Others disagree, contending that natural factors, such as an increase in cloud cover, are at play.

WSJ: In Study, Past Decade Ranks Among Hottest

Many students of climate change argue that, although the artificial release of greenhouse gases such as carbon dioxide works to raise the global temperature, particulate pollution should, by promoting cloud cover and thus reflecting solar energy back into space, have a compensating cooling effect.

ECONOMIST: Weather and pollution

His (as yet unpublished) research confirms, he says, that the variations in cloud cover seen by satellites match those in cosmic-ray flux better than anything else, such as the sun's total brightness.

ECONOMIST: Global warming: In flux | The