‘A clear signal of widespread changes in northern ecosystems’
By Summit Voice
FRISCO — The Earth breathes in seasonal cycles, exhaling and inhaling great gulps of carbon dioxide as plant life goes through its annual cycle of growth.
And lately, those breaths have become up to 50 percent deeper, as more carbon dioxide is emitted from burning fossil fuels and other human activities, according to a study led by scientists at the Scripps Institution of Oceanography.
Levels of carbon dioxide in the atmosphere rise and fall each year as plants, through photosynthesis and respiration, take up the gas in spring and summer, and release it in fall and winter. But the amplitude of that cycle is intensifying, scientists say after studying data from several year’s worth of airborne chemistry sampling done in a series of pole to pole sampling flights.
In the study, the scientists compared the recent aircraft data with aircraft data gathered from 1958 to 1961 using U.S. Air Force weather reconnaissance flights.
“This research provides dramatic evidence of the significant influence the land-based biosphere can have on the amplitude [amount of change] in seasonal trends of carbon dioxide exchange,” said Sylvia Edgerton, program director in NSF’s Division of Atmospheric and Geospace Sciences, which funded the research.
Observations of atmospheric carbon dioxide made by aircraft at altitudes between 3 and 6 kilometers (10,000-20,000 feet) show that seasonal carbon dioxide variations have substantially changed during the last 50 years.
The amplitude increased by roughly 50 percent across high latitude regions north of 45 degrees North, compared with 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, said study lead scientist Heather Graven of SIO.
It’s not yet understood why the increase in seasonal amplitude of carbon dioxide concentration is so large, but it’s a clear signal of widespread changes in northern ecosystems, Graven said.
“The atmospheric carbon dioxide observations are important because they show the combined effect of ecological changes over large regions,” said Graven.”This reinforces ground-based studies that show that substantial changes are occurring as a result of rising carbon dioxide concentrations, warming temperatures and changing land management, including the expansion of forests in some regions and the poleward migration of ecosystems.”
The older data were analyzed by SIO geochemist Charles David Keeling, the father of Ralph Keeling, also an SIO scientist and a member of the research team. These aircraft measurements were done at the time Charles Keeling was beginning continuous carbon dioxide measurements at Mauna Loa, Hawaii. While the Mauna Loa measurements are now widely recognized as the “Keeling Curve,” the early aircraft data were all-but-forgotten.
The study confirmed similar findings from two ground-based stations, at Mauna Loa and Barrow, Alaska and show show the large area in northern high latitudes where carbon dioxide amplitude increased strongly since 1960.
Results of the study are reported in a paper published online this week by the journal Science. The National Science Foundation (NSF), along with the U.S. Department of Energy, the National Center for Atmospheric Research (NCAR), the National Oceanic and Atmospheric Administration (NOAA) and the Office of Naval Research funded the research.