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The Intergovernmental Panel on Climate Change (IPCC) is a scientific intergovernmental body tasked to evaluate the risk of climate change caused by human activity. The panel was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), two organizations of the United Nations. The IPCC shared the 2007 Nobel Peace Prize with former Vice President of the United States Al Gore.

The IPCC does not carry out its own original research, nor does it do the work of monitoring climate or related phenomena itself. A main activity of the IPCC is publishing special reports on topics relevant to the implementation of the UN Framework Convention on Climate Change (UNFCCC), an international treaty that acknowledges the possibility of harmful climate change; implementation of the UNFCCC led eventually to the Kyoto Protocol. The IPCC bases its assessment mainly on peer reviewed and published scientific literature. The IPCC is only open to member states of the WMO and UNEP.IPCC reports are widely cited in almost any debate related to climate change. National and international responses to climate change generally regard the UN climate panel as authoritative.

The summary reports (i.e. Summary for Policymakers), which draw the most media attention, include review by participating governments in addition to scientific review.


The principles of the IPCC operation are assigned by the relevant WMO Executive Council and UNEP Governing Council resolutions and decisions as well as on actions in support of the UN Framework Convention on Climate Change process.

The stated aims of the IPCC are to assess scientific information relevant to:
  1. human-induced climate change,
  2. the impacts of human-induced climate change,
  3. options for adaptation and mitigation.

The history of the IPCC is described in a .

IPCC Assessment Reports

The IPCC published its first assessment report in 1990, a supplementary report in 1992, a second assessment report in 1995, and a third assessment report in 2001. A fourth assessment report was released in 2007. Each assessment report is in three volumes, corresponding to Working Groups I, II and III. Unqualified, "the IPCC report" is often used to mean the Working Group I report, which covers the basic science of climate change.

IPCC First Assessment Report: 1990

The IPCC first assessment report was completed in 1990, and served as the basis of the United Nations Framework Convention on Climate Change (UNFCCC).

The executive summary of the WG I Summary for Policymakers report says they are certain that emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases, resulting on average in an additional warming of the Earth's surface. They calculate with confidence that CO2 has been responsible for over half the enhanced greenhouse effect. They predict that under BAU increase of global mean temperature during the [21st] century of about 0.3 oC per decade. They judge that global mean surface air temperature has increased by 0.3 to 0.6 oC over the last 100 years, broadly consistent with prediction of climate models, but also of the same magnitude as natural climate variability. The unequivocal detection of the enhanced greenhouse effect is not likely for a decade or more.

IPCC Supplementary Report: 1992

The 1992 supplementary report was an update, requested in the context of the negotiations on the Framework Convention on Climate Change at the Earth Summit (United Nations Conference on Environment and Development) in Rio de Janeiromarker in 1992.

The major conclusion was that research since 1990 did "not affect our fundamental understanding of the science of the greenhouse effect and either confirm or do not justify alteration of the major conclusions of the first IPCC scientific assessment". It noted that transient (time-dependent) simulations, which had been very preliminary in the FAR, were now improved, but did not include aerosol or ozone changes.

IPCC Second Assessment Report: Climate Change 1995

Climate Change 1995, the IPCC Second Assessment Report (SAR), was finished in 1996. It is split into four parts:
  • A synthesis to help interpret UNFCCC article 2.
  • The Science of Climate Change (WG I)
  • Impacts, Adaptations and Mitigation of Climate Change (WG II)
  • Economic and Social Dimensions of Climate Change (WG III)

Each of the last three parts was completed by a separate working group, and each has a Summary for Policymakers (SPM) that represents a consensus of national representatives. The SPM of the WG I report contains headings:

  1. Greenhouse gas concentrations have continued to increase
  2. Anthropogenic aerosols tend to produce negative radiative forcings
  3. Climate has changed over the past century (air temperature has increased by between 0.3 and 0.6 °C since the late 19th century; this estimate has not significantly changed since the 1990 report).
  4. The balance of evidence suggests a discernible human influence on global climate (considerable progress since the 1990 report in distinguishing between natural and anthropogenic influences on climate, because of: including aerosols; coupled models; pattern-based studies)
  5. Climate is expected to continue to change in the future (increasing realism of simulations increases confidence; important uncertainties remain but are taken into account in the range of model projections)
  6. There are still many uncertainties (estimates of future emissions and biogeochemical cycling; models; instrument data for model testing, assessment of variability, and detection studies)


A December 20, 1995, Reuters report quoted British scientist Keith Shine, one of IPCC's lead authors, discussing the Policymakers' Summary. He said: "We produce a draft, and then the policymakers go through it line by line and change the way it is presented.... It's peculiar that they have the final say in what goes into a scientists' report". It is not clear, in this case, whether Shine was complaining that the report had been changed to be more skeptical, or less, or something else entirely.

