A group of the world's top climate scientists called on the leaders of the world's major economies to adopt strong measures to address climate change, including a peak in global emissions before 2020.

In a letter addressed to Ministers and Heads of State attending this week's G8 summit and Major Economies Forum on Energy and Climate in Italy, the climate scientists, including several senior government climate science advisors, make specific requests for policy action and warn that failure to reduce emissions presents "unacceptable risks."

The scientists are calling for action from world leaders whose nations represent around 70% of global carbon abatement potential. Among other specific requests, the scientists underscore the importance of committing to a global emissions peak by 2020 and beginning significant reductions in harmful greenhouse gases well before 2020.

"This is a very important moment in the run up to the climate negotiations in Copenhagen in December, aimed at achieving a global agreement", said Michael Oppenheimer, Professor of Geosciences and International Affairs at Princeton University, one of the signatories of an open letter to Major Economy leaders published today. "Scientists worldwide are calling on the leaders of the major economies 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. These countries should make clear that they are prepared to seize the opportunity to promote low-carbon economic growth and prosperity at home and abroad."

The letter makes five specific requests of major economy leaders:

1. Recognise that present global warming of 0.8 degrees C above pre-industrial levels is already having a significant impact, and that warming exceeding 2 degrees C predicted for later this century would create great risks and have irreversible consequences

2. Commit to peak global greenhouse gas emissions by no later than 2020 and reduce them by at least 50% relative to 1990 levels by 2050

3. For developed countries, commit to emissions reductions of at least 80% relative to 1990 by 2050 with appropriate intermediate targets set in time for Copenhagen

4. For developing countries, commit by Copenhagen to significant gains in energy efficiency, reductions in carbon intensity, and cuts in non-CO2 greenhouse gas emissions over the next two decades; this should be designed to support sustainable development and to lead to substantial reduction from business-as-usual emissions

5. Recognise that the impact of existing changes in climate are primarily due to past emissions by developed nations, and that unless the burden of poverty in developing nations is alleviated by significant financial support for mitigation, adaptation, and the reduction of deforestation, the ability of developing countries to pursue sustainable development is likely to diminish, to the economic and environmental detriment of all