The IPCC Fourth Assessment Report (AR4) is a report on climate change created with the help of a large number of contributors, both scientists and governmental representatives. There has been considerable political controversy over errors found in the report, and there have been calls for review of the process used to formulate the report.
Content issues Some observers have identified issues in which the peer-reviewed science suggests outcomes more severe than outlined by the report, while other observers have said that some conclusions in the report are not satisfactorily supported by the peer-reviewed science. The Intergovernmental Panel on Climate Change (IPCC) have acknowledged that a paragraph in the WGII report on the projected date of melting of Himalayan glaciers is incorrect. Climate expert Martin Parry, who had been co-chair of the working group on impacts for IPCC AR4, stated that "What began with a single unfortunate error over Himalayan glaciers has become a clamour without substance". The IPCC had investigated other alleged mistakes, which were "generally unfounded and also marginal to the assessment", and were commonly based on the idea that the IPCC should not use grey literature, such as reports from campaign groups and governments.
Arctic sea ice extent
According to a study conducted by the National Center for Atmospheric Research and the National Snow and Ice Data Center, Arctic Sea ice is melting faster than predicted by climate models. The study concludes that the 18 models on which the IPCC has based its current recommendations could already be out of date, and that the retreat of the ice could already be 30 years ahead of the IPCC's worst-case scenario, possibly leading to an ice-free summer Arctic before the end of the 21st century.
Glacial dynamics
The IPCC AR4 estimates explicitly exclude the influence of the melting of ice sheets.This contrasts with the IPCC AR3, which included earlier estimates of these ice dynamics, and had a higher top end sea level rise estimate, although much lower than some new estimates. The report states that recent observations suggest that ice flow dynamics could lead to additional rise: "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. Understanding of these processes is limited and there is no consensus on their magnitude." These ice sheets include most notably the Greenland ice sheet, and both the east and west Antarctic ice sheets, as well as numerous glaciers. This may result in a major underestimate of the upper limit for sea level rise in the long term. Due to Arctic melting the Greenland ice sheet is particularly vulnerable, and a study by climatologist James E. Hansen states that "we cannot rule out large changes on decadal time-scales once wide-scale surface melt is underway." The melting of the Greenland ice sheet would result in an increase in sea level rise of over 7m.Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) [Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881pp. ,, and . Melting of the west Antarctic ice sheet would cause a similar, if slightly smaller rise in sea levels due to being grounded below sea level, whilst the effect of the melting of the east Antarctic, although less probable would be an order of magnitude greater.
In a lecture he gave at the University of California, Santa Barbara, James E. Hansen criticised the IPCC for its description of future sea level rise. Hansen has also written on this issue:
The IPCC [Working Group I] (2007) midrange projection for sea level rise this century is 20–43 cm (8–17 inches) and its full range is 18–59 cm (7–23 inches). The IPCC notes that they are unable to evaluate possible dynamical responses of the ice sheets, and thus do not include any possible 'rapid dynamical changes in ice flow'. Yet the provision of such specific numbers for sea level rise encourages a predictable public response that the projected sea level change is moderate, and smaller than in IPCC (2001). Indeed, there have been numerous media reports of 'reduced' sea level rise predictions, and commentators have denigrated suggestions that business-as-usual greenhouse gas emissions may cause a sea level rise of the order of meters
... The IPCC is doing a commendable job, but we need something more. Given the reticence that the IPCC necessarily exhibits, there need to be supplementary mechanisms. The onus, it seems to me, falls on us scientists as a community.
In a lecture given at Princeton University, IPCC author Michael Oppenheimer admitted that the IPCC report could have better explained the contribution of melting ice sheets in predictions of sea level rise. Oppenheimer said that the IPCC Working Group II Summary for Policymakers (quoted below) managed this better than the Working Group I Summary for Policymakers:
There is medium confidence [about 5/10 chance of being correct] that at least partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic ice sheet, would occur over a period of time ranging from centuries to millennia for a global average temperature increase of 1–4°C (relative to 1990–2000), causing a contribution to sea-level rise of 4–6 m or more.