Solid-state physicist Frederick Seitz, president emeritus of Rockefeller University, past president of the National Academy of Sciences, and former health consultant for R. J. Reynolds Tobacco Company publicly denounced the IPCC report, writing "I have never witnessed a more disturbing corruption of the peer-review process than the events that led to this IPCC report". He opposed it in the Leipzig Declaration of S. Fred Singer's Science and Environmental Policy Project.

In turn, Seitz's comments were vigorously opposed by the presidents of the American Meteorological Society and University Corporation for Atmospheric Research, who wrote about a "systematic effort by some individuals to undermine and discredit the scientific process that has led many scientists working on understanding climate to conclude that there is a very real possibility that humans are modifying Earth's climate on a global scale. Rather than carrying out a legitimate scientific debate... they are waging in the public media a vocal campaign against scientific results with which they disagree".

S. Fred Singer disseminated a letter about Chapter 8 of the IPCC Working Group I report, asserting that:
  1. Chapter 8 was altered substantially to make it conform to the Summary;
  2. Three key clauses — expressing the consensus of authors, contributors, and reviewers — should have been placed into the Summary instead of being deleted from the approved draft chapter;

Benjamin D. Santer, Convening Lead Author of Chapter 8 of 1995 IPCC Working Group I Report, replied:
  1. All revisions were made with the sole purpose of producing the best-possible and most clearly explained assessment of the science, and were under the full scientific control of the Convening Lead Author of Chapter 8.
  2. None of the changes were politically motivated.

Santer's position was supported by fellow IPCC authors and senior figures of the American Meteorological Society and University Corporation for Atmospheric Research. In 1997, Paul Edwards and IPCC author Stephen Schneider published a paper rebutting criticisms of the IPCC report.

Debate over value of a statistical life

The Second Assessment Report was controversial in its treatment of the economic value of human life. In environmental economics, it is customary to value the health impacts of climate change on the basis of willingness to pay for risk reduction. An advantage of this method is that health risks of climate change are treated like any other health risk. Some have commented on the difficultly of calculating the costs of climate change impacts such as human mortality. For example, in calculations based on risk reduction, the value of a statistical life is assessed to be much higher in rich countries than in poor countries.

This information was presented in the full Second Assessment Report, however, dispute arose over the Report's Summary for Policymakers. The Summary for Policymakers (SPM) is prepared with the input of government delegates and IPCC experts. Governments were unhappy with the cost-benefit valuation of human life, and this was implied in the SPM. David Pearce, the IPCC convening lead author who oversaw the relevant chapter of the Report, officially dissented on this summary, commenting that:
The relevant chapter [of the Report] values of statistical life based on actual studies in different countries.
Whether the values used remain as in Chapter 6 or whether a common global average is used makes no difference to the results.
What the authors of Chapter 6 did not accept, and still do not accept, was the call from a few [government] delegates for a common valuation based on the highest number for willingness to pay.

Michael Grubb, a lead author for several IPCC reports, later commented:
Many of us think that the governments were basically right.
The metric [used by Pearce] makes sense for determining how a given government might make tradeoffs between its own internal projects.
But the same logic fails when the issue is one of damage inflicted by some countries on others: why should the deaths inflicted by the big emitters — principally the industrialised countries — be valued differently according to the wealth of the victims' countries?

