L'Aquila, Italy  - A group of top international climate scientists on Monday urged leaders of the world's major economies set to attend a Group of Eight (G8) summit later this week, to take "strong measures" against harmful climate change.

The scientists outlined their concerns in a letter containing five steps they hoped leaders of the G8 - the US, Japan, Germany, France, Britain, Italy, Canada and Russia - would adopt at their meeting in L'Aquila, Italy, scheduled to begin Wednesday.

In particular, the scientists appealed for a commitment from the G8 to peak global greenhouse emissions by no later than the year 2020 and reduce them by at least 50 per cent relative to 1990 levels by 2050.

Major economies need to "send a signal to rest of the world that those countries with the highest emissions, those that are also in the best position to make the greatest contributions to reducing the risk, are ready to combat the threat posed by climate change," said one of the letter's signatories, Michael Oppenheimer, a Geosciences and International Affairs professor at Princeton University.

The pace and scale of emission cuts, remain major sticking points dividing G8 nations ahead of the L'Aquila summit and United Nations climate talks scheduled to be held in Copenhagen in December.

European Union members of the G8 have largely endorsed a commitment on peaking global emissions by 2020 and that world temperature change should be limited to 2 degrees Centigrade above pre-industrial levels.

But the US and Japan - the world's two biggest economies - have said that it would be wrong to agree on a mid-term target and overall temperature goal before the Copenhagen talks.

G8 members are also at odds over the question of how each one should define its national emissions reduction targets.

Meetings on the fringes of the G8 summit are also set to be fraught, with the Major Economies Forum (MEF) - the G8 plus Australia, Brazil, China, India, Indonesia, South Korea, Mexico and South Africa - also due to debate thorny issues of global warming.(dpa)