Global leaders attending the G8 have agreed to cut their carbon emissions by 80 percent by 2050 and to limits on increases in world temperatures in the future, ADN-Kronos news agency reported.
According to the draft document released in advance to Adnkronos, the accord limits "the global increase in the average temperature to two degrees celsius in relation to preindustrial levels".
The same document reaffirmed a desire for all countries to reduce their global emissions by at least 50 percent by 2050, with even higher emissions from G8 countries.
British prime minister Gordon Brown said the G8 had agreed on the tough new carbon emission cuts and would try to prevent global average temperatures rising more than 2C above pre-industrial levels.
The Group of Eight - United States, Germany, Japan, France, Britain, Italy, Canada and Russia - began their summit discussing the economic crisis, after what one analyst called a "reality check" in recent weeks on the prospects for rapid recovery.
The leaders of the major industrial powers said there were signs of stabilisation in the world economy but warned that "significant risks remain".
The statement came as the International Monetary Fund said the world economy was beginning to emerge from recession.
The G8 summit is being held in the town of L'Aquila, Italy, where nearly 300 people died and 50,000 others were displaced in an earthquake in April.
US president Barack Obama was expected to make his mark on his first G8 summit by chairing Thursday's meeting in L'Aquila of the 17-nation major economies forum, whose members account for about 80 percent of global greenhouse gas emissions.
The summit agenda is also expected to include food security, North Korea and Iran.