Pennsylvania's emissions of carbon dioxide from burning fossil fuels was 277 million tons in 2007, the third highest in the nation, but the commonwealth was also among 17 states where emissions of the greenhouse gas declined that year.

Nationwide emissions of carbon dioxide, the leading global warming pollutant, increased by 19 percent from 1990 through 2007, but the growth rate slowed in recent years, according to the 58-page report released today by PennEnvironment, a non-profit environmental organization.

The report said that the emissions reductions, though well short of the amount needed to reduce the worst effects of climate change, "could be a sign of a new trend, particularly if the United States adopts strong policies to move the nation toward a clean energy future."

To avoid the worst global warming impacts, scientists have targeted a 35 percent reduction in global warming emissions by 2020 and an 80 percent reduction by 2050.

The study said Texas remained the biggest emitter of carbon dioxide, totaling 675 million tons in 2007, followed by California's 400 million tons, Pennsylvania, Ohio's 270 million tons and Florida's 258 million tons.

But between 2000 and 2007, the latest year for which federal statistics are publicly available, the emissions of carbon dioxide increased at just one-fifth the rate they did in the 1990s.

And the study said estimates of emissions for 2008 declined by 2.8 percent, their lowest level since 2001, and are expected to decline further in 2009 due to the recession and the declining demand for fossil fuels.

Four states -- Connecticut, Delaware, Massachusetts and New York -- along with the District of Columbia reduced carbon dioxide emissions between 1990 and 2007. In Pennsylvania, carbon dioxide emissions increased by 5 percent over that 17 year time frame, but from 2004 through 2007 declined by 0.3 percent.

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