Question

The percentage of carbon dioxide in the atmosphere at present is the highest that it has been in the past 400,000 years

Answer 1

Scientists express them as parts per million, or ppm. In March 2011, carbon dioxide levels were at 391 ppm, which is 0.0391 percent of the atmosphere. This roughly corresponds to a mass of 3 trillion tons. After nitrogen, oxygen, water vapor and argon, carbon dioxide is the fifth most abundant gas in the atmosphere.

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