Projected date of melting of Himalayan glaciers
A paragraph in the 938-page 2007 Working Group II report (WGII) included a projection that Himalayan glaciers could disappear by 2035. This projection was not included in the final summary for policymakers which highlighted the importance of the glaciers for freshwater availability, and stated that "Widespread mass losses from glaciers and reductions in snow cover over recent decades are projected to accelerate throughout the 21st century". Late in 2009, in the approach to the Copenhagen climate summit, the 2035 date was strongly questioned in India. On 19 January 2010 the IPCC acknowledged that the paragraph was incorrect, while reaffirming that the conclusion in the final summary was robust. They expressed regret for "the poor application of well-established IPCC procedures in this instance" and their vice-chairman Jean-Pascal van Ypersele said that the reviewing procedures would have to be tightened.
The WGII report ("Impacts, Adaptation and Vulnerability"), chapter 10, page 493, includes this paragraph:
There was controversy in India over this statement, and at the start of December 2009 J. Graham Cogley of Trent University, Ontario, described the paragraph as wildly inaccurate. The rates of recession of Himalayan glaciers were exceptional, but their disappearance by 2035 would require a huge acceleration in rate. The first sentence of the IPCC WGII report, including the date of 2035, came from the cited source, "(WWF, 2005)". This was a March 2005 World Wildlife Fund Nepal Program report, page 29:
On page 2, the WWF report cited an article in the 5 June 1999 issue of New Scientist which quoted Syed Hasnain, Chairman of the International Commission for Snow and Ice (ICSI), saying that most of the glaciers in the Himalayan region "will vanish within 40 years as a result of global warming". That article was based on an email interview, and says that "Hasnain's four-year study indicates that all the glaciers in the central and eastern Himalayas could disappear by 2035 at their present rate of decline." Both the article and the WWF report referred to Hasnain's unpublished 1999 ICSI study, Report on Himalayan Glaciology, which does not estimate a date for the disappearance of Himalayan glaciers.
The second sentence of the questionable WGII paragraph which states "Its total area will likely shrink from the present 500,000 to 100,000 km2 by the year 2035" could not refer to the Himalayan glaciers, which cover about 33,000 km2. Cogley said that a bibliographic search indicated that it had been copied inaccurately from a 1996 International Hydrological Programme (IHP) report by Kotlyakov, published by UNESCO, which gave a rough estimate of shrinkage of the world's total area of glaciers and ice caps by 2350.
Cogley suggested that the "2035" figure in the second sentence of the WGII paragraph was apparently a typographic error. He concluded, "This was a bad error. It was a really bad paragraph, and poses a legitimate question about how to improve IPCC's review process. It was not a conspiracy. The error does not compromise the IPCC Fourth Assessment, which for the most part was well reviewed and is highly accurate."
Statements very similar to those made in both sentences of the WGII paragraph appeared as two successive paragraphs in an April 1999 article in Down to Earth , published in the India Environment Portal (IEP). This included the substitution of 2035 for 2350 as stated in the IHP study. New Scientist has drawn attention to Hasnain's claim about the timing of glaciers disappearing:
The question of whether it was acceptable to use material which had not been peer reviewed has been disputed. IPCC rules permit the use of non-peer-reviewed material, subject to a procedure in which authors are to critically assess any source that they wish to include, and "each chapter team should review the quality and validity of each source before incorporating results from the source into an IPCC Report."
The official statement issued by the IPCC on 20 January 2010 noted that "a paragraph in the 938-page Working Group II contribution to the underlying assessment refers to poorly substantiated estimates of rate of recession and date for the disappearance of Himalayan glaciers. In drafting the paragraph in question, the clear and well-established standards of evidence, required by the IPCC procedures, were not applied properly." It emphasised that the paragraph did not affect the conclusion in the final summary for policymakers in the 2007 report, which it described as "robust, appropriate, and entirely consistent with the underlying science and the broader IPCC assessment", and reaffirmed a commitment to absolute adherence to the IPCC standards. The IPCC also stated that it did not change the broad picture of man-made climate change. This was confirmed by Wilfried Haeberli, who announced the latest annual results of the World Glacier Monitoring Service. He stated that the important trend of 10 years or so showed "an unbroken acceleration in melting" and on expected trends, many glaciers will disappear by mid century. Glaciers in lower mountain ranges were the most vulnerable, and while those in the Himalayas and Alaska could grow in the short term, in a realistic mid-range warming scenario they would not last many centuries. Mojib Latif, a climate scientist who contributed to the report of Working Group 1, sees the consequences of the glacier data mistake but also the need to continue focusing on global warming.
African crop yield projections