The 26-page report, released in the Spanish city of Valencia by the Nobel Peace Prize-winning Intergovernmental Climate Change, said warming of the climate system is "unequivocal" and governments must take action to avoid catastrophic consequences.

Climate change is "evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level," the report noted.

The report, which will be the first point of reference for political negotiators meeting next month for talks aimed at finding out a successor to the Kyoto Protocol, attributed global warming mainly to greenhouse gas concentrations caused by human activities.

Signed in 1997, the Kyoto Protocol requires 36 industrial countries to significantly reduce their carbon emissions. It expires in 2012.

"Global total annual greenhouse gas emissions from human activities have risen by 70 percent since 1970," the report said.

It also said governments have a wide range of tools including higher taxes on emissions, regulations, tradeable permits and more investment in research.

UN Secretary-General Ban Ki-moon welcomed the report, saying the potential impact of global warming is "so severe and so sweeping that only urgent, global action will do."