---
title: "Criticism of the IPCC Fourth Assessment Report"
chunk: 1/5
source: "https://en.wikipedia.org/wiki/Criticism_of_the_IPCC_Fourth_Assessment_Report"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:22:45.688900+00:00"
instance: "kb-cron"
---

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 The study concludes that the 18 models on which the IPCC has based its current recommendations could already be out of date, and that the retreat of the ice could already be 30 years ahead of the IPCC's worst-case scenario, possibly leading to an ice-free summer Arctic before the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. 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.  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: