The latest UN report on climate change says mankind is "very likely" to be the cause of global warming and predicts a rise in temperature of between 1.8-4C (3.2-7.2F) by 2100.
The report says is it 90% certain global warming is man-made
Here is a selection of reactions to the report from around the world.
FRENCH PRESIDENT JACQUES CHIRAC
Soon will come a day when climate change escapes all control. We are on the verge of the irreversible.
Faced with this emergency, the time is not for half-measures. The time is for a revolution: a revolution of our awareness, a revolution of the economy, a revolution of political action.
ACHIM STEINER, UN ENVIRONMENT
The new report gives us a stark warning that the potential impact will be more dramatic, faster and more drastic in terms of consequences than previously thought.
This will change in some parts of the world the fundamental way in which we live.
STAVROS DIMAS, EUROPEAN ENVIRONMENT COMMISSIONER
I am deeply concerned at the accelerating pace and the increasing extent of climate change.
It is now more urgent than ever that the international community gets down to serious negotiations on a comprehensive new worldwide agreement to stop global warming.
GEORGIY GOLITSYN, CHAIR OF RUSSIAN ACADEMY OF SCIENCES CLIMATE COUNCIL
The main thing is that [the report] repeats and reiterates the influence of human activity on climate change, which is already happening.
This Russian winter hasn't been a winter at all because of climate change.
AINUN NISHAT, BANGLADESH REPRESENTATIVE OF INTERNATIONAL UNION FOR CONSERVATION OF NATURE
Bangladesh will be one of the countries that would be the most seriously affected by global warming and sea rise.
The impacts on Bangladesh would include increased levels of drought, flooding and storms, especially in coastal belts, salinity and loss of land.
Millions of Bangladeshis will lose their land and homes, adding to the South Asian country's plight of poverty and overcrowding.
HANS JOACHIM SCHELLNHUBER, POTSDAM INSTITUTE FOR CLIMATE IMPACT RESEARCH, GERMANY
With this report, any last doubts should be dispelled that humans are "over-turning the climate screw".
Hence, we have a responsibility to correct this dangerous development by drastically reducing greenhouse gas emissions.
SHARON HAYS, WHITE HOUSE OFFICE OF SCIENCE AND TECHNOLOGY POLICY, US
This report is a comprehensive and accurate reflection of the current state of climate change science.
(President George W. Bush) has put in place a comprehensive set of policies to address what he has called the "serious challenge" of climate change... the current set of policies are working.
STEPHANIE TUNMORE, GREENPEACE INTERNATIONAL
There is a clear message to governments here, and the window for action is narrowing fast.
If the last IPCC report was a wake-up call, this one is a screaming siren.
DAVID MILIBAND, UK ENVIRONMENT SECRETARY
What's now urgently needed is the international political commitment to take action to avoid dangerous climate change.
This has been absent so far. If we are to succeed, we will require the engagement not just of environmental ministers but heads of state, prime ministers and finance ministers.
This first report by the IPCC, and others to follow later this year, can provide a strong evidence base needed to move the prospects of agreement closer.
ANDREW WALKER, AUSTRALIAN GRAINS BROKER, FOX COMMODITIES
Plant breeders and the like have developed varieties of wheat, barley, sorghum, cotton, soybeans, you name it, that are using less and less water. Farmers are confident that things will evolve over time.
OK maybe we will have hotter temperatures and less rainfall in 100 years' time, but if you look at the variety of crops they're growing today versus 100 years ago, they've adapted crops to suit today's conditions.
I dare say they'll adapt them to suit conditions in 100 years' time.
JAN KOWALZIG, FRIENDS OF THE EARTH
The IPCC report scientifically confirms the extent of this man-made crisis already hitting people around the world and makes bleak predictions for the future.
We can no longer afford to ignore growing and compelling warnings from the world's leading experts.