So there it is. The latest report from the Intergovernmental Panel on Climate Change (IPCC) has gone further than any of its predecessors in showing that global warming is already affecting the whole globe.

It reports that evidence of its impact can be found “on all continents and across the oceans” and adds that the world is “in many cases ill-prepared for risks form a changing climate.” And it warns that allowing it to continue will increase the risk of “severe, pervasive and irreversible” consequences, including “violent conflict” as people compete for dwindling resources.

Wheat yields, for example, have already suffered and could drop by a quarter between 2030 and 2049, it says, while “all aspects of food security are potentially affected.”, while the price of food could rise by up to 84 per cent by 2050.

In being quite so stark the IPCC is confounding expectations. Not, let it be said, by exaggerating the science; far, from it – as the work of over several hundred scientists and the world’s governments – the report is a consensus document and thus will have necessarily tended towards understatement. The surprise is that the panel has been courageous enough to tell it as it is, for the IPCC has had quite a bashing since last it reported seven years ago, and both scientists and governments are pretty timorous creatures by nature.

The equivalent of this report, in 2007, was found to contain a few errors – most notably an uncharacteristic exaggeration of the rate at which glaciers are melting in the Himalayas – that were used to discredit the whole process. It looked for a while as if the badly bruised scientists would seek to avoid any further unpleasantness by pulling their punches.

And there was an even worse prospect. The IPCC’ s chairman, Rajendra Pachauri, had greatly compounded the crisis by a bombastic response to the exposure of the errors, gravely damaging his own credibility in the process. It was feared that the upshot would be that a toned-down report would end up being presented by a chairman (wrongly) suspected of exaggerating.

In the end, neither has happened. The report spells out the (consensual) science, while Dr Pachauri has been far less visible than the scientists that wrote the report, notably Prof Chris Field of Stanford University, one of the co-chairs of the working group that produced it.

And the tide of scepticism that began flooding in at the time of the crisis, now seems to be receding, not least because of the very observation of effects of climate change that the report describes. One survey, by the Benenson and GS strategy group found last summer that even 53 per cent of young US Republican voters saw “climate change deniers” as “ignorant”, “out of touch” or just plain “crazy”.

Of course it could all yet blow up. Global warming sceptics will go through the report with a fine tooth comb looking for mistakes they can highlight (though the Himalayan howler last time was exposed not by them but by climate scientists). But there are signs, as the world enters a crucial 20 month rundown to the next big bid to reach a new international agreement on combating climate change, that the political tide may be changing.

My weekend Telegraph column, written before the publication of the report, explores this further and concludes that there may now be a more realistic basis on which to build agreement than amid the optimistic atmosphere that pervaded the run-up to the ill-fated 2009 Copenhagen climate summit.

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