Dealing with the impact of a warmer world

Experts and policymakers will gather in Brussels next week to discuss a world that is two or three degrees warmer, in which millions will be without water, tens of millions displaced by floods, tropical diseases could multiply and some species will die out.

They will be given a glimpse of how the world might be in just 50 years, as laid out in a draft of the next piece of work to emerge from the UN’s Intergovernmental Panel on Climate Change (IPCC).

The final version of the report of the IPCC’s second working group (WGII) will be published in Brussels on 6 April. Based on the work of hundreds of scientists, the report on "impacts, adaptation and vulnerability" is an appraisal of the effects of climate change. It follows a report from the first working group, published in February, which removed any doubts that climate change is caused by human activity. The third working group report, to be published on 4 May, looks at measures that might be taken to mitigate climate change and their economic effects.

A synthesis report from the three working parties will be published on 16 November, ahead of the next round of climate change negotiations. Together these reports make up the IPCC’s fourth assessment.

The IPCC reports are regarded as the most authoritative source of information on climate change. The first assessment, published in 1990, helped to put global warming on the UN’s agenda. Two subsequent assessments have pin-pointed the risks with increasing precision. While the 2001 report estimated the average global rise in temperature over this century to be between 1.4°C and 5.8°C, this year’s report gives a best estimate of between 1.8°C and 4.0°C, with the possibility of increases up to 6.4°C. Some have argued these figures are too broad to help policymakers. But Jason Anderson, head of the climate change programme at the Institute for European Environment Policy, disagrees. It is better to be "right within a range than wrong with great specificity", he says. He emphasises that the reports are very cautious, terms such as ‘likely’ and ‘very likely’ are not thrown around, but used and defined carefully.

Next week’s WGII report will be no exception. It will set out a range of scenarios and look at the impact of a warming world on water supplies, farming and the natural environment. Under one scenario, a rise in temperature above 3°C could mean water shortages for between 1.1 and 3.2 billion people, resulting in falling crop yields throughout the world. A rise above 4°C could mean the loss of 45% of tree species in the Amazon rainforest. The developing world will be hardest hit.

As underlined by the Stern Review, a British study on the economics of climate change published last October, the disadvantages of geography mean that Asian and African countries will pay the highest costs and see the least benefits from climate change. The poorest countries will suffer most because of their dependence on agriculture, the bit of the economy that is most sensitive to climate change.

The IPCC reports emphasise that choosing a low emissions scenario could prevent the worst effects. But a certain level of warming is already under way. That is why the IPCC looks at adaptation, climate jargon for preparing for warming that cannot be avoided. Stephan Singer at WWF, the environmental group, says that adaptation should not be seen as a new policy, because it covers issues governments should be thinking about anyway, such as bio-diversity in agriculture, avoiding building in flood prone areas and clearing shanty towns in developing countries. "Adaptation is good practice, not rocket science," he says. But he emphasises the limits of adaptation: "We will never be able to replace mitigation [cutting emissions], because some ecosystems, the Arctic for example, just cannot adapt." Cutting emissions, the subject of the third part of the IPCC’s 4th assessment, is something EU leaders have already signed up to. The picture painted by the IPCC’s 2007 reports should sharpen their resolve.

• Jennifer Rankin is a freelance journalist based in Brussels.

Experts and policymakers will gather in Brussels next week to discuss a world that is two or three degrees warmer, in which millions will be without water, tens of millions displaced by floods, tropical diseases could multiply and some species will die out.