Margaret Beckett is to chair the first UN security council discussion on the effect climate change could have on world security.
The foreign secretary is heading to New York to lead a debate among the 15 members of the council and other affected parties on the potential for conflict in the event of global warming.
Britain holds the rotating presidency of the security council and Ms Hewitt will talk to members about how issues such as drought, floods and increasing sea levels could have major implications around the world.
Security council members usually discuss conflicts and wars which have security implications around the world and this afternoon's debate signals a step away from these more traditional matters.
Some members, particularly China and Russia, have expressed concern about widening the council's remit to include global warming.
Ms Beckett gave an indication as to what her main debating points would be when she addressed the transatlantic business organisation BritishAmerican Business Inc yesterday.
"The implications of climate change for our security are more fundamental and more comprehensive than any single conflict," she told delegates.
"The resources available to us are already stretched and they’re under immense and growing strain and an unstable climate threatens to exacerbate all of these existing tensions."
Commenting on Britain's decision to pursue the climate change agenda at the security council, Dr Tobias Feakin, the head of homeland security capabilities at the Royal United Services Institute, called it a "large step in acknowledging that there are going to be quite serious security implications from our changing climate".
"I would certainly say climate change is climbing the political agenda," he told the Today programme.
"It is becoming increasingly prominent, but as a security issue it is a fairly unresearched area at present.
"I have to say that the UK is leading the way in this sense."
He added: "Probably one of the largest concerns, which will be discussed today, is mass migration as a consequence of climatic change within specific regions.
"If we take, for example, Bangladesh, it is predicted that just a 1.5-metre rise in sea level in that region could lead to around 16 per cent of the country becoming flooded. At present there are 20 million people in that country so by 2050 we are looking at more like 35 million."
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