Unplanned geoengineering. Subject: Fwd: Boosts in productivity of corn and other crops modify Northern Hemisphere carbon dioxide cycle -- ScienceDaily.
*Boosts in productivity of corn and other crops modify Northern Hemisphere carbon dioxide cycle* http://www.sciencedaily.com/releases/2014/11/141119142211.htm In the Northern Hemisphere, there's a strong seasonal cycle of vegetation. Each year in the Northern Hemisphere, levels of atmospheric carbon dioxide drop in the summer as plants "inhale," then climb again as they exhale after the growing season. During the last 50 years, the size of this seasonal swing has increased by as much as half, for reasons that aren't fully understood. Now a team of researchers has shown that agricultural production may generate up to a quarter of the increase in this seasonal carbon cycle, with corn playing a leading role. *Agricultural Green Revolution as a driver of increasing atmospheric CO2 seasonal amplitude* http://www.nature.com/nature/journal/v515/n7527/full/nature13893.html?WT.ec_id=NATURE-20141120 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 and CO2 release during the autumn and winter seasons1, 2, 3,4. The CO2 seasonal amplitude has increased over the past five decades, suggesting an increase in Northern Hemisphere biospheric activity2, 5, 6. 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 amplitude2, 6, 7, 8, 9, 10, 11, 12, 13. 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 mid-latitude cropland between 25° N and 60° N and the high-latitude natural vegetation between 50° N and 70° N. The long-term trend of seasonal amplitude increase is 0.311 ± 0.027 per cent 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. *Direct human influence on atmospheric CO2 seasonality from increased cropland productivity* http://www.nature.com/nature/journal/v515/n7527/full/nature13893.html?WT.ec_id=NATURE-20141120 Ground- and aircraft-based measurements show that the seasonal amplitude of Northern Hemisphere atmospheric carbon dioxide (CO2) concentrations has increased by as much as 50 per cent over the past 50 years1, 2, 3. This increase has been linked to changes in temperate, boreal and arctic ecosystem properties and processes such as enhanced photosynthesis, increased heterotrophic respiration, and expansion of woody vegetation4, 5, 6. However, the precise causal mechanisms behind the observed changes in atmospheric CO2 seasonality remain unclear2, 3, 4. Here we use production statistics and a carbon accounting model to show that increases in agricultural productivity, which have been largely overlooked in previous investigations, explain as much as a quarter of the observed changes in atmospheric CO2 seasonality. Specifically, Northern Hemisphere extratropical maize, wheat, rice, and soybean production grew by 240 per cent between 1961 and 2008, thereby increasing the amount of net carbon uptake by croplands during the Northern Hemisphere growing season by 0.33 petagrams. Maize alone accounts for two-thirds of this change, owing mostly to agricultural intensification within concentrated production zones in the midwestern United States and northern China. Maize, wheat, rice, and soybeans account for about 68 per cent of extratropical dry biomass production, so it is likely that the total impact of increased agricultural production exceeds the amount quantified here. ᐧ -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