IPCC Third Assessment Report: Climate Change 2001

The Third Assessment Report (TAR) consists of four reports, three of them from its working groups:
  • Working Group I: The Scientific Basis
  • Working Group II: Impacts, Adaptation and Vulnerability
  • Working Group III: Mitigation
  • Synthesis Report

The "headlines" from the Summary for Policymakers in The Scientific Basis were:

  1. An increasing body of observations gives a collective picture of a warming world and other changes in the climate system (The global average surface temperature has increased over the 20th century by about 0.6 °C; Temperatures have risen during the past four decades in the lowest 8 kilometers of the atmosphere; Snow cover and ice extent have decreased)
  2. Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that are expected to affect the climate (Anthropogenic aerosols are short-lived and mostly produce negative radiative forcing; Natural factors have made small contributions to radiative forcing over the past century)
  3. Confidence in the ability of models to project future climate has increased (Complex physically based climate models are required to provide detailed estimates of feedback and of regional features. Such models cannot yet simulate all aspects of climate (e.g., they still cannot account fully for the observed trend in the surface-troposphere temperature difference since 1979) and there are particular uncertainties associated with clouds and their interaction with radiation and aerosols. Nevertheless, confidence in the ability of these models to provide useful projections of future climate has improved due to their demonstrated performance on a range of space and time-scales.)
  4. There is new and stronger evidence that most of the warming observed over the past 50 years is attributable to human activities
  5. Human influences will continue to change atmospheric composition throughout the 21st century
  6. Global average temperature and sea level are projected to rise under all IPCC SRES scenarios

The TAR estimate for the climate sensitivity is 1.5 to 4.5 °C; and the average surface temperature is projected to increase by 1.4 to 5.8 Celsius degrees over the period 1990 to 2100, and the sea level is projected to rise by 0.1 to 0.9 meters over the same period. The wide range in predictions is based on scenarios that assume different levels of future CO2 emissions. Each scenario then has a range of possible outcomes associated with it. The most optimistic outcome assumes an aggressive campaign to reduce CO2 emissions; the most pessimistic is a "business as usual" scenario. Other scenarios fall in between.

IPCC uses the best available predictions and their reports are under strong scientific scrutiny.The IPCC concedes that there is a need for better models and better scientific understanding of some climate phenomena, as well as the uncertainties involved.Critics assert that the data is insufficient to determine the real importance of greenhouse gases in climate change.Sensitivity of climate to greenhouse gases may be overestimated or underestimated because of flaws in the models and because the importance of some external factors may be misestimated. The predictions are based on scenarios, and the IPCC did not assign any probability to the 35 scenarios used.

Economic growth estimates debate

Castles and Henderson asserted that the IPCC's use of market exchange rates in the Special Report on Emissions Scenarios to convert GDP measures into a common currency is inappropriate, and that, for most countries a Purchasing Power Parity conversion would yield higher estimates of income. It follows that the rate of growth implied by an assumption of income convergence is higher if exchange rate conversions are used. They imply that this is likely to produce biased projections of emissions. Nebojsa Nakicenovic et al. claim that this is incorrect because, provided an internally consistent procedure is used, projections of emissions are unaffected by the choice of index number used to measure GDP. See the discussion under Special Report on Emissions Scenarios.

Physical modeling debate

MITmarker professor Richard Lindzen, one of the lead authors of the IPCC Working Group I Report, has criticised the IPCC Summary for Policymakers document before the U.S. Senate Committee on Commerce, Science and Transportation:

Sir John Houghton, former Chair of the IPCC Working Group I Report, has commented on Lindzen's criticisms of the IPCC:

[...] Professor Lindzen [has expressed] his satisfaction with the [IPCC] report’s chapters as good scientific documents.
He has often, however, gone on to express his view that the conclusions of the Policymakers Summary did not faithfully represent the chapters.
But he has never provided any supporting evidence for that statement [...]

It is important to note that IPCC Policymakers’ Summaries are agreed unanimously at intergovernmental meetings involving over 200 government delegates from around 100 countries.
This agreement is only achieved after several days of scientific debate (only scientific arguments not political ones are allowed) the main purpose of which is to challenge the scientific chapter authors regarding the accuracy, clarity and relevance of the summary and most especially its consistency with the underlying chapters.
Agreement at such a meeting has ensured that the resulting document, so far as is possible, is scientifically accurate, balanced and free from personal or political bias.

