Six years and a quantum leap in global concern have passed since the release of the previous report of the Intergovernmental Panel on Climate Change (IPCC). Today the first part of its fourth assessment report (AR4) is released in Paris.

Over 800 authors contributed to the latest report, which represents the most comprehensive summary of the international research in climate and climate-related disciplines available. It consists of three working groups – the first, the report of which is released today, assesses scientific aspects of climate change (including detection, attribution and projection of change), the second its expected impacts, and the third mitigation options.

Since the final IPCC report is intended to provide information for policy makers, the review process is an unusual one – after being effectively subject to several levels of scientific review (AR4 involved more than 2,500 reviewers), the text then undergoes what might be termed “political” review. And given the implications of the content, last minute wrangling over the final wording of the reports can be intense.

Delegates who perceive their nations as having the most to lose financially from emissions reductions (for example, the big OPEC producers, the US and China) naturally push for semantic wiggle room, while those that expect to face the most serious impacts (eg. the small island and African states) are likely to push for a stronger, less ambiguous treatment.

It ought to make for some red eyes in Paris today. But it can go further than semantics. Last week The Guardian reported on the US push to include more discussion on the benefits of both voluntary emissions agreements and geo-engineering mitigation options in the final report.

Arguments behind closed doors are one thing. But given the newfound public profile of the climate issue, AR4 is already making a much larger media splash than the IPCC’s previous reports, and opinion has moved so far on the issue that the political response amongst the nations still — as Tim Flannery puts it — “dragging the chain” is likely to be largely unquestioning of the final report’s substance.

Electoral concerns are something that the sceptic camp (who’ve now rebranded themselves climate “rationalists”) needn’t worry about. To many of them, the IPCC is the very beating heart of the climate conspiracy — Pope Urban to their (well-funded by industry) Galileo — and they have been unremitting in their attacks on the IPCC in the past.

The fact that the IPCC process unavoidably results in disagreement and occasional acrimony is often held up as an indication that it doesn’t work. My view would be that the tortuous review process and consensus-based approach is precisely what gives the IPCC report its value – it’s not perfect, but it is worth emphasising that the outcome is a decidedly conservative assessment. In mainstream scientific circles, this is not a controversial statement.

One of those who came in for strident criticism in the third assessment report (TAR) was Michael Mann, the lead researcher on a study that used proxy climate data (including ice core and tree ring analysis) to make estimates of global temperatures reaching back to the tenth century. His data figured prominently in the TAR, and the graph became known as the “Hockey Stick” (see here). On the back of this criticism the IPCC process was denounced in many quarters as flawed beyond repair.

As the above article details, Mann’s research was largely exonerated by the US National Academy of Sciences, though the rationalists would probably spray their coffee over that statement (doubtless I’ll read your comments tomorrow – Napisan is great for coffee stains).

It will be interesting to see their response – on the one hand, their message is less likely to be well-received by the public, but on the other, media reports this week demonstrate the level of impact the IPCC report is likely to have.