Climate Number: 123 Petagrams of Carbon
Plants use the sun’s energy to turn carbon dioxide (CO2) in the air into the organic matter, or carbohydrates, that make up their bodies. This process, known as photosynthesis, ultimately feeds the rest of the food chain, with grazers eating the plants and carnivores and omnivores eating the grazers. How much carbon land plants take up each year, as well a how much carbon animals and fungi respirate back into the atmosphere, is important for understanding how much food, fiber and wood can be produced on a global scale. It is also important for predicting the future make-up of the atmosphere and climatic conditions. Estimates show that each year across Earth’s land surfaces, a total of around 123 petagrams (123,000,000,000,000,000 grams) of carbon are taken up by plants. Yet, about the same amount of carbon is respirated back into the air, in addition to the amount of fossilized carbon that goes into the atmosphere after being burnt in cars and power plants. The amount of carbon taken out of the atmosphere varies across the globe, with the Sahara Desert absorbing almost no carbon, while each square meter of the Amazon Rainforest absorbs an average of three kilograms (6.6 pounds) each year.
For comparison: U.S. wheat production is about 2.16 billion bushels per year, for a total weight (assuming 13 percent moisture content) of 58,800,000,000,000 grams (130 billion pounds). This is about 1/2092nd of the total amount of carbon that is taken up by land plants each year. For further comparison, 123 petagrams is about the same weight as a 1.3 million Nimitz Class aircraft carriers.
Seasons: Winter, Spring, Summer, Fall
Sources: Beer, C et al. “Terrestrial Gross Carbon Dioxide Uptake: Global Distribution and Covariation with Climate.” Science 329 (2010): 834-838 and Reich, PB. “The Carbon Dioxide Exchange.” Science 329 (2010): 774-775.
