More heat waves and periods of heavy rainfall are also very likely to occur, tropical cyclones are predicted to become more intense and a dramatic decrease in the polar ice caps is expected as air and ocean temperatures keep rising.

In the worst-case scenario, nearly one third of all of plant and animal species could be at risk of extinction.

The report also finds that industry, agriculture and infrastructure can become far more energy-efficient; water can be more effectively conserved; and used and countries can become less dependent on fossil fuels and other non-renewable sources of energy.

Slowing and even reversing the effects of climate change "is the defining challenge of our age," said Mr. Ban after launching the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC), which this year shares the Nobel Peace Prize for its work.

"We can transform a necessity into virtue," he said. "We can pursue new and improved ways to produce, consume and discard. We can promote environmentally friendly industries that spur development and job creation even as they reduce emissions. We can usher in a new era of global partnership, one that helps lift all boats on the rising tide of climate-friendly development."

The report, released in Valencia, Spain, is the synthesis of three IPCC reports issued earlier this year that examined the scientific basis of climate change, the impact it is having and ways to mitigate and adapt to the phenomenon. (Watch the IPCC press conference)

It is expected to form the basis of discussions in Bali next month, when world leaders gather under the auspices of the UN to try to agree to a successor pact to the Kyoto Protocol on greenhouse gas emissions, which is due to expire by 2012.