for National Geographic News
A broad scientific census says that Earth is already experiencing significant global warming. So how hot will it get, how soon, and to what effect?
Some climate scientists warn that the pace of global warming could be much more rapid than that predicted even a few years ago.
"Any time you get into projections, you get into a lot of uncertainties. But the [climate] models are getting a lot stronger," said Jay Gulledge, a senior research at the Pew Center on Global Climate Change in Arlington, Virginia.
Gulledge says some current projections point to a rise in average global temperature of 0.5°C (slightly less than 1°F) by the year 2030.
The estimates are based on greenhouse gasses already in the atmosphere. While the temperature increase is small, it would be significant. Over the past century Earth has warmed about 1°F (0.6°C). (See our fast facts on global warming.)
Gulledge cautions, however, that warming rates depend on many factors, some of which have yet to be discovered.
"One of the big unknowns is how society will react," said Antonio Busalacchi, a University of Maryland meteorologist who chairs the climate research committee for the National Academy of Sciences. "Are we going to change?
Meadow Offers Glimpse of Warmer Future
John Harte, an ecosystem sciences professor at the University of California, Berkeley, is already seeing possible future outcomes of global warming.
For 15 years, he has artificially heated sections of a Rocky Mountain meadow by about 3.6°F (2°C) to study the projected effects of global warming.
Harte has documented dramatic changes in the meadow's plant community. Sagebrush, though at the local altitude limit of its natural range, is replacing alpine flowers.
More tellingly, soils in test plots have lost about 20 percent of their natural carbon. This effect, if widespread, could dramatically increase Earth's atmospheric CO2 levels far above even conventional worst-case models.
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