IPCC Fourth Assessment Report: Climate Change 2007

The four SRES scenario families of the Fourth Assessment Report vs. associated changes in global-mean temperature until 2100
more economic focus more environmental focus

(homogeneous world)

rapid economic growth

(groups: A1T/A1B/A1Fl)

1.4 - 6.4 °C

global environmental sustainability 

1.1 - 2.9 °C

(heterogeneous world)

regionally oriented

economic development

2.0 - 5.4 °C

local environmental sustainability

1.4 - 3.8 °C

The Fourth Assessment Report (AR4) was completed in early 2007. Like previous assessment reports, it consists of four reports, three of them from its working groups.

Working Group I dealt with the "Physical Science Basis of Climate Change."The Working Group I Summary for Policymakers (SPM) was published on February 2, 2007 and revised on February 5, 2007. There was also a February 2, 2007 press release. The full WGI report was published in March. The key conclusions of the SPM were that:

  • Warming of the climate system is unequivocal.
  • Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (human) greenhouse gas concentrations.
  • Anthropogenic warming and sea level rise would continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized, although the likely amount of temperature and sea level rise varies greatly depending on the fossil intensity of human activity during the next century (pages 13 and 18).
  • The probability that this is caused by natural climatic processes alone is less than 5%.
  • World temperatures could rise by between 1.1 and 6.4 °C (2.0 and 11.5 °F) during the 21st century (table 3) and that:
    • Sea levels will probably rise by 18 to 59 cm (7.08 to 23.22 in) [table 3].
    • There is a confidence level >90% that there will be more frequent warm spells, heat waves and heavy rainfall.
    • There is a confidence level >66% that there will be an increase in droughts, tropical cyclones and extreme high tides.
  • Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium.
  • Global atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values over the past 650,000 years

In IPCC statements "most" means greater than 50%, "likely" means at least a 66% likelihood, and "very likely" means at least a 90% likelihood.

An outline of chapters in the WGI report (as of November 3, 2005) and a list of the report's authors (as of March 10, 2005) were made available before publication of the SPM.

The Summary for Policymakers for the Working Group II report was released on April 6, 2007.The Summary for Policymakers for the Working Group III report was released on May 4, 2007.The AR4 Synthesis Report (SYR) was released on November 17, 2007.

IPCC Fifth Assessment Report: Climate Change 2014

The IPCC is currently starting to outline its Fifth Assessment Report (AR5) which will be finalized in 2014. As it has been the case in the past, the outline of the AR5 will be developed through a scoping process which involves climate change experts from all relevant disciplines and users of IPCC reports, in particular representatives from governments. As a first step, experts, governments and organizations involved in the Fourth Assessment Report have been asked to submit comments and observations in writing. These submissions are currently being analysed by members of the Bureau. The scoping meeting of experts to define the outline of the AR5 is scheduled for 13-17 July 2009. The outline will be submitted to the 31st Session of the IPCC to be held in Bali, Indonesia, 26-29 October 2009.

IPCC Methodology Reports

Within IPCC the National Greenhouse Gas Inventory Program (IPCC-NGGIP) develops methods and methodologies to estimate emissions of greenhouse gases. IPCC-NGGIP has been undertaken since 1991 by the IPCC WG I in close collaboration with the Organisation for Economic Co-operation and Development (OECD) and the International Energy Agency (IEA).The objectives of the IPCC-NGGIP are:
  • to develop and refine an internationally-agreed methodology and software for the calculation and reporting of national GHG emissions and removals; and
  • to encourage the widespread use of this methodology by countries participating in the IPCC and by signatories of the United Nations Framework Convention on Climate Change (UNFCCC).

Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories

The Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (1996 GLs) provide the methodological basis for the estimation of national greenhouse gas emission inventory. Over time these 1996GLs have been completed with guidance on so-called "Good Practice": Together the 1996 GLs and both good practice reports are to be used by parties to the UNFCCC and to the Kyoto Protocol in their annual submissions of national greenhouse gas inventories

2006 IPCC Guidelines for National Greenhouse Gas Inventories

The 2006 IPCC Guidelines for National Greenhouse Gas Inventories ( IPCC 2006 GLs) comprises the latest versions of these emission estimation methodologies, including a large number of default emission factors. Although the IPCC has prepared these new version of the guidelines on request of the partires to the UNFCCC, the methods have not been officially accepted yet for use in national greenhouse gas emisiosns reporting under the UNFCCC and the Kyoto Protocol.


