Gordon Brown and his fellow G8 leaders are set to enter crunch talks on plans to halt global warming. On Wednesday, the G8 reached an agreement - hailed as "historic" by the Prime Minister - to seek to limit average global temperature increases to 2C by cutting their greenhouse gas emissions by 80 per cent by 2050. But the group of major industrialised powers now faces a tough challenge to secure agreement from emerging economies to accept caps on their own fast-increasing carbon use. China and India believe that the lion's share of any self-restraint must be shown by the western nations which have contributed most to global warming by their use of fossil fuels since the industrial revolution. Earlier this week, Indian prime minister Manmohan Singh said the West bore a "historical responsibility" for climate change, though negotiators at the G8 summit in L'Aquila, Italy, suggested that Delhi may be coming round to the need for agreement. China and India form part of the "plus five" group of emerging economies - also including Mexico, Brazil and South Africa - which will join the G8 nations for talks on climate change. These will be followed by a summit of the Major Economies Forum on the climate, chaired by US President Barack Obama and comprising these 13 states plus other major CO2 emitters like Australia, Indonesia and South Korea. Mr Brown has also secured strong support from the G8 in Britain's row with Iran over a detained embassy worker. A communique agreed over dinner at the end of the first day of the summit said: "G8 countries continue to be seriously concerned about recent events in Iran. "Interference with the media, unjustified detentions of journalists and recent arrests of foreign nationals are unacceptable. Embassies in Iran must be permitted to exercise their functions effectively under the Vienna Convention without arbitrary restrictions on or intimidation of their staff."