Enhanced Seasonal Exchange of CO2 by Northern Ecosystems - Observations and Models

Long-term measurements of atmospheric CO2 have revealed increasing amplitude in seasonal variations at Northern Hemisphere sites. In a recent paper1, we extended the analysis of seasonal CO2 amplitude using aircraft data from 1958-61 and 2009-11 and found large increases of 50% in the mid-troposphere north of 45 N. Changes in amplitude south of 45 N were less than 25%. The observations indicate that seasonal CO2 exchanges with northern terrestrial ecosystems must have increased by 30-60% over the past 50 years. The increased exchange is likely widespread over northern ecosystems but it must be focused in boreal forests to match the observed spatial pattern in the aircraft data. Small decreases in seasonal CO2 exchange of subtropical and tropical regions may also contribute to CO2 amplitude changes. The required increases in seasonal CO2 exchange in northern ecosystems are larger than …