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Title: Reduction in carbon uptake during turn of the century drought in western North America

item SCHWALM, C.R. - Clark University
item WILLIAMS, C.A. - Clark University
item SCHAEFER, K. - University Of Colorado
item BALDOCCHI, D. - University Of California
item BLACK, T.A. - University Of British Columbia
item GOLDSTEIN, A.H. - University Of California
item LAW, B.E. - Oregon State University
item OECHEL, W.C. - San Diego State University
item PAW U., K.T. - University Of California
item Scott, Russell - Russ

Submitted to: Nature Geoscience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2012
Publication Date: 7/29/2012
Citation: Schwalm, C., Williams, C., Schaefer, K., Baldocchi, D., Black, T., Goldstein, A., Law, B., Oechel, W., Paw U., K., Scott, R.L. 2012. Reduction in carbon uptake during turn of the century drought in western North America. Nature Geoscience. 5: 551-556.

Interpretive Summary: Land-based ecosystems sequester much of the carbon dioxide that is released from burning fossil fuels. Here we show that the 2000 to 2004 turn of the century drought in western North America resulted in a loss of ecosystem productivity and a reversal of normal land sequestration of carbon dioxide. We document a pronounced drying of the terrestrial biosphere, severely decreased river discharge, and a loss in cropland productivity during this drought. Further analysis shows that the drought extent, duration, and severity of the turn of the century drought was unprecedented over the last 800 years. Our results also indicate that forecasted changes in precipitation and drought severity could permanently disable the net carbon sequestration in western North America by around 2050. Furthermore the dry conditions in 2000 to 2004 are expected to become the wet end of a new climatology consistent with the beginning of a modern megadrought.

Technical Abstract: Fossil fuel emissions aside, temperate North America is a net sink of carbon dioxide at present1–3. Year-to-year variations in this carbon sink are linked to variations in hydroclimate that affect net ecosystem productivity3,4. The severity and incidence of climatic extremes, including drought, have increased as a result of climate warming5–8. Here, we examine the effect of the turn of the century drought in western North America on carbon uptake in the region, using reanalysis data, remote sensing observations and data from global monitoring networks.We show that the area-integrated strength of the western North American carbon sink declined by 30–298 Tg C yr''1 during the 2000–2004 drought. We further document a pronounced drying of the terrestrial biosphere during this period, together with a reduction in river discharge and a loss of cropland productivity. We compare our findings with previous palaeoclimate reconstructions7 and show that the last drought of this magnitude occurred more than 800 years ago. Based on projected changes in precipitation and drought severity, we estimate that the present mid-latitude carbon sink of 177–623 Tg C yr''1 in western North America could disappear by the end of the century.