The Chair of the IPCC is Rajendra K. Pachauri, elected in May 2002; previously Robert Watson headed the IPCC. The chair is assisted by an elected Bureau including vice-chairs, Working Group co-chairs and a Secretariat (see below).

The IPCC Panel is composed of representatives appointed by governments and organizations. Participation of delegates with appropriate expertise is encouraged. Plenary sessions of the IPCC and IPCC Working Groups are held at the level of government representatives. Non Governmental and Intergovernmental Organizations may be allowed to attend as observers. Sessions of the IPCC Bureau, workshops, expert and lead authors meetings are by invitation only. Attendance at the 2003 meeting included 350 government officials and climate change experts. After the opening ceremonies, closed plenary sessions were held. The meeting report states there were 322 persons in attendance at Sessions with about seven-eighths of participants being from governmental organizations.

The IPCC has published four comprehensive assessment reports reviewing the latest climate science, as well as a number of special reports on particular topics. These reports are prepared by teams of relevant researchers selected by the Bureau from government nominations. Drafts of these reports are made available for comment in open review processes to which anyone may contribute.

The IPCC does not carry out research nor does it monitor climate related data. The responsibility of the lead authors of IPCC reports is to assess available information about climate change drawn mainly from the peer reviewed and published scientific/technical literature.

There are several major groups:
  • IPCC Panel: Meets in plenary session about once a year and controls the organization's structure, procedures, and work programme. The Panel is the IPCC corporate entity.
  • Chair: Elected by the Panel.
  • Secretariat: Oversees and manages all activities. Supported by UNEP and WMO.
  • Bureau: Elected by the Panel. Chaired by the Chair. 30 members include IPCC Vice-Chairs, Co-Chairs and Vice-Chairs of Working Groups and Task Force.
  • Working Groups: Each has two Co-Chairs, one from the developed and one from developing world, and a technical support unit.
    • Working Group I: Assesses scientific aspects of the climate system and climate change.
    • Working Group II: Assesses vulnerability of socio-economic and natural systems to climate change, consequences, and adaptation options.
    • Working Group III: Assesses options for limiting greenhouse gas emissions and otherwise mitigating climate change.
  • Task Force on National Greenhouse Gas Inventories

The IPCC receives funding from UNEP, WMO, and its own Trust Fund for which it solicits contributions from governments.


People from over 130 countries contributed to the IPCC Fourth Assessment Report over the previous 6 years. These people included more than 2500 scientific expert reviewers, more than 800 contributing authors, and more than 450 lead authors.

Of these, the Working Group 1 report (including the summary for policy makers) included contributions by 600 authors from 40 countries, over 620 expert reviewers, a large number of government reviewers, and representatives from 113 governments.


The IPCC concentrates its activities on the tasks allotted to it by the relevant WMO Executive Council and UNEP Governing Council resolutions and decisions as well as on actions in support of the UN Framework Convention on Climate Change process.

In April 2006, the IPCC released the IPCC Fourth Assessment Report or AR4. Reports of the workshops held so far are available at the IPCC website.
  • Working Group I:
    • Report was due to be finalized during February 2007 and was finished on schedule.
    • By May 2005, there had been 3 AR4 meetings, with only public information being meeting locations, an author list, one invitation, one agenda, and one list of presentation titles.
    • By December 2006, governments were reviewing the revised summary for policy makers.
  • Working Group II:
    • Report was due to be finalized in mid-2007 and was completed on schedule.
    • In May 2005, there had been 2 AR4 meetings, with no public information released.
    • One shared meeting with WG III had taken place, with a published summary.
  • Working Group III:
    • Report was due to be finalized in mid-2007.
    • In May 2005, there had been 1 AR4 meeting, with no public information released.

The AR4 Synthesis Report (SYR) was finalized in November 2007. Documentation on the scoping meetings for the AR4 are available as are the outlines for the WG I report and a provisional author list .

While the preparation of the assessment reports is a major IPCC function, it also supports other activities, such as the Data Distribution Centre and the National Greenhouse Gas Inventories Programme, required under the UNFCCC. This involves publishing default emission factors, which are factors used to derive emissions estimates based on the levels of fuel consumption, industrial production and so on.

The IPCC also often answers inquiries from the UNFCCC Subsidiary Body for Scientific and Technological Advice (SBSTA).


