"We live in an era of man-made climate change," said Vicente Barros, co-chair of the group which produced the report. "In many cases, we are not prepared for the climate-related risks that we already face."
The impact on our food sources and weather could be huge, according to the report. Any benefits from warmer temperatures, like growing crops like grapes further north, will be far outweighed by the negatives , with wheat and maize particularly affected, the scientists argue.
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And it is the world's poorest people who will be hit hardest, they wrote.
The impact of climate change is being felt "from the tropics to the poles, from small islands to large continents, and from the wealthiest countries to the poorest," they wrote. The risk of extreme weather events will also rise with temperatures, the report warned.
These events can have a devastating impact on economies around the world, particularly those which are most densely populated and have the worst infrastructure.
However, the economic impact of climate change is difficult to forecast, and estimates vary widely. A temperature increase of around 2 degrees Celsius would lead to global income losses of between 0.2 and 2.0 percent, according to the report's median estimates – warning that any losses are more likely to be greater than this range.
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Previous warnings from the IPCC have not been followed by substantial actions on climate change. Consumption of fossil fuels, a key factor in global warming, dipped slightly during the global credit crisis, but has since recovered.
The science behind climate change has been contentious, with some scientists arguing that climate change is part of a natural process rather than man-made, and others that it will not necessarily be negative for the world.
The IPCC report was put together by just over 300 coordinating lead authors, lead authors, and review editors, representing 70 countries around the world, and 1,729 expert and government reviewers.
There was some room for optimism about how governments are starting to adapt to climate change in the report. Its authors called for greater co-operation and co-ordination between governments on the issue.
Christopher Field, co-chair of the working group and founding director of the Carnegie Institution's Department of Global Ecology in California, warned: "we're not talking about hypothetical events."