"The impacts of a changing climate are beginning to emerge," said the report, titled Stronger Evidence But New Challenges: Climate Change Science 2001-2005, adding that evidence of warming was becoming easier to observe.

"High temperature extremes, such as the August 2003 heatwave in central Europe that had severe impacts on human health, are becoming more common."

The report said its findings were based on new research since the UN Intergovernmental Panel on Climate Change projections in 2001, which predicted temperature rises of between 1.4 and 5.8 degrees Celsius by the end of the century.

The report downgraded the long-term cooling affect of aerosol particles in the atmosphere, and found melting snow and ice would cut the reflectivity of the earth's surface and add to rising temperatures.

"The most dramatic example of this effect will likely occur in the Arctic Ocean, which is now projected to become almost totally ice-free in summer later this century," the report said.

"Retreating ice and snow expose darker underlying land and ocean surfaces, leading to enhanced absorption of sunlight and further warming."

BLOWING HOT AND COLD IN ANTARCTICA

At the other end of the globe, the report said the Antarctic peninsula was warming strongly, leading to a rapid loss of ice shelves along the coast and speeding up movement of glaciers.

By contrast, in the interior of Antarctica there had been an increase in snowfall, leading to an accumulation of ice over the centre of the continent.

The report said the concentration of carbon dioxide in the atmosphere continued to increase, while the upper layers of the world's oceans were warming.

Warmer sea surface temperatures lead to more moisture and heat in the atmosphere, fuelling storms. But a warmer world can also lead to more intense droughts, threatening the livelihoods of millions around the globe.

The report said climate change might be making hurricanes and typhoons more destructive, though not necessarily more numerous.

Many scientists blame global warming on the burning of fossil fuels, which release large amounts of carbon dioxide. Agriculture also releases huge amounts of methane, another greenhouse gas.

Australia's Environment Minister Ian Campbell released the report on Tuesday while announcing Australia remained on target to meet its greenhouse gas emissions targets of 108 percent of 1990 emissions by 2012 under the UN's Kyoto Protocol.

Australia and the United States have not ratified the Kyoto Protocol, which obliges about 40 nations to cut emissions by at least 5.2 percent below 1990 levels by 2008-12, saying it is unfair because developing nations are exempt.

Australia and the United States are pushing for voluntary measures to cut emissions, and stronger cooperation on clean technology, under a six-nation climate initiative including South Korea, Japan, China and India.