John Ashton is the UK's climate change ambassador who works to build international consensus on the issue.
He is described as a diplomat equally comfortable in the worlds of foreign policy and green politics.
Mr Ashton had a long career in the Foreign Office, including founding its environmental policy department, before moving outside government.
He believes that climate change must be treated as an immediate threat to national security and prosperity.
Before joining the diplomatic service in 1978, Mr Ashton studied natural sciences at Cambridge University.
He was seconded to the Hong Kong government in 1993, where he was an advisor to Chris Patten before the handover to China, where he has also served.
In 2004 he founded E3G, an independent not-for-profit organisation that works to make people and companies more environmentally friendly, by getting them to collaborate and by identifying clear goals.
As the foreign secretary's special representative on climate change his main role is to build a new international consensus on climate change.
Consensus and diplomacy were, he told the BBC News website last year, the only ways to tackle climate issues; unlike more traditional security concerns, the "hard power" option of solving a problem by force is not available.
"You cannot use military force to make everyone else on the planet reduce their carbon emissions. No weapon system can halt the advance of a hurricane bearing down on a city, or stem the rising sea, or stop the glaciers melting," he said.
Mr Ashton is a visiting professor at Imperial College, London, and a member of the Green College Centre for Environmental Policy and Understanding.
He is a steering committee member of Climate Care and serves on the Advisory Boards of the Climate Institute, Washington DC; the UK Tyndall Centre for Climate Change Research; the Bren School of Environmental Science and Management, University of California, Santa Barbara; and Climate Change Capital.