No significant errors in the 4th IPCC report on climate, according to a Dutch study

The full document can be found on :

 Excerpts from the executive summary of the Agency report selected by GreenFacts

The Netherlands Environmental Assessment Agency (PBL) 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 and none were found to contain any significant errors.

The Netherlands Environmental Assessment Agency (PBL) is an independent governmental body that by statute provides the Dutch Government and Parliament – and the European Commission, European Parliament and UN organisations – with scientific advice on problems regarding the environment, sustainability and spatial planning.

Context : In January 2010, the media reported two errors in specific parts of the Fourth Assessment Report of 2007 by the Intergovernmental Panel on Climate Change (IPCC). The media reports gave rise to questions about the credibility of the overall IPCC assessment: could politics and society still rely on the IPCC for an assessment of the scientific knowledge on climate change?

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

 No significant errors found in summary conclusions

The foundations for thirty-two IPCC Fourth Assessment summary conclusions

on the regional impacts of climate change have been investigated. These conclusions show examples of projections of climate-change impacts on food, water, ecosystems, coastal regions and health, for all the earth’s continents.

These conclusions have not been undermined by errors, although one of the conclusions contains a minor inaccuracy: in hindsight, not 75 to 250 million people, but 90 to 220 million people are projected to be exposed to increased water stress due to climate change in Africa, by 2020. Given the large uncertainties surrounding such projections, this difference is not significant.  Provenance of summary statements needs to become more transparent in future reports

For two of these conclusions, the PBL critical comments pertain to insufficiently founded generalisations from existing scientific research, in both cases from local to regional scales, and for one of them also from one type of livestock to livestock in general.

The regional chapters: one significant error and some comments

In the underlying regional chapters, in addition to the two already known errors about the melting of the Himalayan glaciers and about the Dutch land area below sea level, another significant error was found: a 50 to 60% decrease in productivity in anchovy fisheries on the African west coast was projected on the basis of an erroneous interpretation of the literature references. It appeared to be about a 50 to 60% decrease in extreme wind and seawater turbulence, with some effects on the anchovy population that were not quantified.

The PBL found certain inaccuracies, ranging from (very) small errors in numbers to imprecise literature references. In addition, the PBL has some critical comments to make. One of these relates to the fact that the report does not specify how many of the additional heatrelated deaths projected for Australian cities are actually attributable to climate change – a sizeable fraction is due to demographic changes alone. However, these shortcomings do not affect the investigated 32 summary conclusions or other parts of the IPCC summaries.

Examples of negative impacts dominate at summary level

The IPCC Working Group II Report focuses on climate impacts, adaptation and vulnerability. It was found by the PBL that, in the IPCC’s highest level summary, the conclusions that were derived from the regional chapters of the Working Group II contribution to the Fourth Assessment Report single out examples of projections of negative climate-change impacts. The IPCC authors considered these to be the most relevant to policymakers. The PBL has labelled this as a ‘risk-oriented’ approach, which had been implicitly endorsed by the governments that constitute the IPCC (including that of the Netherlands).

The PBL subscribes to the importance of an approach that highlights what may go wrong under unmitigated climate change, but the Working Group II Report lacked a clear explanation of the choice of approach and its consequences. Alternatively, it could be argued that policymakers should be presented with a complete picture in the Summaries for Policymakers, not just with negative examples (without suggesting that potential positive effects cancel out potential negative effects). We recommend that, for the Fifth Assessment Report, the choice of the approach taken is made explicit.

No consequences for overarching conclusions

The PBL findings do not contradict the main conclusions of the IPCC on impacts, adaptation and vulnerability related to climate change. There is ample observational evidence of natural systems being influenced by climate change on regional levels. The negative impacts under unmitigated climate change in the future pose substantial risks to most parts of the world, with risks increasing at higher global average temperatures.

Other recommendations

The PBL made additional recommendations for future IPCC publications which include:

– to create a public website for the submission of possible errors found in the published reports;  In particular to ensure that statements that attribute impacts to climate change are well founded in scientific research, including systematic observations, modelling and statistics.

– that the climate change component of impacts should be carefully characterised. It recommends also to be careful with phrasing of statements that could be perceived by readers as  heightening the projected impacts of climate change.

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

©Netherlands Environmental Assessment Agency (PBL)  The Hague/Bilthoven, 2010 PBL publication number: 500216002 Cover photo: Hollandse Hoogte Corresponding author: This publication can be downloaded from: A hard copy may be ordered from:, citing the PBL publication number or ISBN.

To discover further underlying scientific facts related to climate :

– read the GreenFacts  summary of the IPCC’s Fourth Assessment Report – also available in Dutch, French and Spanish

– read also several related  GreenFacts  “Digests” available through our Climate change Theme page
addressing for instance energy technologies, biofuels and CO2 capture and storage.

Note : the content of the shorts reports of the blog are not verified by the Scientific Board

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