Here's one plus from the global economic recession: Carbon dioxide pollution last year dropped for the first time in a decade.
But it didn't last and it wasn't as big a drop as expected.
Burning fossil fuels to power factories, cars and airplanes spews out greenhouse gases that warm the world. But during the economic downturn, some factories shut down and people didn't drive or fly as much. The helped drop emissions about 1.3 percent from 2008 to 2009, according to a study published Sunday in the journal Nature Geoscience.
There's been a close link between gross domestic product and pollution in recent decades, said study lead author Pierre Friedlingstein of the University of Exeter in England. "The good part of the crisis is that it reduces emissions."
In the United States, the Energy Department said that emissions dropped 7 percent in 2009 because of three equal factors: the slowing economy, slightly better energy efficiency and cleaner energy.
Worldwide, it was mostly a matter of the economy, Friedlingstein said. In 2009, the world spewed nearly 34 billion tons (about 31 billion metric tons) of carbon dioxide. That's a drop of 453 million tons from the previous year — what the U.S. emits in about 26 days.
The last time carbon dioxide pollution dropped worldwide was in 1999 and this was the biggest decrease since 1992, according to records by the Energy Department's Oak Ridge National Lab. Despite last year's improvement, worldwide carbon emissions have increased by 25 percent since the year 2000.
Carbon pollution is probably already rising this year, the study authors said, and likely to set yet a record in 2010.
The same scientists last year had forecast almost a 3 percent drop in emissions for 2009 based on GDP projections from the International Monetary Fund. But the economy improved more than expected and developing countries kept increasing the amount of carbon dioxide they produced, Friedlingstein said.
Developing nations aren't using energy as efficiently and they weren't as affected by the recession as the west, he said.
China's carbon dioxide pollution jumped 8 percent from 2008 to 2009. India's went up about 6 percent, according to the study.
That's part of a dramatic shift in which countries are producing the most carbon dioxide. In 1990, the developed world produced 65 percent of the world's carbon dioxide, said study co-author Gregg Marland of the Oak Ridge National Lab. Now it is less than 43 percent as those countries have cut about 10 percent of their emissions while the developing world has more than doubled their overall emissions.
One bright note is that overall carbon dioxide emissions from the destruction of forests has slowed considerably, Friedlingstein said.
Despite that, it looks like the world cannot reach the goal set by international negotiations in Copenhagen last year of limiting global warming to a 3.6 degree (2 degree Celsius) temperature increase since industrialization, said University of Victoria climate scientist Andrew Weaver, who wasn't involved in the study. Through the first 10 months of the year, 2010 is tied for the hottest year in 131 years of record keeping, according to the National Climatic Data Center.
"We are letting global warming emissions get away from us," Weaver said. "You can't say the climate science community didn't say 'I told you so.'"