Even the most stalwart greenhouse skeptics no longer deny the planet's surface is heating up.

The last serious cause for suspicion dissipated in 2004 when British scientists debunked the notion that rising temperatures are a false impression, created by the growing sprawl of urbanization.

Which is not to say the urban-heat-island effect isn't real. It's well-known that cities, with their concrete and asphalt, are hotter than rural areas. Many of the stations that gather temperatures are near cities.

American researchers examined the possibility that urban heat was masquerading as global warming in 1997, by comparing data from all over the globe with measurements made only in rural areas. The warming was the same.

Last year, David Parker, of Britain's Hadley Centre for Climate Prediction and Research, settled the question emphatically by comparing measurements taken on calm and windy nights.

If urbanization was making the planet look hotter than it really is, the effect should be more pronounced when there's no wind to dissipate the heat from sweltering cities. But rates of warming were the same whether the wind was blowing or not.