Levels of carbon dioxide in the atmosphere rise and fall annually as plants take up the gas in spring and summer and release it in fall and winter through photosynthesis and respiration. Now the range of that cycle is growing as more CO2 is emitted from the burning of fossil fuels and other human activities, according to a study led by Scripps Institution of Oceanography at the University of California, San Diego.

The findings are the result of a multiyear airborne survey of atmospheric chemistry called HIAPER Pole-to-Pole Observations (HIPPO). Steven C. Wofsy, Abbott Lawrence Rotch Professor of Atmospheric and Environmental Science at the Harvard School of Engineering and Applied Sciences (SEAS), is lead principal investigator of the HIPPO project. HIPPO research flights from the Arctic to the Antarctic produced an unprecedented portrait of greenhouse gases and particles in the atmosphere, the first detailed three-dimensional mapping of the global distribution of gases and particles that affect Earth’s climate.

Observations of atmospheric CO2 made at altitudes between 3 and 6 kilometers (10,000–20,000 feet) show that seasonal CO2 variations have substantially increased in amplitude over the past 50 years. The amplitude increased by roughly 50 percent across high latitude regions north of 45°N, in comparison to previous aircraft observations from the late 1950s and early 1960s.

This means that more carbon is accumulating in forests and other vegetation and soils in the Northern Hemisphere during the summer, and more carbon is being released in the fall and winter.

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