ) and transport ( 120 percent). If the current policy is not changed, we can by 2030 - depending on assumptions about economic and technological development - expect a further increase by 25 to 90 percent ( for carbon dioxide by as much as 45 to 110 percent).

However, there are a whole series of economic measures that could reduce the emission of greenhouse gases. What measures are economically depends on the price that attaches to one ton of carbon dioxide; 6 billion tons of carbon dioxide could be saved even by 2030 through measures that save money at the same time. There is a whole set of measures needed to reduce greenhouse gas emissions. The key measure or technology does not exist. A core area is the efficient generation, distribution and use; about through combined heat and power, renewable energy sources, replacing coal with gas, more efficient vehicles, lighting and power usage, better insulation and heat recovery; but this also includes measures such as the shift of traffic from road to rail, improved use of nitrogen fertilizer and better methods for rice farming in agriculture and ( re) afforestation and use of forest products as a replacement for fossil fuels. The expansion of nuclear power will be limited by the IPCC 's view, because of security concerns, the danger of nuclear proliferation and the unsolved waste problem.

Other technologies will be commercially viable in the coming decades, as second-generation biofuels, solar power cheaper and better renewable energy sources. The measures by which the concentration of greenhouse gases would be limited to a level that the temperature would have to rise by more than 2 to 2.4 ° C would reduce the annual global economic growth by 0.12 percent in the most expensive case - but with significant regional differences. These costs are the result of costs of climate change and other benefits, such as reduced air pollution, over. To achieve this goal yet, the reversal in the emission of greenhouse gases by 2015 at the latest would be initiated.

By 2050, the emissions of greenhouse gases by 50 to 80 percent would decrease if the temperature rise is to be limited at 2 to 2.4 ° C. In addition to energy efficiency will play mainly carbon-free energy sources and the capture of carbon dioxide from the flue gases of power plants play a role; that costs reflected in the long term the above 0.12 percent of economic growth.

The main instrument of climate policy is for the IPCC a price for greenhouse gas emissions - see emissions trading. Already a rate of 20 to 50 U.S. dollars per ton would make a lot of action on climate change economically; Subsidies for fossil fuels for climate protection were harmful. Governments could encourage with tax breaks or strict standards, the efficient use of energy; Technology transfer helps to allow other countries to use modern technology.

Climate protection is an integral part of sustainable development; and sustainable development helps the climate, for example by protecting forests. With lower emissions of air pollutants and more efficient use of energy, climate protection improves human health and increase the security of energy supply. But there can also be conflicts or trade-offs between objectives, for example, between climate change and sustainability (eg: the cultivation of crops for energy production can be at the expense of food security ). Here compromises are necessary in order to avoid problems; Goals must be operationalized.

Synthesis tape

The band synthesis summarizes the evaluations of individual working groups and provides an integrated view of climate change as the final part of the Fourth Assessment Report. Accordingly, the main findings of the report:

Is no doubt, receipts are rising temperatures, widespread melting of snow and ice and rising sea levels by global warming.

Global warming has already discernible impact on many natural systems, such as the previous spring commencement or directed towards the poles or to higher elevations change of the habitat of animal and plant species.

The causes of global warming are very likely (probability > 90 percent ) in the human-induced increase in the concentration of greenhouse gases in the atmosphere. The concentrations of carbon dioxide and methane are not only far higher than before the onset of industrialization, but also higher than in the last 650,000 years of Earth's history. From 1970 to 2004, the emissions of greenhouse gases have increased by 70 percent, the. Carbon dioxide by 80 percent

In the continuation of the current policy, the concentrations of greenhouse gases will continue to rise. How strong, the concentrations depends on the assumptions about economic and technological developments that have been studied in various scenarios. The range of possible consequent increase in temperature by the end of the 21st century is 1.1 to 6.4 ° C.

The possible consequences include, among other things, increasing weather extremes such as hot days, heat waves and heavy rain. Tropical storms are violent; at high latitudes increases the amount of precipitation, in widths from niederigen. Semi-arid areas will suffer from increasing water shortage. Be particularly affected Africa be (severe impairments of agriculture in many countries) and Asia ( flooding in the heavily populated mega-deltas ).

