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We are currently at 390 part per million of carbon dioxide in the atmosphere. 350.org's Bill McKibben (who was on Colbert last night!), NASA's James Hansen, and countless other scientists say that 350 ppm is the upper most safe limit of CO2 in the sky. At the international climate negotiations in Bonn last week, the Least Developed Countries have joined up with the Alliance of Small Island States to say that 350 represents the bottom of what's acceptable in any climate agreement that comes out of Copenhagen in December.According to a letter that the LDCs and ASIS released on Friday, reducing emissions to a safe level means to "return atmospheric greenhouse gas concentrations to 350." The LDC group along with ASIS represents 80 countries.
What Would It Take to Get Us Back to 350?
Before the industrial revolution, the atmosphere contained 275ppm of carbon dioxide. But after 200 years of burning coal and burning oil, the atmosphere is now about 390ppm. To get it back down to 350, we need to dramatically cut our emissions.
In a scientific paper titled "Target atmospheric CO2: Where should humanity aim?", Dr. James Hansen argued that we need to get back to 350 as soon as possible. To do it, we need to stop building coal plants today and quickly phase out their use. By 2050, we need to be as close to zero emissions as possible.
The world's biggest emitters have not adopted the 350ppm goal. To do so would go much farther than they appear willing to go. The G8, which includes the US, did however recently agree to set a target of keeping temperature as far below a 2 degrees Celsius rise as possible.