“Why don’t scientists just get together and figure out what’s going on?”

It’s a common question we hear about global warming.

The answer is simple:

“They have.”

The largest effort to pull the relevant research together is the series of assessment reports commissioned by the Intergovernmental Panel on Climate Change (IPCC).

The latest IPCC report on renewable energy was released yesterday, and will no doubt be open to much criticism. But will it be justified?

A mammoth effort

Given the amount of talk that goes on about climate change, it is perhaps surprising that so few people are aware of the IPCC, and the ones that do know so little about it.

The IPCC was set up by the UN in 1988 to assess the science for policy makers, releasing its first Assessment Report in 1990 and its fourth in 2007.

Each successive report has articulated more confidently that humans are changing the climate by emitting greenhouse gases, and that our current trajectory will bring much greater warming.

The warming predicted in 1990 has, so far, transpired on schedule.

Finding the facts, suggesting solutions

One thing many people don’t realise is that each report is actually in three volumes.

The first tackles the basic science: how much the earth has warmed, how much of it we caused, and what climate change to expect in the future.

The second concerns impacts and adaptation, for example impacts on crop yields or actions needed to protect coastal areas.

The last is about mitigation: how much it would cost to deal with the problem (or not to), and how might various policy and technological approaches pan out.

Each is written by a separate team of 200-plus authors and review editors chosen on the basis of their scientific accomplishments by an international nomination and evaluation process. They must serve on top of their “day jobs” as academics or other demanding positions.

These reports are massive, resembling a set of telephone books (though with flashier covers).

Receive, review, rewrite, negotiate, then start again

Their task is huge: to fairly and accurately assess all of the many thousands of peer-reviewed articles that have come out since the last report.

These are from a wide range of relevant scientific and technological disciplines including atmospheric physics and chemistry, oceanography, geology and economics.

Because it is an assessment, authors have leeway to express doubts about published work that is not deemed credible by the community.

Each report goes through several iterations of peer review. The 2007 report attracted 90,000 review comments, each of which required an individual response.

Preliminary drafts of the 2014 report have already been written but await two more years of revision and review.

The final step includes negotiations between scientist authors and non-scientist government representatives on the text of the report summaries (the parts non-scientists usually read).

Some authors have described these negotiations as harrowing, with a few governments driving hard to water down the findings.

Asking the experts

While climate contrarians often question the objectivity of the IPCC, the extensive review procedures leave little room for its conclusions to stray from those dominating the main scientific literature.

Each new report gets a different batch of expert authors - by now more than two thousand individuals have contributed.

Hardly a cabal of extremists, this is a hefty share of the world’s most qualified experts.

Several well-known contrarians have been authors, but constitute a tiny fraction of qualified experts and have therefore been unable to steer the conclusions (nor do they quibble with most of the contents anyway).

The range of reasonable views, discrepancies in published results, or lack of evidence on some issues are taken into account via the probabilistic language attached to report conclusions, although no claimed degree of uncertainty will ever satisfy everyone.

Nothing is claimed with absolute certainty, especially projections of the future.

Media hype hides the real story

News stories in 2010 hyped an error concerning Himalayan glaciers found on page 493 of the 2007 impacts volume.

There are probably more such errors buried in the main text, much of which is reviewed by only a few experts, but none has been reported in the important summaries, which receive far more scrutiny.

Nor have any errors been found in the volume of the report dealing with the basic science.

Another embarrassment came when the so-called “Climategate” emails seemed to show collusion among a few authors to exclude certain papers.

While these authors were hardly alone in doubting the validity of the papers in question, the papers were still ultimately included in the report, which if anything shows the report to be inclusive.

An InterAcademy Council Review of the body in 2010 suggested improvements, and criticised the impacts volume in particular, but did not find fundamental problems with the IPCC.

It’s hard to imagine a report free of any such glitches, but these have fuelled calls by conservative politicians in the US for an end to the IPCC.

An imperfect science, but an important one

Are the assessment reports alarmist, or too weak?

Instances can be found to support either view.

Conclusions can be weakened by the need to accommodate contrary views whether well-founded or not: for example, the 2007 report judged the 20th-century rise in CO2 only 90% likely to be human-caused, when the full brunt of evidence leaves no rational doubt of this.

And 11th-hour negotiations have on some occasions turned clear predictions of harm into meaninglessly vague ones.

On the other hand, many of the IPCC’s claims on current or future climate impacts rest on weak foundations or emphasise the worst possibilities.

To some extent this reflects the literature itself, the great difficulty in pinning down impacts rigorously, and perhaps, a feeling that we really should be looking at the worst possibilities.

It is (to use the IPCC’s uncertainty language) “highly likely” that the IPCC will continue to be criticised, mainly by those opposed to emissions reductions.

Its reports will never be perfect.

But they remain the ultimate compendia of climate knowledge, an unparalleled resource for scientists, students and punters alike, and are almost certainly the most thoroughly vetted scientific documents in history.

This author would be very happy to hear of a better alternative.