World leaders must now respond to an "unequivocal" message from climate scientists and act with policies to cut greenhouse gas emissions, the United Nations secretary-general urged on Friday.

Introducing a major report from a high level UN panel of climate scientists, Ban Ki-moon said, "The heat is on. We must act."

The world's leading climate scientists, who have been meeting in all-night sessions this week in the Swedish capital, said there was no longer room for doubt that climate change was occurring, and the dominant cause has been human actions in pouring greenhouse gases into the atmosphere.

In their starkest warning yet, following nearly seven years of new research on the climate, the Intergovernmental Panel on Climate Change (IPCC) said it was "unequivocal" and that even if the world begins to moderate greenhouse gas emissions, warming is likely to cross the critical threshold of 2C by the end of this century. That would have serious consequences, including sea level rises, heatwaves and changes to rainfall meaning dry regions get less and already wet areas receive more.

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