As the planet warms due to carbon dioxide emissions, the annual death rate is forecast to climb, with premature deaths in the United States from human-generated carbon dioxide expected to hit 1,000 a year when the global temperature has risen by 1.8 degrees F (1 degree C).

When the planet gets that hot, which could happen this century, the world annual death rate is estimated to rise to 21,600, Jacobson said on Friday in a telephone interview.

Earth has warmed about 1.4 degrees F (0.8 degrees C) in the last 150 years, with most of that gain in the last three decades. Jacobson said about 700 to 800 US annual deaths in the most recent years can be attributed to human-caused carbon emissions.

Greenhouse gas pollution has spurred the global warming that is result in a damaging rise in the sea level, droughts and possibly more severe storms this century. This is the first time a scientist has specifically linked one human-generated greenhouse gas to human mortality.

Carbon dioxide is one of several greenhouse gases blamed for climate change, but it is the one humans have the most ability to control through regulation of activities that burn fossil fuels like coal and oil. It is also emitted by natural processes.

IMPACT ON CALIFORNIA

Using a complex computer model and data on carbon emissions from the US Environmental Protection Agency, Jacobson found the impact was worse in places that are populous and polluted.

"Of the additional ... deaths per year due to ozone and particles ... about 30 percent of those occurred in California, which has 12 percent of the (US) population," he said, noting that California has six of the 10 most polluted US cities.

"So it was pretty clear ... that climate change was affecting Californians' health disproportionately to its population," Jacobson said.

What happens in California is important, since this populous state has long been a testing ground for US pollution regulation.

Jacobson's study, to be published in Geophysical Research Letters, was released soon after the US Environmental Protection Agency rejected a bid by California and 15 other states to let them set higher standards for carbon emissions from cars, trucks and SUVs than the federal government does.

Jacobson's research was not available before the EPA's decision on Dec. 19, but the EPA's rejection made points that Jacobson said are addressed by his study.

In turning down the states' request, EPA argued that California did not have a special circumstance warranting this change, that there were no studies isolating carbon dioxide's effects and none looking at health impacts.

"It's actually occurring right now, it's been occurring for the past 20 to 30 years," Jacobson said of the deaths related directly to human-generated carbon dioxide emissions.