The warming would go even with constant greenhouse gas concentrations even after the end of the 21st century on, because even find set in motion changes in the climate system only after centuries to a new equilibrium. This also applies to the rise in sea level, its long-term extent is not yet be quantified. The same applies to the possible occurrence of abrupt or irreversible effects.

Adaptation to climate change can and must be improved; Adaptation alone is not sufficient to cope with the consequences, especially the possibilities for adaptation are regional differences. Especially the regions most affected are least able to protect themselves.

However, there are numerous possibilities, the actual heating by action on climate change less to maintain than calculated in the scenarios. The key technology in the fight against climate change are those based on energy efficiency and the use of lower carbon and free energy sources. To implement Governments can help by providing them the emission of greenhouse gases with a price; this makes the necessary measures rather economical. The cost of climate protection would meet even the most challenging objectives of a reduction in the average growth rate by more than 0.12 percent.


The fourth report of the IPCC was already before the first publication of the Summary for Policymakers subject of criticism, in particular because the summary for decision-makers before the actual report has been published, to customize the content of the report to the summary. This and other contents of the first publication to be criticized from various locations. So writes Spiegel Online that the report had lost its sharpness by political interference. In particular, the governments of the U.S., China, Russia and Saudi Arabia would have downplayed the anthropogenic contribution to the global warming and its possible consequences and thus make them look weaker than required by the scientists involved. The draft versions of the scientists, however, are documented in various places.

PBL report

In January 2010, it emerged that an indication of the melt of the Himalayan glaciers is wrong. Stood in the IPCC report that the Himalayan glaciers would melt by 2035 completely. The source used was a study from the 1990s, which stated that non-polar glaciers would melt by 2350. A Dutch journalist took place in the same month, also a second error: The area (26%) was under threat in the Netherlands by a rising sea level, was reported to be 55% too high because the risk of flooding by the Rhine and Meuse (29%) was miteingerechnet. However, took over for this error, the Dutch environmental agency PBL responsibility. She had the IPCC sent the text from which came the statement in error. The PBL explicitly stressed that one could make the IPCC lead authors no allegation that they relied on the statements of the Authority.

The Dutch Environment Minister Jacqueline Cramer asked for a parliamentary debate on 29 January, the PBL, a comprehensive assessment of ( listed in the synthesis Band) 32 make conclusions on the regional impacts of global warming and the underlying chapter of Working Group II. The published on 5 July 2010 PBL report came to the conclusion that the conclusions in the synthesis band would not be undermined by errors found. However, several conclusions contained statements that have no basis in the chapters or the sources cited there. Also isolated inadmissible generalizations and a lack of transparency and credibility of sources had occurred. Thus, the IPCC concluded by a decline in earnings in millet, groundnut and cowpea in Niger to declining crop yields in the Sahel, and from declining cattle productivity in Argentina due to declining livestock productivity in South America. Overall slight deficiencies in five, and severe defects in three of the 32 conclusions were noted.

In the analysis of each chapter on the regional impact another serious error was in addition to the errors concerned the Himalayas and the Netherlands found: The IPCC report is that the productivity of West African anchovy fisheries could be reduced by 50-60%. In the IPCC cited this source, however, is that extreme wind and water turbulence would decrease by 50-60%; Impact on the productivity of anchovy fisheries have not been quantified. In addition to six other minor errors and inaccuracies in the statements of PBL report came to some critical comments about the representations of individual matters. For example, criticizes that was - at the projected additional deaths not mentioned by heat in Australia, the impact of global warming underlying projections suggest a significant proportion of these deaths is caused by demographic changes alone.

The PBL report was the overall conclusion that the conclusions of the fourth IPCC report would continue to be permitted and a total well-founded. In addition to the errors has been criticized that in the summary of results of Working Group II in the synthesis band picked negative forecasts and positive forecasts had not been made without clarify this " risk-based " selection sufficient.