Tim Flannery, named the 2007 Australian of the Year for his work in alerting the public to the dangers of global warming, said the issue was the greatest challenge facing humanity in the 21st century.

Flannery said predictions in a 2001 UN report, warning the atmosphere was likely to warm by 1.4 to 5.8 degrees Celsius (2.5-10.4 Fahrenheit) from 1990 to 2100 now appeared conservative.

"In the six years since then, we've collected enough data to (check) whether those projections are valid or not," he said.

"It turns out they're not valid, but in the most horrible way -- because for the key performance indicators about climate, change is occurring far in advance of the worst-case scenario," he said.

"Carbon dioxide's increasing more rapidly, sea levels are rising more rapidly (and) the Arctic ice cap is melting away more quickly than were projected in 2001."

Flannery said the world needed an international organisation similar to the United Nations dedicated solely to climate change.

"The 21st century is going to be about environmental limits," he said.

"There's six billion of us on the planet, there will soon be nine billion, the atmosphere is tiny as a pollution receptacle, clearly that's going to be where the action is.

"But we haven't yet built the structures, the new version of the UN that helps us deal with the global pollution crisis as a species."

Flannery said nations needed to "de-carbonise" their economies by 2050, increasing reliance on geo-thermal, nuclear and renewable energy.

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