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The Boston Globe

Science

Carbon levels accelerate, UN says

GENEVA — World carbon dioxide pollution levels in the atmosphere are accelerating and reached a record high in 2012, the UN weather agency said Wednesday.

The heat-trapping gas, pumped into the air by cars and smokestacks, was measured at 393.1 parts per million last year, up 2.2 ppm from the previous year, said the Geneva-based World Meteorological Organization in its annual greenhouse gas inventory.

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That is far beyond the 350 ppm that some scientists and environmental groups promote as the upper limit for a safe level.

The increase of carbon dioxide, the chief gas blamed for global warming, outpaced the past decade’s average annual increase of 2.02 ppm.

Based on that rate, the organization says, the world’s carbon dioxide pollution level is expected to cross the 400 ppm threshold by 2016. That level already was reached at some measurement stations in 2012 and 2013.

Scientists say the Earth probably last had this much carbon dioxide in the atmosphere a few million years ago, when sea levels were higher. Carbon dioxide levels were around 280 ppm before the Industrial Revolution.

Carbon dioxide accounts for three-quarters of the planet’s heat-trapping gases, which scientists say are causing sea levels to rise, glaciers to melt, and some weather patterns to change.

Methane, another destructive greenhouse gas, traps heat much more effectively but has a shorter life span.

Atmospheric methane also reached a new high of 1,819 parts per billion in 2012, which is 260 percent higher than the pre-industrial level. Methane comes from natural sources such as wetlands and termites and human activities such as cattle breeding.

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