No country will be immune from the impact of global warming but in Britain the effects will not be all bad. More flood defences will be needed and some coastal areas may have to be surrendered to rising sea levels. Road surfaces and railway tracks that are resistant to intense heat may also have to be introduced.

But there will be significant benefits. Harvests of cereal crops such as wheat could improve greatly, many people will welcome Mediterranean summers and, if James Lovelock, the creator of the Gaia theory, is to be believed, Britain will become an even bigger centre for business and investment.

However, the report takes a global view and, for the most part, makes bleak reading. While Britons top up their tans in 2100, billions of other people, it predicts, will have died, suffered or been driven from their homes unless global warming is brought under control.

They will battle with increased disease rates, struggle to find water and watch their crops fail. They will see the landscape dry out around them as rainfall levels slump and are likely to experience the miseries of wars over water rights. They can expect the wrath of nature, too, as hurricanes and typhoons become more common, more intense and more devastating.

For the most part those who will suffer are the world’s poorest. In Africa alone 75 million to 250 million people are predicted to endure water shortages by 2020. In large parts of Asia a billion people will experience freshwater shortages by the 2050s.

The report identifies as essential both adaptation measures, designed to cope with the effects of climate change, and mitigation measures, aimed at reducing the quantities of carbon dioxide and other greenhouse gases going into the atmosphere.

The importance of the report is that it establishes solid scientific evidence, not only for what is likely in coming years, but what is happening now. It illustrates that climate change is with us, not some distant threat.

World leaders and other politicians need such evidence to persuade them that something must be done, and then as a baseline to guide policies to tackle climate change effectively.

Interest groups such as Friends of the Earth, Greenpeace and the WWF gave the report a broad welcome but, mixed with appreciation, were warnings that it must be heeded and acted upon, not filed away in a dusty drawer. Also welcoming were the World Health Organisation and aid agencies, all worried about the extra burden that climate change will place on developing countries, and so on them.

Their determination that the report should be a springboard to action was shared by Lord Rees of Ludlow, the President of the Royal Society, who called it “another wake-up call for governments, industry and individuals”. Sadly, he is right. It is hardly the first alarm bell to be sounded about the dangers of climate change.

The determination of nations such as China and India to confront the scientists over their conclusions as the report was being put together indicates that there is some way to go before a consensus can be reached. Nevertheless, that they and scores of other government delegations signed up to the report is at least a cause for hope.