This is one of four proposals by the American university's Belfer Center for Science and International Affairs to negotiators who meet for UN climate talks next week in Poland.

The current climate pact, the Kyoto Protocol, expires in 2012 and governments are scrambling to agree a new treaty by the end of next year.

"The new agreement should be scientifically sound, economically rational and politically pragmatic," Professor Robert Stavins of the Harvard Project on International Climate Agreements said.

The Harvard report calls on rich nations to lead in cutting emissions, while developing countries can "maintain their business-as-usual emissions in the first decades, but over the longer term agree to binding targets that ultimately reduce emissions below business as usual."

U.N. scientists have warned global warming caused by high atmospheric levels of greenhouse gases like carbon dioxide will lead to rising seas, big storms, mass heatwaves and droughts.

"The agreement should be cost-effective and consistent with the recommendations of the Intergovernmental Panel on Climate Change," Stavins said, referring to the Nobel Peace Prize-winning scientific body.

Observers hope a new pact will include the US, which did not ratify the original agreement, and commit developing nations like China and India to binding emissions targets.

"We need an agreement that can be ratified in the US Senate and provide increasingly meaningful roles for developing countries. We see those as essential ingredients," Stavins said.

Last week President-elect Barack Obama said the U.S. would "engage vigorously" in climate change talks when he takes office next year.

Obama wants to reduce US carbon emissions to their 1990 levels by 2020 and cut them by an additional 80 percent by 2050.

The Harvard report proposes introducing national carbon taxes, linking emissions trading schemes or pursuing a series of simpler, possibly bilateral agreements that separately address the different gases and their sources as the other ways to fight warming.

"Countries will only participate in an international agreement if they believe they received a fair deal," the initiative said in a statement.

But the line dividing rich and poor nations set out in Kyoto may need to be redrawn, as the global economic landscape has altered in the past 10 years.

"If you look at the non-Annex I countries, 50 of them have higher per-capita income than the poorest Annex I countries," Stavins told Reuters.

The report said other key components of a new deal should promote clean energy technology transfer between rich and poor nations, reform Kyoto's emissions trading schemes and combat deforestation, something the original treaty failed to address.

It emphasized that any new deal must be compatible with global trade policy to prevent potential trade wars.

"Global efforts to address climate change may be on a 'collision course' with the World Trade Organization, as nations that have agreed to put a price on carbon look for ways to keep their companies competitive globally," the report said.

Citing the WTO as an example, the report suggests an independent international institution be set up to survey and review the policies, actions and outcomes of participating countries' climate change policies.

The report combines the work of 28 research teams from around the world, including China, India, the US and Europe.