The wake-up call the world so urgently needs on global warming has been delivered by former World Bank chief economist Sir Nicholas Stern. His 700-page report on the global impact of rising temperatures does what no agreement, policy, speech, book or film has yet done so thoroughly: laid bare the economic consequences for the world if all nations do not work together to combat the problem. Sir Nicholas' high profile makes the document important. It has been backed by the British government. The significance of the report was raised even higher by the fact that its release came on the day the UN revealed a continued rise in greenhouse gas emissions by industrialised nations and a week ahead of a UN meeting that will take up the divisive issue of what happens when the Kyoto Protocol on climate change ends in 2012. The report is wide-ranging and many faceted, but the essence is straightforward: inaction will cost the world much more than the relatively small price of doing something now. Sir Nicholas makes assumptions and works in estimates because the science of global warming is still new, but has evidence on his side; temperatures are clearly rising and, as former US vice-president-turned-environmentalist Al Gore dramatically shows in his documentary An Inconvenient Truth, emissions of carbon dioxide and other greenhouse gases are largely to blame. Cost has always been the problem for the US and Australia, the world's biggest per capita producers of greenhouse gases and the main holdouts to the Kyoto Protocol. They argue that the pact's provisions of cutting emissions harm industrial output and, consequently, economic growth. Sir Nicholas agrees, saying that the effort needed to reduce emissions through technology and changing practices will amount to about 1 per cent of gross domestic product. But to not make an effort to keep temperatures from rising by the estimated 2 to 3 degrees Celsius by 2050 will have far graver economic consequences, believed to be on a par with a world war or the depression of the 1930s. People the world over would be between 5 and 20 per cent financially worse off than they are now, depending on how high temperatures rise. The estimates are based on annual emissions remaining at present levels, which means that in 2050, the amount of greenhouse gases in the atmosphere would be 550 parts per million by volume - determined by the economist to be 'potentially dangerous'. Present carbon dioxide levels are 380ppm and Sir Nicholas suggests that a level of between 500ppm and 550ppm would be 'significant, but manageable'. To achieve this minimum, immediate, radical, reforms would be necessary, including the taking up of clean power and transport technologies, storing of carbon emissions underground, increased public spending on research and development and the substantial raising of incentives. Whether these measures will be sufficient is a matter of guesswork. Some environmental campaigners contend we need to reduce greenhouse gas emissions by 90 per cent to achieve safe levels. This is up to 30 per cent beyond Sir Nicholas' calculations and the costs of achieving such a goal could be economically crippling. Governments could ignore Sir Nicholas' report and, like the US and Australia, go our own, voluntary, ways. It is obvious, though, as the report says, the problem is a global one and not something that can be dealt with by some countries while others choose a different approach. Nor, as Kyoto allows, should developed nations participate while other, increasingly polluting ones such as China, India and Brazil, be immune if they so wish. Delegates to the forthcoming UN meeting in Nairobi must use the economist's report as a key guide in determining the way ahead in slowing or stopping global warming. Any post-Kyoto framework has to include all nations. Whatever they determine has to be agreed to quickly. As Sir Nicholas warns, the problem of global warming is not going to go away without a concerted, international effort.