Carbon dioxide already in danger zone, w...(reds of years. The scientists from the ...)

The scientists, from the United States, United Kingdom and France, are optimistic that current atmospheric CO2 could be reduced if emissions from coal, the largest contributor, are largely phased out by 2030. Use of unconventional fossil-fuel sources such as tar sands also would have to be minimized, they say. They predict that oil use will probably decline anyway as reserves shrink. So-called "geoengineering" solutions that would remove CO2 from the air have been proposed by others, but the group is skeptical; they estimate that artificially removing 50ppm of CO2 from the atmosphere would cost at least $20 trillion, or twice the current U.S. national debt. They suggest that reforestation of degraded land and use of more natural fertilizers could draw down CO2 by a similar amount.

"Humanity today, collectively, must face the uncomfortable fact that industrial civilization itself has become the principal driver of global climate," says the paper. "The greatest danger is continued ignorance and denial, which would make tragic consequences unavoidable."

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