Van Heusen

The April 3-8 talks are the first since environment ministers agreed a package last December in Mexico that put the U.N. negotiations back on track. Japan's nuclear crisis is likely to overshadow the 2011 sessions about low-carbon energies.

The December deal in the Mexican resort of Cancun included a Green Climate Fund to manage $100 billion a year in aid to poor nations by 2020 and to limit a rise in average world temperatures to below 2 deg C (3.6 F) over pre-industrial times.

"Governments need to maintain momentum at Bangkok by agreeing a clear work-plan for 2011," the U.N.'s climate chief Christiana Figueres said in a statement. The Bangkok talks will have to start working out details.

Cancun, for example, failed to make progress on tougher issues, such as disputes between rich and poor nations on how to extend or replace the existing Kyoto Protocol or strengthen the emission cuts pledged by rich nations.

"One of the key questions is whether the spirit of Cancun that allowed negotiators to make compromises and move forward still exists," said Jennifer Morgan, director of the climate and energy program at the World Resources Institute in Washington.