Q. Does the amount of carbon dioxide in the air go up during the winter because trees lose their leaves and grass is covered by snow?A. Seasonal changes in atmospheric carbon dioxide are well documented, says UW-Madison geography professor Jack Williams, with long-term records showing peaks every winter and troughs every summer.
The seasonal fluctuations are relatively small — roughly 2 percent of the total amount of carbon dioxide in the air — but are distinct even as overall carbon dioxide levels have been increasing.
These cyclic changes have been attributed to plants, which Williams says are sometimes called the "lungs" of the planet, "breathing in CO2 during the spring and summer when plants are growing … and breathing out CO2 in the fall and winter when leaves are coming off the trees."
Since the timing of the seasons is opposite in the Southern Hemisphere, he says, "Their ecosystems are breathing in CO2 when ours are exhaling it, and vice versa." However, the vast majority of land plants are found in the Northern Hemisphere, so northern seasons drive the overall pattern of atmospheric carbon dioxide.
— Produced in cooperation with University Communications
Curious? Look for Curiosities on Thursdays in the Local section. Send questions to: bwilliams@madison.com; 608-252-6130; Curiosities, P.O. Box 8058, Madison, WI 53708."
