Scientists and representatives of 195 governments meeting in South Korea have approved a report on the impacts of a rise of 1.5C above pre-industrial levels and the action needed to limit global warming to that level.
Ahead of its publication, Neil Thorns, director of advocacy at Catholic international development charity (Cafod), said: "This report proves that keeping global temperatures to 1.5 degrees is a necessity not an ambition.
"Faced with such information we cannot leave poor communities standing on the frontline of this potential storm, we must act urgently.
"Pope Francis has challenged politicians to ensure that their actions leave a legacy that does 'care for our common home' in the long-term and this report is yet another wake up call for them."
The finalised report is due to be published on Monday and will sound a warning about the speed and scale of measures required to keep temperature rises to a level beyond which many vulnerable countries say their survival is at risk.
It will prompt new calls for dramatic and urgent steps to cut greenhouse gas emissions to zero by 2050.
That would mean an end to burning fossil fuels to generate power, the replacement of petrol and diesel cars with electric vehicles or other clean alternatives and no more gas boilers to heat homes, in just a few decades.
Scientists have also warned that protecting and restoring forests will be key to cutting carbon and drawing down excess emissions from the atmosphere.
The world is already experiencing around 1C of global warming, and events such as floods, storms and this summer's heatwave have become increasingly likely as a result of climate change.
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