IPCC Fourth Assessment Report Totally Explained

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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.

Climate Change 2007: Report Overview

The Fourth Assessment Report (Climate Change 2007) is released in four distinct sections:

Working Group I Report (WGI): Climate Change 2007: The Physical Science Basis.
Working Group II Report (WGII): Climate Change 2007: Impacts, Adaptation and Vulnerability.
Working Group III Report (WGIII): Climate Change 2007: Mitigation of Climate Change (final version).
The Synthesis Report (SYR): (pre-copy edit version).

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.

Working Group I (WGI): The Physical Science Basis

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: is 1.8 °C with a likely range of 1.1 to 2.9 °C (3.2 °F with a likely range of 2.0 to 5.2 °F)

Best estimate for a "high scenario" is 4.0 °C with a likely range of 2.4 to 6.4 °C (7.2 °F with a likely range of 4.3 to 11.5 °F)

A temperature rise of about 0.1 °C per decade would be expected for the next two decades, even if greenhouse gas and aerosol concentrations were kept at year 2000 levels.

A temperature rise of about 0.2 °C per decade is projected for the next two decades for all SRES scenarios.

Confidence in these near-term projections is strengthened because of the agreement between past model projections and actual observed temperature increases.

Based on multiple models that all exclude ice sheet flow due to a lack of basis in published literature, it's estimated that sea level rise will be:

in a low scenario
   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 didn't include the United States, China, Russia, and India, the top four emitters of greenhouse gases.
Working Group II (WGII): Impacts, Adaptation and Vulnerability
The summary for policymakers for the Working Group II report was released on April 6, 2007. The full report was released September 18, 2007.
   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."
Observations
Some observed changes have been associated with climate change at varying levels of confidence.
   With a High Confidence (about an 8 in 10 chance to be correct) WGII asserts that climate change has resulted in:
More and larger glacial lakes.
Increasing ground instability in permafrost regions.
Increasing rock avalanches in mountain regions.
Changes in some Arctic and Antarctic ecosystems.
Increased run-off and earlier spring peak discharge in many glacier and snow-fed rivers.
Changes affecting algae, plankton, fish and zooplankton because rising water temperatures and changes in:
- ice cover
- salinity
- oxygen levels
- water circulation

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:

Spring events such as the unfolding of leaves, laying of eggs, and migration are happening earlier.

There are poleward and upward (to higher altitude) shifts in ranges of plant and animal species. 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 isn't documented.

Attribution of Changes

WGII acknowledges some of the difficulties of attributing specific changes to human-caused global warming, stating that "Limitations and gaps prevent more complete attribution of the causes of observed system responses to anthropogenic warming." but found that the agreement between observed and projected changes was "Nevertheless ... sufficient to conclude with high confidence that anthropogenic warming over the last three decades has had a discernible influence on many physical and biological systems."

Projections

WGII describes some of what might be expected in the coming century, based on studies and model projections.

Fresh Water

It is projected with High Confidence that:

Dry regions are projected to get drier, and wet regions are projected to get wetter: "By mid-century, annual average river runoff and water availability are projected to increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics..."

Drought-affected areas will become larger.

Heavy precipitation events are very likely to become more common and will increase flood risk.

Water supplies stored in glaciers and snow cover will be reduced over the course of the century.

Ecosystems

It is projected with High Confidence that:

The resilience of many ecosystems is likely to be exceeded this century by a combination of climate change and other stressors.

Carbon removal by terrestrial ecosystems is likely to peak before mid-century and then weaken or reverse. This would amplify climate change.

Food

It is projected with Medium Confidence (about 5 in 10 chance to be correct) that globally, potential food production will increase for temperature rises of 1-3 °C, but decrease for higher temperature ranges. Fortunately, temperatures are not expected to rise to these ranges in the near future.

Coastal Systems

It is projected with Very High Confidence that:

Coasts will be exposed to increasing risks such as coastal erosion due to climate change and sea-level rise.

"Increases in sea-surface temperature of about 1-3 °C are projected to result in more frequent coral bleaching events and widespread mortality unless there's thermal adaptation or acclimatisation by corals."

"Many millions more people are projected to be flooded every year due to sea-level rise by the 2080s."

Objections to original WGII language

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 isn't 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 doesn't appear in the final version of the report.
   China objected to wording that said "based on observed evidence, there's 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. Summary for Policymakers (SPM) was published on 4 May, 2007 at the 26th session of the IPCC. The full WG III report was published online in September, 2007.
   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.

Mitigation in the short and medium term (until 2030)

The Summary for Policymakers concludes that there was a high level of agreement and much evidence that 'there is substantial economic potential for the mitigation of global greenhouse gas emissions over the coming decades, that could offset the projected growth of global emissions or reduce emissions below current levels', taking into account financial and social costs and benefits. The technologies with the largest economic potential within this timescale are considered to be:
Key mitigation technologies and practices by sector>

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 (for example 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's 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.

Mitigation in the long term (after 2030)

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 2.4^oC 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.

AR4 Synthesis Report

A draft version of the AR4 Synthesis Report,, "Subject to final copyedit", was published 16 November, 2007.

The Synthesis Report goes one step further [thanthe first three Climate Change 2007 Working Group Reports]: it's the decisive effort to integrate and compact this wealth of information into a readable and concise document explicitly targeted to the policymakers.
The Synthesis Report also brings in relevant parts some material [sic] contained in the full Working Group Reports over and above what is included in the Summary for Policymakers in these three Reports. It is designed to be a powerful, scientifically authoritative document of high policy relevance, which will be a major contribution to the discussions at the 13th Conference of the Parties in Bali during December 2007. In fact, this Conference was postponed to December to allow the IPCC Synthesis Report to come out first.

The six topics addressed in the Synthesis Report are:

Observed changes in climate and its effects (Working Groups 1-2).

Causes of change (WGs 1, 3).

Climate change and its impacts in the near and long term under different scenarios (WGs 1-3).

Adaptation and mitigation options and responses, and the inter-relationship with sustainable development, at global and regional levels (WGs 2-3).

The long term perspective: scientific and socio-economic aspects relevant to adaptation and mitigation, consistent with the objectives and provisions of the Convention [sic], and in the context of sustainable development (WGs 1-3).

Robust findings, key uncertainties (WGs 1-3). The "Convention" mentioned in Topic 5 is the UN Framework Convention on Climate Change (UNFCCC).
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).

Anthropogenic warming could lead to some impacts that are abrupt or irreversible

The SPM states that "Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change."

"There is medium confidence that approximately 20-30% of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5-2.5°C (relative to 1980-1999). As global average temperature increase exceeds about 3.5°C, model projections suggest significant extinctions (40-70% of species assessed) around the globe."

"Partial loss of ice sheets on polar land could imply metres of sea level rise, major changes in coastlines and inundation of low-lying areas, with greatest effects in river deltas and low-lying islands. Such changes are projected to occur over millennial time scales, but more rapid sea level rise on century time scales can't be excluded."

Criticism

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.

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