THEGREENGROK    Statistically Speaking

The Climate Clock

by Bill Chameides | September 17th, 2010
posted by Erica Rowell (Editor)

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The time for slowing greenhouse gas emissions is slipping away.

The United States along with some 110 other nations have committed to not allowing concentrations of carbon dioxide (CO2) to exceed 450 parts per million (ppm) so that global temperatures will not rise more than 3.5 degrees Fahrenheit (2 degrees Celsius) above pre-industrial levels. (Learn more about the Copenhagen Accord [pdf], in which some 76 countries [see here and here] have made voluntary pledges to reduce CO2.)

Since agreeing, however, there’s been a whole lot of dithering and very little action. Can we afford much more dithering? You be the judge.

Carbon Numbers of Note Billion tons
(Gigatons) of Carbon
Total amount of carbon in pre-industrial atmosphere1 560
Total amount of carbon in today’s atmosphere2 780
Total amount of carbon in atmosphere with 450 ppm CO2 900
Total CO2 emissions of carbon since industrial revolution3 500
Maximum total amount of carbon that can be emitted globally
by mid-century without exceeding 450 ppm CO2 concentration
U.S. allotment of the 250-gigaton emissions maximum4  50
Current amount of carbon emitted globally each year    8
Current amount of CO2 emitted by U.S. each year    2


The Ticking Climate Clock Years
Time left for international community to exceed
450 ppm at current emissions rate
Time left for U.S. to exceed its allotment at current emissions rate 25


And for Comparison … Years
The average lifespan of a coal-fired power plant 50–75

And one other nugget: Both U.S. [pdf] and global emissions are projected to increase in the coming decade.

Tick tock, tick tock.



One ppm of CO2 in the atmosphere is equivalent to two gigatons of carbon.

1Pre-industrial CO2 concentration was about 280 ppm.

2Current CO2 concentrations are approximately 389 ppm.

3Roughly 40-50 percent of CO2 emissions stay in the atmosphere.

4This U.S. allotment is derived from a model that allows the international community to meet the 250-billion-ton maximum at minimal cost.

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