Scope and preparation of the reports

The IPCC reports are a compendium of peer reviewed and published science. Each subsequent IPCC report notes areas where the science has improved since the previous report and also notes areas where further research is required.

There are generally three stages in the review process :
  • Expert review (6–8 weeks)
  • Government/expert review
  • Government review of:
    • Summaries for Policymakers
    • Overview Chapters
    • Synthesis Report
Review comments are in an open archive for at least five years.

There are several types of endorsement which documents receive :
  • approval: Material has been subjected to detailed, line by line discussion and agreement.
    • Working Group Summaries for Policymakers are approved by their Working Groups.
    • Synthesis Report Summary for Policymakers is approved by Panel.
  • adoption: Endorsed section by section (and not line by line).
    • Panel adopts Overview Chapters of Methodology Reports.
    • Panel adopts IPCC Synthesis Report.
  • acceptance: Not been subject to line by line discussion and agreement, but presents a comprehensive, objective, and balanced view of the subject matter.
    • Working Groups accept their reports.
    • Task Force Reports are accepted by the Panel.
    • Working Group Summaries for Policymakers are accepted by the Panel after group approval.

The Panel is responsible for the IPCC and its endorsement of Reports allows it to ensure they meet IPCC standards. The Panel's approval process has been criticized for changing the product of the experts who create the Reports. On the other hand, not requiring Panel re-endorsement of Reports has also been criticized, after changes required by the approval process were made to Reports.


Each chapter has a number of authors who are responsible for writing and editing the material. A chapter typically has two Coordinating Lead Authors, ten to fifteen Lead Authors, and a somewhat larger number of Contributing Authors. The Coordinating Lead Authors are responsible for assembling the contributions of the other authors, ensuring that they meet stylistic and formatting requirements, and reporting to the Working Group chairs. Lead Authors are responsible for writing sections of chapters. Contributing Authors prepare text, graphs or data for inclusion by the Lead Authors.

Authors for the IPCC reports are chosen from a list of researchers prepared by governments, and participating organisations and the Working Group/Task Force Bureaux, and other experts as appropriate, known through their publications and works ( , 4.2.1,2). The composition of the group of Coordinating Lead Authors and Lead Authors for a section or chapter of a Report is intended to reflect the need to aim for a range of views, expertise and geographical representation (ensuring appropriate representation of experts from developing and developed countries and countries with economies in transition).

Nobel Peace Prize

In December 2007, the IPCC was awarded the Nobel Peace Prize "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change." The award is shared with Former U.S. Vice-President Al Gore for his work on climate change and the documentary An Inconvenient Truth.

Criticism of IPCC

Christopher Landsea resignation

In January 2005 Christopher Landsea resigned from work on the IPCC AR4, saying that he viewed the process "as both being motivated by pre-conceived agendas and being scientifically unsound" because of Kevin Trenberth's public contention that global warming was contributing to recent hurricane activity. Roger A. Pielke, Jr. who published Landsea's letter writes: "How anyone can deny that political factors were everpresent in the negotiations isn't paying attention [sic]", but notes that the actual report "Despite the pressures, on tropical cyclones they figured out a way to maintain consistency with the actual balance of opinion(s) in the community of relevant experts." He continues "So there might be a human contribution (and presumably this is just to the observed upwards trends observed in some basins, and not to downward trends observed in others, but this is unclear) but the human contribution itself has not been quantitatively assessed, yet the experts, using their judgment, expect it to be there. In plain English this is what is called a 'hypothesis' and not a 'conclusion.' And it is a fair representation of the issue."

Emphasis of the "hockey stick" graph

The third assessment report prominently featured a graph labeled "Millennial Northern Hemisphere temperature reconstruction" from a paper by Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes (MBH98) often referred to as the "Hockey Stick Graph". This graph differed from a schematic in the first assessment report which depicted larger global temperature variations over the past 1000 years, and higher temperatures during the Medieval Warm Period than the present day. (The schematic was not an actual plot of data.) The appearance of MBH98 in the TAR was widely construed as demonstrating that the current warming period is exceptional in comparison to temperatures between 1000 and 1900. The methodology used to produce this graph was criticized in an article by Stephen McIntyre and Ross McKitrick. In a 2006 letter to Nature, Bradley, Hughes and Mann pointed out that their original article had said that "more widespread high-resolution data are needed before more confident conclusions can be reached" and that the uncertainties were "the point of the article."

