Leaders of the G8 leading industrial countries have agreed to try to limit global warming to just 2C (3.6F) above pre-industrial levels by 2050.

G8峰会主要工业国家的领导人达成共识，尽力在2050年以前将全球气候变暖控制在工业化以前的2C水平。

The summit, in the Italian city of L'Aquila, also set tough new targets for carbon emissions¹ considered necessary to achieve the goal.

Developed nations are to cut carbon emissions by 80% by 2050, to allow a global 50% reduction by the same date.

Analysts² say there is no indication（象征，迹象） of how the targets, or costs, will be met.

Developed nations have been criticised for ducking interim³（中间的，短暂的） goals, and difficult talks still lie ahead as negotiators try to firm up the ambitious（热望的，有抱负的） goals, correspondents say.

Also, the cut in carbon emissions is only a target and will need the co-operation of rapidly industrialising such as China and India.

BBC economics correspondent Andrew Walker adds that the baseline for the cuts could be later than 1990.

That could allow some countries more modest cuts, as emissions in most rose after that date.

UK Prime Minister Gordon Brown said he was confident non-G8 countries would back the commitments when climate change was discussed on Thursday.

Mr Brown said the G8 deal paved the way for a global agreement at the UN conference in Copenhagen in December.

"I hope tomorrow when we meet other countries we'll follow that through and this is a very significant development, the first time it's ever been done," he said.

Deadline

The summit agenda also includes the global economic downturn, food security, terrorism, North Korea and Iran.

President Nicolas Sarkozy of France said talks on Iran's nuclear programme would be given a chance until a G-20 summit in the US in September.

"If there is no progress by then, we will have to take decisions," he told reporters on Wednesday.

Iran has ignored UN calls to halt uranium enrichment（铀浓缩）, but says its nuclear programme is for peaceful purposes.

US President Barack Obama announced he would call a summit on nuclear security in Washington next March.

The G8 - Canada, France, Germany, Italy, Japan, Russia, UK and the US - are joined at the summit by leaders or representatives from the G5 group of emerging economies - Brazil, China, India, Mexico and South Africa.

Chinese president Hu Jintao flew back to Beijing amid continuing unrest in the western region of Xinjiang.

On the global economy, an official statement noted⁴ "some signs of stabilisation" but that the outlook remained uncertain, with "significant risks".

"We will take, individually and collectively, the necessary steps to return the global economy to a strong, stable and sustainable growth path," the statement said.

Mr Brown said G8 leaders recognised that the path out of recession was not yet secure, citing the recent rise in oil prices to $75 a barrel and fears of rising unemployment.

Earthquake zone

The area where the three-day summit is being held is still suffering aftershocks from the April quake and an evacuation（撤离，疏散） plan is in place in case a serious tremor⁵（震动，颤动） should hit.

African leaders will join the summit on Friday to push for a new initiative to fund farming in the developing world and tackle（处理，抓住） global hunger.

Italian Prime Minister Silvio Berlusconi moved the summit from Sardinia to L'Aquila to show solidarity⁶ with the victims of April's earthquake.

He took Mrs Merkel on a tour of Onna, a village almost flattened⁷ by the quake, and later Mr Obama was given a tour of L'Aquila to survey the damage.

On Wednesday, dozens of protesters occupied four coal power plants in different regions of Italy, demanding tougher measures in fighting climate change, Greenpeace said.

In Rome on Tuesday police said they had arrested 36 people after masked protesters blocked roads, threw objects and set fire to tyres.

The BBC's Bridget Kendall in L'Aquila says the big question hovering⁸（悬停） over the summit is whether the whole concept of G8 has been outdated⁹ and if a bigger gathering¹⁰ - a G20 - is needed to tackle today's problems.