The guarantee will go to the Innovative Finance Facility for Climate in Asia and the Pacific (IFCAP), a leveraged guarantee mechanism for climate finance which was announced in May by the Asian Development Bank.
Britain said the guarantee could unlock $1.2 to $1.8 billion in climate financing and would help achieve the United Nation's Sustainable Development Goals.
Those goals - a global 'to do' list set out in 2015 - are a focal point for the UN General Assembly, taking place this week against a backdrop of geopolitical tension as Russia and China vie with the U.S. and Europe to win over developing countries.
British Foreign Secretary James Cleverly will make the guarantee announcement at the assembly in New York. He will also announce further funding and guarantees worth 180 million pounds to support education through the International Finance Facility for Education.
