CO2 emissions: the magic number
What is the current atmospheric concentration of carbon dioxide?
The Globalist in The Seattle Times,, January 26, 2009
Amid growing public awareness about the dangers of global warming, business and political leaders — as well as everyday citizens — are trying to find ways to reduce carbon-dioxide emissions. What is the current atmospheric concentration of carbon dioxide?
A. 280 parts per million
B. 385 parts per million
C. 450 parts per million
D. 550 parts per million
What is the current atmospheric concentration of carbon dioxide?
A. 280 parts per million is not correct.
For a few millennia before 1800, the concentration of carbon dioxide in the atmosphere was about 280 parts per million. About 200 years ago, the world released about 10 million tons of carbon dioxide per year through burning fossil fuels. By 1950, annual carbon emissions stood at 1.6 billion tons and the atmospheric concentration of carbon dioxide reached 311 parts per million.
B. 385 parts per million is correct.
The current atmospheric concentration of carbon dioxide is about 385 parts per million, according to the Earth Policy Institute. Almost all of this 38 percent increase since the preindustrial era is due to human activity, with humans having released nearly 8.4 billion tons into the atmosphere through the burning of fossil fuels in 2006 alone. Global carbon-dioxide concentration is increasing by about two parts per million per year. Assuming that current trends continue, the atmospheric concentration of greenhouse gases would reach 1,000 parts per million by 2100. This would result in a global temperature increase of up to 11 degrees.
C. 450 parts per million is not correct.
A generally accepted goal of a relatively "safe" level of carbon-dioxide concentration (in terms of its likely climate-change consequences) is about 440 parts per million. A greenhouse-gas concentration of 450 would increase global temperatures by about 3.5 degrees. To achieve this level by 2030, emissions in OECD countries would need to be reduced by almost 40 percent compared with 2006 levels. Other major economies would need to limit emissions growth to 20 percent.
D. 550 parts per million is not correct.
In the long term, atmospheric carbon-dioxide concentration is on a path to easily exceed 550 parts per million. However, limiting carbon dioxide to this level would result in a global temperature increase of 5.5 degrees — reducing the probability of dangerous climate change.
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