Agricultural Green Revolution as a driver of increasing atmospheric CO2 seasonal amplitude

Ning Zeng, University of Maryland, zeng@atmos.umd.edu
Fang Zhao, University of Maryland, fzhao@atmos.umd.edu (Presenter)
George James Collatz, NASA GSFC, jim.collatz@nasa.gov
Eugenia Kalnay, University of Maryland, ekalnay@atmos.umd.edu
Ross Salawitch, University of Maryland, rjs@atmos.umd.edu
Tristram O. West, White House Council on Environmental Quality, tristram_o_west@ceq.eop.gov
Guanter Luiz, luis.guanter@wew.fu-berlin.de, freie universität berlin
Ghassem Asrar, PNNL, ghassem.asrar@pnnl.gov

The atmospheric carbon dioxide (CO2) record displays a prominent seasonal cycle that arises mainly from changes in vegetation growth and the corresponding CO2 uptake during the boreal spring and summer growing seasons andCO2 release during the autumn and winter seasons. The CO2 seasonal amplitude has increased over the past five decades, suggesting an increase in Northern Hemisphere biospheric activity. It has been proposed that vegetation growth may have been stimulated by higher concentrations of CO2 as well as by warming in recent decades, but such mechanisms have been unable to explain the full range and magnitude of the observed increase in CO2 seasonal amplitude. Here we suggest that the intensification of agriculture (the Green Revolution, in which much greater crop yield per unit area was achieved by hybridization, irrigation and fertilization) during the past five decades is a driver of changes in the seasonal characteristics of the global carbon cycle. Our analysis of CO2 data and atmospheric inversions shows a robust 15 per cent long-term increase in CO2 seasonal amplitude from 1961 to 2010, punctuated by large decadal and interannual variations. Using a terrestrial carbon cycle model that takes into account high-yield cultivars, fertilizer use and irrigation, we find that the long-term increase in CO2 seasonal amplitude arises from two major regions: the midlatitude cropland between 256N and 606N and the high-latitude natural vegetation between 506Nand706 N. The long-term trend of seasonal amplitude increase is 0.31160.027 percent per year, of which sensitivity experiments attribute 45, 29 and 26 per cent to land-use change, climate variability and change, and increased productivity due to CO2 fertilization, respectively. Vegetation growth was earlier by one to two weeks, as measured by the mid-point of vegetation carbon uptake, and took up 0.5 petagrams more carbon in July, the height of the growing season, during 2001–2010 than in 1961–1970, suggesting that human land use and management contribute to seasonal changes in the CO2 exchange between the biosphere and the atmosphere.

Presentation Type:  Poster

Session:  Carbon Monitoring System (CMS) Posters   (Mon 1:30 PM)

Associated Project(s): 

• Asrar, Ghassem: Carbon Monitoring of Agricultural Lands: Developing a Globally Consistent Estimate of Carbon Stocks and Fluxes ...details
• Collatz, Jim: Improving and extending CMS land surface carbon flux products including estimates of uncertainties in fluxes and biomass ...details

Poster Location ID: 176