Conservative nature of IPCC reports

Some critics have contended that the IPCC reports tend to underestimate dangers, understate risks, and report only the "lowest common denominator" findings.

On February 1, 2007, the eve of the publication of IPCC's major report on climate, a study was published suggesting that temperatures and sea levels have been rising at or above the maximum rates proposed during the last IPCC report in 2001. The study compared IPCC 2001 projections on temperature and sea level change with observations. Over the six years studied, the actual temperature rise was near the top end of the range given by IPCC's 2001 projection, and the actual sea level rise was above the top of the range of the IPCC projection.

An example of scientific research which has indicated that previous estimates by the IPCC, far from overstating dangers and risks, has actually understated them (this may be due, in part, to the expanding human understanding of climate) is a study on projected rises in sea levels. When the researchers' analysis was "applied to the possible scenarios outlined by the Intergovernmental Panel on Climate Change (IPCC), the researchers found that in 2100 sea levels would be 0.5–1.4 m above 1990 levels. These values are much greater than the 9–88 cm as projected by the IPCC itself in its Third Assessment Report, published in 2001.

In reporting criticism by some scientists that IPCC's then-impending January 2007 report understates certain risks, particularly sea level rises, an AP story quoted Stefan Ramstorf, professor of physics and oceanography at Potsdam University as saying:

In his December 2006 book, Hell and High Water: Global Warming, and in an interview on Fox News on January 31, 2007, energy expert Joseph Romm noted that the IPCC Fourth Assessment Report is already out of date and omits recent observations and factors contributing to global warming, such as the release of greenhouse gases from thawing tundra.

Political influence on the IPCC has been documented by the release of a memo by ExxonMobil to the Bush administration, and its effects on the IPCC's leadership. The memo led to strong Bush administration lobbying, evidently at the behest of ExxonMobil, to oust Robert Watson, a climate scientist, from the IPCC chairmanship, and to have him replaced by Pachauri, who was seen at the time as more mild-mannered and industry-friendly.

IPCC processes

In 2005, the UK House of Lordsmarker Select Committee on Economic Affairs produced a report on the economics of climate change. It commented on the IPCC process:

Interestingly, the Stern Review ordered by the UK government, whose findings were released in October 2006, made a stronger argument in favor of urgent action to combat human-made climate change than previous analyses, including some by IPCC. The conclusions of the Stern Review have been contested, however.

The structural elements of the IPCC processes have been criticized in other ways, with the design of the processes during the formation of the IPCC making its reports prone not to exaggerations, but tounderestimating dangers, under-stating risks, and reporting only the"least common denominator" findings which by design make it throughthe bureaucracy. As noted by Spencer Weart, Director of the Center for History of Physics at the American Institute of Physics,

Outdatedness of reports

Since the IPCC does not carry out its own research, it operates on the basis of scientific papers and independently documented results from other scientific bodies, and its schedule for producing reports requires a deadline for submissions prior to the report's final release. In principle, this means that any significant new evidence or events that change our understanding of climate science between this deadline and publication of an IPCC report cannot be included. In an area of science where our scientific understanding is rapidly changing, this has been raised as a serious shortcoming in a body which is widely regarded as the ultimate authority on the science. However, there has generally been a steady evolution of key findings and levels of scientific confidence from one assessment report to the next.

The submission deadlines for the Fourth Assessment Report (AR4) differed for the reports of each Working Group. Deadlines for the Working Group I report were adjusted during the drafting and review process in order to ensure that reviewers had access to unpublished material being cited by the authors. The final deadline for cited publications was July 24, 2006. The final WG I report was released on April 30, 2007 and the final AR4 Synthesis Report was released on November 17, 2007.

Rajendra Pachauri, the IPCC chair, admitted at the launch of this report that since the IPCC began work on it, scientists have recorded "much stronger trends in climate change", like the unforeseen dramatic melting of polar ice in the summer of 2007, and added, "that means you better start with intervention much earlier".

Burden on participating scientists

Scientists who participate in the IPCC assessment process do so without any compensation other than the normal salaries they receive from their home institutions. The process is labor intensive, diverting time and resources from participating scientists' research programs. Concerns have been raised that the large uncompensated time commitment and disruption to their own research may discourage qualified scientists from participating.

