Could smog protect against global warming? (it's a Nobel concept!)

NAIROBI, Kenya - If the sun warms the Earth too dangerously, the time may come to draw the shade.

The ''shade'' would be a layer of pollution deliberately spewed into the atmosphere to help cool the planet. This over-the-top idea comes from prominent scientists, among them a Nobel laureate. The reaction here at the U.N. conference on climate change is a mix of caution, curiosity and some resignation to such ''massive and drastic'' operations, as the chief U.N. climatologist describes them.

The Nobel Prize-winning scientist who first made the proposal is himself ''not enthusiastic about it.''

''It was meant to startle the policy makers,'' said Paul J. Crutzen, of Germany's Max Planck Institute for Chemistry. ''If they don't take action much more strongly than they have in the past, then in the end we have to do experiments like this.''

Serious people are taking Crutzen's idea seriously. This weekend, NASA's Ames Research Center in Moffett Field, Calif., hosts a closed-door, high-level workshop on the global haze proposal and other ''geoengineering'' ideas for fending off climate change.

In Nairobi, meanwhile, hundreds of delegates were wrapping up a two-week conference expected to only slowly advance efforts to rein in greenhouse gases blamed for much of the 1-degree rise in global temperatures in the past century.