KEY POINTS:
The UN's Intergovernmental Panel on Climate Change on the risks of climate change:
Observed changes
"Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level."
Causes of change
"Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in ... greenhouse gas concentrations" from human activities.
Annual greenhouse gas emissions from human activities have risen by 70 per cent since 1970. Concentrations of carbon dioxide, the main greenhouse gas, far exceed the natural range over the last 650,000 years.
Projected climate changes
Temperatures are likely to rise by between 1.1C and 6.4C and sea levels by between 18cm and 59cm this century.
Africa, the Arctic, small islands and Asian mega-deltas are likely to be especially affected by climate change. Sea level rise "would continue for centuries" because of the momentum of warming even if greenhouse gas levels are stabilised.
"Warming could lead to some impacts that are abrupt or irreversible". About 20-30 per cent of species will be at increasing risk of extinction if future temperature rises exceed 1.5C-2.5C.
Five reasons for concern
* Risks to unique and threatened systems, such as polar or high mountain ecosystems, coral reefs and small islands.
* Risks of extreme weather events, such as floods, droughts and heatwaves.
* Distribution of impacts - the poor and the elderly are likely to be hit hardest, and countries near the equator, mostly the poor in Africa and Asia, generally face greater risks such as of desertification or floods.
* Overall impacts - there is evidence since 2001 that any benefits of warming would be at lower temperatures than previously forecast and that damages from larger temperature rises would be bigger.
* Risks or "large-scale singularities", such as rising sea levels over centuries; contributions to sea level rise from Antarctica and Greenland could be larger than projected by ice sheet models.
