NAIROBI, Kenya (AP) -- Facing rising temperatures and flagging efforts to control greenhouse gases, thousands of delegates from around the world opened a UN conference Monday on next steps to ward off the worst effects of climate change.

Many at the two-week session will look for signs the United States might ease its stand against mandatory reductions in emissions that scientists blame for global warming. Few expect to see such a change, however, while the Bush administration is in power.

The delegates will get a closed-door preview, meanwhile, of the latest scientific findings on a warming world, to be published next year in a comprehensive UN assessment by the world's leading climate scientists. Among more recent results:

_World temperatures have risen to levels not seen in at least 12,000 years, propelled by rapid warming the past 30 years, U.S. climate scientists reported in September.

_NASA last month reported "dramatic" melting of Greenland's ice mass, at a rate of 41 cubic miles per year, far surpassing the gain of 14 cubic miles per year from snowfall.

_Britain's Hadley Center for Climate Prediction and Research forecast last month that extreme drought could eventually affect one-third of the planet if climate change is not reined in.

Scientists blame the past century's 1-degree-Fahrenheit rise in average global temperatures at least in part on the accumulation of carbon dioxide, methane and other heat-trapping greenhouse gases in the atmosphere — byproducts of power plants, automobiles and other fossil fuel-burning sources.

The 1997 Kyoto Protocol, an annex to the 1992 U.N. climate-change treaty, requires 35 industrialized countries to reduce those emissions by 5 percent below 1990 levels by 2012.

A UN report last week indicated many countries are struggling to meet their targets.

Industrialized nations' emissions declined in the 1990s after the collapse of the Soviet bloc and the shutdown of polluting factories and power plants in eastern Europe. But now those economies are rebounding, contributing to a 2.4 percent rise in emissions by all industrialized nations between 2000 and 2004, that report said.

Here in Nairobi, the Kyoto countries will continue talks on what kind of emissions targets and timetables should follow 2012. But many are waiting to see whether the biggest emitter, the United States, accounting for 21 percent of the world's greenhouse gases, will submit to a mandatory regime of cutbacks.