The U.N.'s Intergovernmental Panel on Climate Change (IPCC) screwed up.
The IPCC describes itself as "the leading body for the assessment of climate change, established ... to provide the world with a clear scientific view on the current state of climate change and its potential environmental and socio-economic consequences."
Tapping the help of thousands of scientists the world over, the group produces comprehensive climate science assessments. To assure accuracy and balance, its rules are very clear: findings from the peer-reviewed literature are are given priority, and reports are subjected to peer and governmental review. There are also clearly defined procedures for including non-peer-reviewed literature, when necessary, which include "critical assess[ment]."
For these reasons, climate scientists often point to IPCC assessments as the "final word" on global warming -- an attribute that's been called into question by the revelation that the IPCC inaccurately stated the Himalayan glaciers would be gone in a few decades.
Much has been written about the error in the IPCC report (see here, here and here). On January 20, the IPCC issued its own statement [pdf] that reads in part:
"It has ... recently come to our attention 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."
Actually the IPCC had a lot to say about Himalayan glaciers in its latest report -- some accurate, some not. Comparing these various statements provides some insight into the IPCC process and what went wrong.
The IPCC Report Is Not Just One Report
The IPCC has now produced four separate assessments. The first (FAR) was released in 1990, the second in 1995 (SAR), the third in 2001 (TAR), and the fourth (AR4) in 2007. A fifth (AR5 [pdf]) is slated for publication in 2013 or 2014.
The AR4 assessment actually consists of four separate reports:
- Working Group 1 (WG1) on the Physical Science Basis, including the evidence of warming and causes,
- Working Group 2 (WG2) on Impacts, Adaptation and Vulnerability,
It's important to bear in mind that each report is written by a different team, so there can be inconsistency between them. Such was the case for Himalayan glaciers.
WG1 Report -- Balanced and Careful
Section 4.5 of the WG1 report covers the subject of glaciers in careful, balanced wording. Examples:
"Mass loss of glaciers and ice caps is estimated to be 0.50 ± 0.18 mm yr in sea level equivalent (SLE) between 1961 and 2004, and 0.77 ± 0.22 mm yr SLE between 1991 and 2004. ... [T]he biggest contributions to sea level rise came from Alaska, the Arctic and the Asian high mountains." (Executive Summary, p. 339)
"Whereas glaciers in the Asian high mountains have generally shrunk at varying rates (Su and Shi, 2002; Ren et al., 2004; Solomina et al., 2004; Dyurgerov and Meier, 2005), several high glaciers in the central Karakoram are reported to have advanced and/or thickened at their tongues (Hewitt, 2005), probably due to enhanced precipitation." (p. 360).
Factual and just a tad dull, but nothing about glacier disappearance by 2035.
WG2 Shows Some Cracks
In Section 10.6 of WG2, problems arise in actually two offending statements:
1. "Himalayan glaciers cover about three million hectares or 17% of the mountain area as compared to 2.2% in the Swiss Alps. They form the largest body of ice outside the polar caps and are the source of water for the innumerable rivers that flow across the Indo-Gangetic plains ... the lifeline of millions of people in South Asian countries (Pakistan, Nepal, Bhutan, India and Bangladesh). The Gangetic basin alone is home to 500 million people, about 10% of the total human population in the region."
2. "Glaciers in the Himalaya are receding faster than in any other part of the world (see Table 10.9) and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high if the Earth keeps warming at the current rate (WWF, 2005)."
That first statement (made without attribution) about glaciers being a water source in the Indo-Gangetic plains for 500 million people is technically true but misleading -- perhaps even alarmist. Actually the monsoons are the region's primary source of water; the glaciers, while providing only a small portion of the total water supply, are a key source during the dry season.
The second statement, attributed to a report by the World Wildlife Fund (hardly a peer-reviewed journal), simply has no basis in fact.
Summaries Did Not Propagate the Mistake
It is fascinating to see that WG2's misstatements do NOT appear in its summary for policy makers. Here's what is said about the Himalayas there:
"Glacier melt in the Himalayas is projected to increase flooding, and rock avalanches from destabilised slopes, and to affect water resources within the next two to three decades. This will be followed by decreased river flows as the glaciers recede."
The coverage of the Himalayas in the Synthesis Report hews closer to findings reported in WG1 than those in WG2:
"Widespread mass losses from glaciers and reductions in snow cover over recent decades are projected to accelerate throughout the 21st century, reducing water availability, hydropower potential, and changing seasonality of flows in regions supplied by meltwater from major mountain ranges (e.g. Hindu-Kush, Himalaya, Andes)" (p. 49)
What Happened?
While IPCC assessments are supposed to be consensus reports, it is clear that the contention that the Himalayas were slated to disappear by 2035 was not the consensus of the scientists who worked on the IPCC. It is unfortunate that, perhaps because it was the most sensational, the disappearing-by-2035 statement about the Himalayas was the one that got the most attention.
This is not a time for the scientific community to circle the wagons and try to explain away this error, but rather to understand what happened. One thing seems clear: the AR4 was such a massive report that most of the scientists in the IPCC had no idea of what was being said in a small section of the WG2's tenth chapter.
But where were the glaciologists who would have known better than to include the WG2 claims? A colleague told me that the glaciologists were working on the much more measured and balanced WG1 report, and did not see the WG2 report and perhaps were not even asked to review it. Even more troublesome are reports (e.g., here and here) that the IPCC leadership responded defensively to criticism of the statements in question rather than consulting with the experts. If so, these were glaring mistakes.
Despite these errors, there is an awful lot in the AR4, especially in the measured and carefully worded WG1 report (which I know the most about), that is rock-solid. And the gravity of shrinking glaciers whose ice loss is well documented should not be dismissed.
Nevertheless, people will ask, and justifiably, how many more gaffes are hiding in the IPCC reports? Is the answer that the "exception proves the rule"? To make it so, the IPCC's got some explaining to do, and I don't think its January 20th statement does the trick.
Correction: February 3, 2010.
This post was updated to reflect the fact that IPCC rules do allow non-peer-reviewed literature, when necessary.