Isn’t carbon dioxide a natural part of the atmosphere? If CO2 takes up such a small percentage of the atmosphere, why does it have such a big effect?
Return to Climate Question & Answers
Through most of human history, carbon dioxide made up about 280 out of every million molecules (parts per million) in a given volume of air in Earth’s troposphere. This concentration remained quite steady for thousands of years, with some CO2 being added by volcanic processes (plus a relatively small amount breathed out by animals) and some CO2 being absorbed by oceans, plants, and soil. This natural balance was thrown out of sync by the Industrial Revolution. Even though Earth is now absorbing almost half of the CO2 we emit through fossil fuels, the atmospheric concentration continues to rise year after year. It’s now close to 390 parts per million and still climbing by around 1.5 to 2.5 ppm per year. Even if we stopped burning all fossil fuels tomorrow, it would take more than 100 years for the CO2 we’ve already added to the atmosphere to be drawn back out of it by the oceans, vegetation, and soil.
Just as a tiny amount of hot pepper can transform a recipe, a little extra CO2 has a huge effect on our atmosphere. Ninety-nine (99) percent of the atmosphere, including nitrogen and oxygen, doesn’t interfere with radiation reflected from Earth back out to space. But greenhouse gases – all of which have three or more atoms – are able to intercept large amounts of that outgoing radiation. As noted in question 2, without CO2, Earth’s average temperature would be close to zero Fahrenheit. If we had several times our current concentration of CO2, then temperatures would skyrocket, as they did more than once during prehistoric periods.
More information: “The Carbon Dioxide Greenhouse Effect.” From: The Discovery of Global Warming, by Spencer Weart. American Institute of Physics