CO2
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Hi, I'm Dave Thurlow for the Weather Notebook. Today we have a question from 10-year-old listener Sheeven Bhatt in Michigan. He writes: "I know that plants take in carbon dioxide to breathe. What happens in fall and winter when all the leaves are gone and most plants are sleeping? Does the amount of carbon dioxide increase in the air we breathe? Is our air dirtier in the winter than in spring? Please explain."

Does the amount of carbon dioxide, or CO2, in the air, increase in the winter when trees and plants lose their leaves? Yes, it does. The carbon dioxide absorbed by plants in the summer is released in the winter when photosynthesis either slows down, or stops. CO2 goes up in the winter and down in the summer.

Scientist Charles Keeling demonstrated this phenomenon in the 1950s. He sampled the air every day for years from a mountaintop in Hawaii, where the air very clean. He discovered that the amount of CO2 went up and down by a percent or two every year in a perfect cycle. He also noticed that the total amount of CO2 in the atmosphere increases every year because of carbon emissions or pollution.

Is air is dirtier in the winter than in the summer. That depends on where you are. On the average, all around the world, there is more CO2 in the air in the winter than there is in the summer. Thanks for the great question Sheeven.

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