Climate Change 2007, the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change (IPCC), is the fourth in a series of such reports. The IPCC was established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess scientific, technical and socio-economic information concerning climate change, its potential effects and options for adaptation and mitigation. Skeptics have made a variety of criticisms against the report.
The Fourth Assessment Report (Climate Change 2007) is released in four distinct sections:
For each section, the IPCC will release the main report and a summary version, known as the Summary for Policymakers. Full reports and summaries of Working Groups I-III have been released, plus a summary of the Synthesis Report.
The Working Group I Summary for Policymakers (SPM) was published on 2 February, 2007 and revised on 5 February, 2007. The full WGI report was published in March, and last updated on 5 September 2007. A 34-page Frequently Asked Questions document has been made available.
Climate Change 2007: The Physical Science Basis, the report of Working Group I, "assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change".
The report was produced by around 600 authors from 40 countries, and reviewed by over 620 experts and governments. Before being accepted, the summary was reviewed line-by-line by representatives from 113 governments during the 10th Session of Working Group I, which took place in Paris, France, between 29 January and 1 February 2007.
On the issue of global warming and its causes, the SPM states that:
Footnote 6 on page 3 of the summary indicate very likely and likely mean "the assessed likelihood, using expert judgment", are over 90% and 66% respectively.
The report notes many observed changes in the Earth's climate including atmospheric composition, global average temperatures, ocean conditions, and other climate changes.
Cold days, cold nights, and frost events have become less frequent. Hot days, hot nights, and heat waves have become more frequent. Additionally:
The SPM documents increases in wind intensity, decline of permafrost coverage, and increases of both drought and heavy precipitation events. Additionally:
Table SPM-2 lists recent trends along with certainty levels for the trend having actually occurred, for a human contribution to the trend, and for the trend occurring in the future. In relation to changes (including increased hurricane intensity) where the certainty of a human contribution is stated as "more likely than not" footnote f to table SPM-2 notes "Magnitude of anthropogenic contributions not assessed. Attribution for these phenomena based on expert judgment rather than formal attribution studies."
AR4 describes warming and cooling effects on the planet in terms of radiative forcing — the rate of change of energy in the system, measured as power per unit area (in SI units, W/m²). The report shows in detail the individual warming contributions (positive forcing) of carbon dioxide, methane, nitrous oxide, halocarbons, other human warming factors, and the warming effects of changes in solar activity. Also shown are the cooling effects (negative forcing) of aerosols, land-use changes, and other human activities. All values are shown as a change from pre-industrial conditions.
Climate sensitivity is defined as the amount of global average surface warming following a doubling of carbon dioxide concentrations. It is likely to be in the range of 2 to 4.5 °C, with a best estimate of about 3 °C. This range of values is not a projection of the temperature rise we will see in the 21st century, since the future change in carbon dioxide concentrations is unknown, and factors besides carbon dioxide concentrations affect temperature.
Model projections are made based on an analysis of various computer climate models running within different SRES scenarios. As a result, predictions for the 21st century are as shown below.
Scenario-specific projections are based on analysis of multiple runs by multiple climate models, using the various SRES Scenarios. "Low scenario" refers to B1, the most optimistic scenario family. "High scenario" refers to A1FI, the most pessimistic scenario family.
In the weeks before publication of the first report, controversy broke out about the report's projections of sea-level change, which in the new report was estimated at less than previous estimates. The now-published text gives a warning that the new estimation of sea-level could be too low: "Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise." The mid-points of the sea level rise estimates are within ±10% of those from the TAR; but the range has narrowed.
Lord Rees, the president of the Royal Society, said, "This report makes it clear, more convincingly than ever before, that human actions are writ large on the changes we are seeing, and will see, to our climate. The IPCC strongly emphasises that substantial climate change is inevitable, and we will have to adapt to this. This should compel all of us - world leaders, businesses and individuals - towards action rather than the paralysis of fear. We need both to reduce our emissions of greenhouse gases and to prepare for the impacts of climate change. Those who would claim otherwise can no longer use science as a basis for their argument.
U.S. Energy Secretary Samuel Bodman told a news conference that the report was "sound science" and "As the president has said, and this report makes clear, human activity is contributing to changes in our earth's climate and that issue is no longer up for debate. Kurt Volker, Principal Deputy Assistant Secretary for European and Eurasian Affairs, said, "We support the recent IPCC report, in which U.S. scientists played a leading role.
