Climate change could have far-reaching and "irreversible" consequences if more action is not taken to cut greenhouse gas emissions, a UN scientific panel warned in a report released Saturday.

UN chief Ban Ki-moon, right, and panel chairman Rajendra Pachauri hold the report in Valencia, Spain.
(Fernando Bustamante/Associated Press)

The Intergovernmental Panel on Climate Change (IPCC) said in its report that evidence of climate change is "unequivocal." 

It said the trend could lead to "abrupt" changes to the planet, cause human suffering and threaten some species with extinction.

"Slowing and reversing these threats is the defining challenge of our age,'' UN Secretary-General Ban Ki-moon said as he unveiled the report in Valencia, Spain.

The Summary for Policymakers and a longer version called the Synthesis Report were written from thousands of pages of data and computer models based on six years of research compiled by the IPCC.

The 23-page summary said climate systems unquestionably have already begun to change and that human activities since the start of the industrial age have contributed to the warming.

The evidence, it said, can be seen in the measured warming of air and ocean temperatures, widespread melting snow and ice, and rising sea levels.

Poor, elderly would suffer most

The panel, which won a Nobel peace prize earlier this year, said recent research has heightened concerns that the poor and the elderly would suffer most from climate change.

Scientists predict that 20 to 30 per cent of species could face an increased risk of extinction if the global temperature rises by even 1.5 to 2.5 degrees.
(Subhankar Banerjee/Associated Press)

It warned hunger and disease will be more common; droughts, floods and heat waves will afflict the world's poorest regions and more animal and plant species will vanish.

"Those who are most vulnerable are also the most at risk from this threat," Ban said.

"There is medium confidence that approximately 20 to 30 per cent of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5 to 2.5 degrees C (relative to the 1980-1999 average)," the summary concluded.

The panel, issuing its fourth and final report of the year, said carbon dioxide emissions blamed for global warming are rising faster than they were a decade ago.

Despite the dire warnings, the report also contains the message that there are "real and affordable ways to deal with climate change," Ban said.

He urged politicians meeting in Bali, Indonesia next month to use the research as a guideline in their environmental talks.

About 10,000 delegates will meet to discuss a proposed international pact on climate change to succeed the emissions-limiting Kyoto Protocol, which expires in 2012.