"We live in an era of man-made climate change," said Vicente Barros, co-chair of working group II. "In many cases, we are not prepared for the climate-related risks that we already face. Investments in better preparation can pay dividends both for the present and for the future."

Although there are opportunities to respond, the risks will be difficult to manage with high levels of warming, according to the report. In that case, says WGII co-chair Chris Field, "even serious, sustained investments in adaptation will face limits".

What's more, the summary for policymakers says that "the precise levels of climate change sufficient to trigger tipping points remain uncertain, but the risk associated with crossing multiple tipping points in the Earth system or in interlinked human and natural systems increases with rising temperature".

The report details climate change impacts so far, such as changes in the quantity and quality of water resources, shifts in the range of animal and plant species, and altered crop yields, as well as the adaptation measures adopted to date.

"Climate-change adaptation is not an exotic agenda that has never been tried," said Chris Field, co-chair of working group II. "Governments, firms and communities around the world are building experience with adaptation. This experience forms a starting point for bolder, more ambitious adaptations that will be important as climate and society continue to change."

Facing the risk

For the first time the WGII report includes a focus on risk, which it says supports decision-making in the context of climate change. "People and societies may perceive or rank risks and potential benefits differently, given diverse values and goals," states its summary for policymakers.

Many of the key risks are particular challenges for the least developed countries and vulnerable communities, given their limited ability to cope, concludes the document.

"Understanding that climate change is a challenge in managing risk opens a wide range of opportunities for integrating adaptation with economic and social development, and with initiatives to limit future warming," said Field. "We definitely face challenges, but understanding those challenges and tackling them creatively can make climate-change adaptation an important way to help build a more vibrant world in the near-term and beyond."

The economic impacts of climate change are hard to pin down. For an additional warming of 2°C, global annual economic losses have been estimated to be from 0.2 to 2% of income, according to the report, but are more likely than not to be larger than this range. And individual countries would see big differences in the losses sustained. The incremental economic impact of emitting carbon dioxide may lie between a few dollars and several hundred dollars per tonne of carbon, depending on the amount of damage and discount rate assumed.

Regional variation

WGII has defined key risks, along with potential adaptation measures, for each region. For Africa these are stress on water resources, reduced crop productivity and climate-related changes in vector- and water-borne diseases. Europe, meanwhile, could see increased flooding in river basins and coasts, less water availability and more extreme heat events. In Asia the key risks are likely to be more riverine, coastal and urban flooding, greater risk of heat-related mortality, and more drought-related water and food shortage. Australasia could see problems for coral reefs, more frequent and intense flood damage, and increasing risks to coastal infrastructure and low-lying ecosystems.

North America is likely to suffer increased problems with wildfires, heat-related human mortality, and urban floods in riverine and coastal areas. Central and South America could see increased risks to human health, problems with water availability in some regions, and flooding and landslides due to extreme precipitation in others, and decreased food production and quality. At the poles there could be problems for ecosystems, risks for the health and wellbeing of Arctic residents, and challenges for northern communities. Small islands are likely to see threats to low-lying coastal areas as well as loss of livelihoods, infrastructure, ecosystem services and economic stability. And the oceans could well experience a shift in fish and invertebrate species, reduced biodiversity, lower fisheries abundance, less coastal protection by coral reefs, and coastal inundation and habitat loss.

More publications

This fifth assessment WGII report relies on more published literature than its fourth assessment predecessor, which was released in 2007. The number of scientific publications covering climate-change impacts, adaptation and vulnerability more than doubled from 2005 to 2010, with an especially rapid rise in papers on adaptation, according to WGII.

A total of 309 coordinating lead authors, lead authors and review editors, from 70 countries, put together this fifth assessment report, with help from 436 contributing authors and 1729 expert and government reviewers.

• The IPCC's working group III report, on climate mitigation, is due to be released on 13 April.