Governments across the globe are being urged to act immediately before climate change wipes out species, increases hunger and leads to water shortages and floods.
The dire warnings are included in a new report by the Intergovernmental Panel on Climate Change.
In reaction to the IPCC report, experts in Canada are appealing to citizens to make small changes in their own lives and to pressure representatives to take action.
"Canadians are now worried that this is a serious problem that requires serious solutions," Jose Etcheverry, climate change analyst with the David Suzuki Foundation, told Â鶹ӰÊÓnet.
"The consequences directly depend on the action or the lack of action that we take. If we continue to be asleep at the button, the consequences will be much more serious."
"The key thing here is to demand our policy makers and decision makers take action on our behalf and on the individual level, we need to reexamine how we heat and cool our homes, where the electricity we use in our homes comes from and how do we transport ourselves," Etcheverry said on Friday.
Liberal leader Stephane Dion reacted to the document in a statement saying, "Canada must be ready for a carbon constrained future. Today's report makes it clear that human activity is changing our planet in a fundamental way."
"It is within our power to prevent the worst of the effects of climate change, and to adapt to the climate change that will inevitably occur. But we can only do that if as a country we are ready to take serious steps immediately," Dion said on Friday.
Poor countries most at risk
After an all night session which saw key sections deleted from the draft report and scientists confronting government negotiators whom they suspected were watering down their findings, agreement was finally reached on the wording of the report.
"It has been a complex exercise," said Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change.
In a review of the report's findings, Dr Martin Parry, co-chairman of IPCC Working Group II, said there are four key areas of the world that are the most susceptible to climate change.
"The arctic, where temperatures are rising fast and ice is melting; sub-Saharan Africa, where dry areas are forecast to get dryer; small islands, because of their inherent lack of capacity to adapt and Asian mega-deltas, where billions of people will be at increased risk of flooding," he explained, reports the BBC.
Pachauri told reporters Friday that "the poorest of the poor in the world" will be affected the worst if change doesn't occur.
He said it will include "poor people even in prosperous societies."
"This does become a global responsibility in my view," he said.
The report predicts the following:
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Up to 30 per cent of species will face extinction if global temperatures rise 1.5 to 2.5 degrees Celsius above the average recorded in the 1980s and '90s.
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Areas currently suffering from a shortage of rain will become even drier, increasing the risks of hunger and disease.
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In Africa, climate change could create a drastic fall in crop yields, meaning hunger for millions.
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The world will also face heightened threats of flooding, severe storms and coastline erosion that could affect billions.
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Climate change could also thaw Himalayan glaciers and usher in heat waves for Europe and North America.
Heated debate
The IPCC is the world's top authority on climate change and is made up of 2,500 scientists and representatives from more than 100 nations.
The report is the second in a series of four and was approved after a marathon session that included angry exchanges between diplomats and scientists.
The report will be used to help guide UN policy on issues that include extending the Kyoto Protocol -- the main plan used to cap greenhouse gas emissions -- past 2012.
"This further underlines both how urgent it is to reach global agreement on reducing greenhouse gas emissions and how important it is for us all to adapt to the climate change that is already under way," European Environment Commissioner Stavros Dimas told Reuters.
Several scientists had objected to the editing of the final draft by government negotiators but eventually agreed.
However, many say they will never contribute to the process again.
"The authors lost," said one scientist. "A lot of authors are not going to engage in the IPCC process anymore. I have had it with them,'' he said on condition of anonymity.
Many were angered after delegates removed parts of a key chart that highlighted the detrimental effects that climate change will have with every single degree Celsius increase.
The U.S., China and Saudi Arabia raised the most objections to the phrasing, attempting to tone down some of the more extreme projections, confirmed a reporter with The Associated Press.
China, second only to the U.S. in greenhouse gas emissions, fought to delete a reference to "very high confidence" that climate change was already influencing "many natural systems, on all continents and in some oceans."
The report follows one by the IPCC in January that said human greenhouse gas emissions, mostly from burning fossil fuels, are the most likely cause of global warming.
With files from Â鶹ӰÊÓnet and from The Associated Press