Praise for IPCC

Various scientific bodies have issued official statements praising the IPCC and endorsing their findings.

The work of the Intergovernmental Panel on Climate Change (IPCC) represents the consensus of the international scientific community on climate change science. We recognise IPCC as the world's most reliable source of information on climate change and its causes, and we endorse its method of achieving this consensus.

We concur with the climate science assessment of the Intergovernmental Panel on Climate Change (IPCC) in 2001 ... We endorse the conclusions of the IPCC assessment...

CMOS endorses the process of periodic climate science assessment carried out by the Intergovernmental Panel on Climate Change and supports the conclusion, in its Third Assessment Report, which states that the balance of evidence suggests a discernible human influence on global climate.

The Intergovernmental Panel on Climate the main representative of the global scientific community....IPCC third assessment report...represents the state-of-the-art of climate science supported by the major science academies around the world and by the vast majority of scientific researchers and investigations as documented by the peer-reviewed scientific literature.

Internationally, the Intergovernmental Panel on Climate Change (IPCC)... is the most senior and authoritative body providing scientific advice to global policy makers.

The IPCC's conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue.

The IPCC should be congratulated for the contribution it has made to public understanding of the nexus that exists between energy, climate and sustainability.

In response to the release of the Fourth Assessment Report, the Royal Meteorological Society referred to the IPCC as “The world's best climate scientists”.

The most authoritative assessment of climate change in the near future is provided by the Inter-Governmental Panel for Climate Change.

See also

Notes and references

  1. The Nobel Peace Prize for 2007
  2. IPCC. . Retrieved December 19, 2006.
  5. Working Group 1, IPCC.
  6. Working Group 2, IPCC.
  7. Working Group 3, IPCC.
  8. Synthesis Report, IPCC.
  9. Headlines, IPCC.
  10. Working Group 1, IPCC.
  11. Castles and Henderson (2003), Energy & Environment, 14:159-185
  12. according to: Canadian Institute for Climate Studies, CCIS project: Frequently Asked Questions
  13. IPCC Special Report on Emissions Scenarios, Chapter 4: An Overview of Scenarios / 4.2. SRES Scenario Taxonomy / Table 4- 2: Overview of SRES scenario quantifications.
  14. Figure 2.11: Schematic illustration of SRES scenarios (IPCC)
  15. IPCC WG1, UCAR.
  16. Press release, IPCC, 2007-02-02.
  17. IPCC WGII web site
  18. Working Group II Contribution to the Intergovernmental Panel on Climate Change Fourth Assessment Report Climate Change 2007: Climate Change Impacts, Adaptation and Vulnerability: (23 page PDF file)
  20. IPCC. Official documents. Retrieved December 2006.
  21. IPCC. . February 19, 2006. Retrieved December 20, 2006.
  22. IPCC. . February 19, 2006. Retrieved December 20, 2006.
  23. IPCC. Mandate and Membership of IPCC. Retrieved December 20, 2006.
  24. Press flyer announcing 2007 report IPCC
  25. Working Group I press release IPCC via a copy at
  26. IPCC. Activities — Assessment Reports. Retrieved December 20, 2006.
  27. IPCC. Activities — Workshops & Expert Meetings. Retrieved December 20, 2006.
  28. IPCC AR4 WGI
  33. Welcome to the IPCC Data Distribution Centre
  34. IPCC - National Greenhouse Gas Inventories Programme
  35. Chris Landsea Leaves
  36. Follow Up: IPCC and Hurricanes
  37. Warning on Warming - The New York Review of Books
  38. Fox interview
  39. See main article on Stern Review
  40. Example of concerns over outdatedness of IPCC reports, see p.3
  41. Guidelines for inclusion of recent scientific literature in the Working Group I Fourth Assessment Report.
  42. Carbon Equity report on the Arctic summer of 2007
  43. Pachauri comments on worsening climate trends
  44. The Science of Climate Change from
  45. CFCAS Letter to PM, November 25, 2005
  46. CMOS Position Statement on Global Warming
  47. NOAA Global Warming FAQs
  48. Royal Meteorological Society's statement on the IPCC's Fourth Assessment Report.
  49. Global warming: a perspective from earth history

Further reading

External links

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