Fiona Harvey Climate science: the IPCC controversy explained

The ongoing storm over climate change science is cheering up climate change sceptics no end. What with last November’s email scandal (in which emails sent among climate scientists were hacked and exposed on the web), the chaotic scenes at Copenhagen in December, and last month’s revelations about shortcomings on the part of the Intergovernmental Panel on Climate Change, it’s been a heady few months for the sceptics.

But before we get carried away, let’s examine some of the claims against climate science more closely.

Take the IPCC first. In early January, the New Scientist reported that a claim in the 2007 IPCC report on climate change – that the Himalaya’s glaciers could lose most of their mass by 2035 – was based on a report by WWF, which in turn was based on the New Scientist’s account of an interview it held with an Indian glaciologist in 1999. The expert in question did not repeat the claim in any peer-reviewed study.

To cite such a source for such a dramatic claim was certainly a bad mistake by the IPCC, and shows reprehensible sloppiness.

But to put the claim in context, it’s important to understand how the IPCC works.

The 2007 report was divided into three: one part on the basic science of climate change, the second on the impacts that climate change would have on natural systems and human infrastructure, and the third on the economics of climate change and what to do about it. The glaciers claim was one line in the second section of the report, which ran to about 1,000 pages.

In drawing up the report, the hundreds of authors draw on an immense range of sources. Thousands of scientists have an input, scouring tens and even hundreds of thousands of pieces of research, and years of extensive work may yield only a few lines that make it into the report. Conversely, drawing the net so widely means that reports that have not been subjected to the most rigorous review can also be included – again, mostly they are granted a line or two.

This produces the 1,000 page comprehensive report – so comprehensive that a good proportion of the views in it are those of climate sceptic scientists. Lord Monckton, for instance, the prominent British climate sceptic, boasts of being an IPCC author (athough the claim is partly tongue-in-cheek, as his contribution was a letter pointing out a typographical error). Other sceptics who are IPCC authors included Richard Lindzen of the Massachusetts Institute of Technology and John Christy.

As a result of this extraordinarily wide range of views, many sceptical scientists have no quarrel with this part of the IPCC process.

After all, if all of the information included in the report had to be peer-reviewed, many of the sceptics’ papers would not make it in, as some of them have not passed peer review. This is a very important point to make.

It is only by including non-peer-review material, then, that the IPCC can claim to be comprehensive.

Where sceptics often start to disagree with the IPCC process is the next stage: when these thousand pages are distilled to a technical summary and from that to a short “summary for policymakers”, or SPM for short. At this point, a smaller number of scientists reviews the chapters and draw from them the most important conclusions.

This is the crucial document from the IPCC – the SPM is what is presented to governments, and its findings are used to inform the international negotiations on a global response to climate change. The SPM is, in short, the gold standard.

In drawing the conclusions for the SPM, the scientists apply more robust methodologies than are applied to the inclusion of data into the wider report. The predictions that make it into the summary for policymakers are only those that are most widely supported by different data sources – that is, where many pieces of research point in the same direction.

It’s also important to note that, in part for this reason, the Himalayan glacier claim never made it into the summary for policymakers. (And a search of world media outlets shows that, until last month, the Himialayan claim had only been referred to a handful of times, suggesting it did not have very much impact – and indeed most claims that are not included in the SPM do not get much attention, as the SPM is recognised as the crucial document.)

Sceptics complain that their findings are often left out of the SPM. Other climate scientists frequently complain that their findings showing that the dangers of climate change are far greater than had been presumed are also left out.

In other words, only the mainstream findings have a chance of making it in to the SPM, the ones that have most backing.

There is one final stage to the SPM. Before it can be published, every government in the world has the right to send a delegation to the meeting where it is discussed. (These delegations need not be made up only of scientists, moreover, and some countries send very large delegations – China was reported to have sent nearly 50 people in 2007.)

Every word of the SPM must be approved by every government present before it can be published. This makes for a long process in which governments wrangle and haggle about every adjective, comma and full stop. And critics say it produces a document that is bland and does not reflect the diversity of opinion among scientists. But it does produce a document that no government can then deny, because all have agreed it.

This arduous and convoluted process is designed to ensure that the SPM contains only substantiated data and can be relied on by policymakers.

The fact that the Himalayan claim was not in the SPM is, therefore, very important in judging how serious a mistake was its inclusion in the wider report.

The answer has to be – not as serious as some have been making out, especially when you consider that some less substantiated work by climate sceptics is also included in the wider report. Would the most vocal critics of the IPCC be prepared to see those excised from any future report as well?