Assessing an IPCC assessment. An analysis of statements on projected regional impacts in the 2007 report

Key findings of IPCC on regional climate-change impacts overall considered well founded

The PBL Netherlands Environmental Assessment Agency has investigated the scientific foundations for the IPCC summary conclusions of the Fourth Assessment Report of 2007 on projected regional climate-change impacts, at the request of the Dutch Minister for the Environment. Overall the summary conclusions are considered well founded, none have been found to contain any significant errors. The Working Group II contribution to the Fourth Assessment Report shows ample observational evidence of regional climate change impacts, which have been projected to pose substantial risks to most parts of the world, under increasing temperatures.

However, in some instances the foundations for the summary statements should have been made more transparent. While acknowledging the essential role of expert judgment in scientific assessments, the PBL recommends to improve the transparency of these judgments in future IPCC reports.

In addition, the investigated summary conclusions tend to single out the most important negative impacts of climate change. Although this approach was agreed to by the IPCC governments for the Fourth Assessment Report, the PBL recommends that the full spectrum of regional impacts is summarised for the Fifth Assessment Report, including the uncertainties.

The PBL believes that the IPCC should invest more in quality control in order to prevent mistakes and shortcomings, to the extent possible.

The Dutch Parliament resolution and the subsequent assignment given to the PBL

In January 2010, worldwide media attention was given to two errors that had bee discovered in a part of the Fourth Assessment Report of the IPCC of 2007: an erroneously high rate of melting of the Himalayan glaciers, and an erroneously high percentage of land area in the Netherlands lying below sea level. The commotion in the Dutch media and the subsequent discussion at the political level in the Netherlands led to a resolution by the Dutch Parliament on 28 January 2010, which declared in the preamble that the reliability of the IPCC should be undisputed but was now at issue. In the resolution, the parliament required that the government would instruct the Netherlands Environmental Assessment Agency (PBL) to provide a new update on climate science, including the implications of the said errors.

Based on this resolution and the debate in parliament, the Minister for the Environment decided to limit her question to PBL to an investigation in the implications of possible errors in the regional chapters of the IPCC report of 2007 on climate-change impacts, adaptation and vulnerability, paying specific attention to the Himalayan glaciers.

Supervision Royal Netherlands Academy of Arts and Sciences

This project has been conducted under the supervision of an independent commission of the Royal Netherlands Academy of Arts and Sciences (KNAW).

Registration website

The PBL launched a public website (in Dutch) that would be available for the course of one month, in order to give all experts in the Netherlands the opportunity to contribute to our investigation. We asked for submissions of possible errors found in regional chapters of the Working Group II Report. By the end of that month, the PBL had registered some 40 submissions; however, most of them were about issues related to the Working Group I Report. Three submissions qualified to be addressed in our report. All submissions and PBL’s responses have been published on the PBL website.