Based on the report, 46 countries in a "Paris Call for Action" read out by French President Chirac, have called for the creation of a United Nations Environment Organization (UNEO), which is to have more power than the current United Nations Environment Programme (UNEP), and is to be modelled after the more powerful World Health Organization. The 46 countries included the European Union nations, but notably did not include the United States, China, Russia, and India, the top four emitters of greenhouse gases.
WGII states that "evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases."
With a High Confidence (about an 8 in 10 chance to be correct) WGII asserts that climate change has resulted in:
With a Very High Confidence (about a 9 in 10 chance to be correct) WGII asserts that climate change is affecting terrestrial biological systems in that:
WGII also states that the ocean has become more acidic because it has absorbed human-caused carbon dioxide. Ocean pH has dropped by 0.1, but how this affects marine life is not documented.
U.S. negotiators managed to eliminate language calling for cuts in greenhouse gas emissions, according to Patricia Romero Lankao, a lead author from the National Center for Atmospheric Research (NCAR). The original draft read: "However, adaptation alone is not expected to cope with all the projected effects of climate change, and especially not over the long run as most impacts increase in magnitude. Mitigation measures will therefore also be required." The second sentence does not appear in the final version of the report.
China objected to wording that said "based on observed evidence, there is very high confidence that many natural systems, on all continents and in most oceans, are being affected by regional climate changes, particularly temperature increases." When China asked that the word "very" be stricken, three scientific authors balked, and the deadlock was broken only by a compromise to delete any reference to confidence levels.
The IPCC convened in Bangkok on April 30 to start discussions on the draft Summary, with the participation of over 400 scientists and experts from about 120 countries. At the full IPCC meeting on May 4, agreement was reached by the larger gathering of some 2,000 delegates. One of the key debates concerned a proposal to limit concentrations of greenhouse gases in the atmosphere to between 445 parts per million and 650 parts per million to avoid dangerous climate change, with pressure from developing countries to raise the lower limit. Despite this, the figures from the original proposal were incorporated into the Summary for Policymakers. The Summary concludes that stabilization of greenhouse gas concentrations is possible at a reasonable cost, with stabilization between 445ppm and 535ppm costing less than 3% of global GDP.
The WG III report analyses mitigation options for the main sectors in the near-term, addressing also cross-sectorial matters such as synergies, co-benefits, and trade-offs. It also provides information on long-term mitigation strategies for various stabilization levels, paying special attention to implications of different short-term strategies for achieving long-term goals.
|Sector||Key mitigation technologies and practices currently commercially available||Key mitigation technologies and practices projected to be commercialized before 2030|
|Energy Supply||Improved supply and distribution efficiency; fuel switching from coal to gas; nuclear power; renewable heat and power (hydropower, solar, wind, geothermal and bioenergy); combined heat and power; early applications of CCS (e.g. storage of removed CO2 from natural gas)||Carbon Capture and Storage (CCS) for gas, biomass and coal-fired electricity generating facilities; advanced nuclear power; advanced renewable energy, including tidal and waves energy, concentrating solar, and solar PV.|
|Transport||More fuel efficient vehicles; hybrid vehicles; cleaner diesel vehicles; biofuels; modal shifts from road transport to rail and public transport systems; non-motorised transport (cycling, walking); land-use and transport planning||Second generation biofuels; higher efficiency aircraft; advanced electric and hybrid vehicles with more powerful and reliable batteries|
|Buildings||Efficient lighting and daylighting; more efficient electrical appliances and heating and cooling devices; improved cook stoves, improved insulation; passive and active solar design for heating and cooling; alternative refrigeration fluids, recovery and recycle of fluorinated gases||Integrated design of commercial buildings including technologies, such as intelligent meters that provide feedback and control; solar PV integrated in buildings|
|Industry||More efficient end-use electrical equipment; heat and power recovery; material recycling and substitution; control of non-CO2 gas emissions; and a wide array of process-specific technologies||Advanced energy efficiency; CCS for cement, ammonia, and iron manufacture; inert electrodes for aluminium manufacture|
|Agriculture||Improved crop and grazing land management to increase soil carbon storage; restoration of cultivated peaty soils and degraded lands; improved rice cultivation techniques and livestock and manure management to reduce CH4 emissions; improved nitrogen fertilizer application techniques to reduce N2O emissions; dedicated energy crops to replace fossil fuel use; improved energy efficiency||Improvements of crop yields|
|Forestry/forests||Afforestation; reforestation; forest management; reduced deforestation; harvested wood product management; use of forestry products for bio-energy to replace fossil fuel use||Tree species improvement to increase biomass productivity and carbon sequestration. Improved remote sensing technologies for analysis of vegetation/ soil carbon sequestration potential and mapping land use change|
|Waste||Landfill methane recovery; waste incineration with energy recovery; composting of organic waste; controlled waste water treatment; recycling and waste minimization||Biocovers and biofilters to optimize CH4 oxidation|
The IPCC estimates that stabilizing atmospheric greenhouse gases at between 445-535ppm CO2 equivalent would result in a reduction of average annual GDP growth rates of less than 0.12%. stabilizing at 535 to 590ppm would reduce average annual GDP growth rates by 0.1%, while stabilization at 590 to 710ppm would reduce rates by 0.06%. There was high agreement and much evidence that a substantial fraction of these mitigation costs may be offset by benefits to health as a result of reduced air pollution, and that there would be further cost savings from other benefits such as increased energy security, increased agricultural production, and reduced pressure on natural ecosystems as well as, in certain countries, balance of trade improvements, provision of modern energy services to rural areas and employment.
The IPCC considered that achieving these reductions would require a 'large shift in the pattern of investment, although the net additional investment required ranges from negligible to 5-10%'.They also concluded that it is often more cost effective to invest in end-use energy efficiency improvement than in increasing energy supply.
In terms of electricity generation, the IPCC envisage that renewable energy can provide 30 to 35% of electricity by 2030 (up from 18% in 2005) at a carbon price of up to US$50/t, and that nuclear power can rise from 16% to 18%. They also warn that higher oil prices might lead to the exploitation of high-carbon alternatives such as oil sands, oil shales, heavy oils, and synthetic fuels from coal and gas, leading to increasing emissions, unless carbon capture and storage technologies are employed.
In the transport sector there was a medium level of agreement and evidence that the multiple mitigation options may be counteracted by increased use, and that there were many barriers and a lack of government policy frameworks.
There was high agreement and much evidence that, despite many barriers (particularly in the developing countries), new and existing buildings could reduce emissions considerably, and that this would also provide other benefits in terms of improved air quality, social welfare and energy security.
The IPCC reported that the effectiveness of mitigation efforts over the next two or three decades would have a large impact on the ability to stabilize atmospheric greenhouse gases at lower levels, and that the lower the ultimate stabilization levels, the more quickly emissions would need to peak and decline. For example, to stabilize at between 445 and 490ppm (resulting in an estimate global temperature 2 to 2.4oC above the pre-industrial average) emissions would need to peak before 2015, with 50 to 85% reductions on 2000 levels by 2050.
There was high agreement and much evidence that stabilization could be achieved by 2050 using currently available technologies, provided appropriate and effective incentives were put in place for their development, acquisition, deployment and diffusion, and that barriers were removed. For stabilization at lower levels the IPCC agreed that improvements of carbon intensity need to be made much faster than has been the case in the past, and that there would be a greater need for efficient public and private research, development & demonstration efforts and investment in new technologies during the next few decades. The IPCC points out that government funding in real absolute terms for most energy research programmes has been flat or declining for nearly 20 years, and is now about half the 1980 level. Delays in cutting emissions would lead to higher stabilization levels and increase the risk of more severe climate change impacts, as more of the current high-emission technologies would have been deployed.
Among the measures that might be used, there was high agreement and much evidence that policies that put a price on the cost of carbon emissions could provide incentives for consumers and producers. Carbon prices of 5 to 65 US$/tCO2 in 2030 and 15 to 130 US$/tCO2 by 2050 are envisaged for stabilization at around 550 ppm by 2100.
A draft version of the AR4 Synthesis Report, , "Subject to final copyedit", was published 16 November, 2007.
The six topics addressed in the Synthesis Report are:
The key findings from the AR4 Synthesis Report will be discussed Wednesday 13 December 2007 at the United Nations Climate Change Conference (UNFCCC COP 13--CMP 3) in Bali, Indonesia, which takes place 3-14 December (see UNFCCC home page).
model projections suggest significant extinctions (40-70% of species assessed) around the globe."
The Fourth Assessment Report has been the subject of criticism. Skeptics of anthropogenic global warming contend that their claims are not sufficiently incorporated in the report. Others regard the IPCC as too conservative in its estimates of potential harm from climate change.
Related to the subject of global warming in general, the IPCC Fourth Assessment Report has been discussed by various bodies such as government officials, special interest groups and scientific organizations; see the article "Politics of global warming" for a thorough discussion of the politics surrounding the phenomenon, and the positions of the various parties involved.