WASHINGTON -- Heat-trapping greenhouse gases in the atmosphere are building up so high, so fast, that some scientists now think the world can no longer limit global warming to the level world leaders have agreed upon as safe.
New figures from the U.N. weather agency Monday showed that the three biggest greenhouse gases not only reached record levels last year but also were increasing at an ever-faster rate, despite efforts by many countries to reduce emissions.
As world leaders meet next week in South Africa to tackle the issue of climate change, several scientists said their projections show it is unlikely the world can hold warming to the target set by leaders just two years ago in Copenhagen.
"The growth rate is increasing every decade," said Jim Butler, director of the U.S. National Oceanic and Atmospheric Administration's Global Monitoring Division. "That's kind of scary."
Scientists can't say exactly what levels of greenhouse gases are safe, but some fear a continued rise in global temperatures will lead to irreversible melting of some of the world's ice sheets and a several-foot rise in sea levels over the centuries.
The findings from the U.N. World Meteorological Organization are consistent with other grim reports issued recently. Earlier this month, figures from the U.S. Department of Energy showed that global carbon dioxide emissions in 2010 jumped by the highest one-year amount ever.
The WMO found that total carbon dioxide levels in 2010 hit 389 parts per million, up from 280 parts per million in 1750, before the start of the Industrial Revolution. Levels increased 1.5 ppm per year in the 1990s and 2.0 per year in the first decade of this century, and are now rising at a rate of 2.3 per year. The top two other greenhouse gases -- methane and nitrous oxide -- are also soaring.
The U.N. agency cited fossil fuel burning, loss of forests that absorb CO2 and use of fertilizer as the main culprits.
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