Detection of a direct carbon dioxide effect in continental river runoff records.
Continental runoff has increased through the twentieth century despite more intensive human water consumption. Possible reasons for the increase include: climate change and variability, deforestation, solar dimming, and direct atmospheric carbon dioxide (CO2) effects on plant transpiration. All of these mechanisms have the potential to affect precipitation and/or evaporation and thereby modify runoff. Here we use a mechanistic land-surface model and optimal fingerprinting statistical techniques to attribute observational runoff changes into contributions due to these factors. The model successfully captures the climate-driven inter-annual runoff variability, but twentieth-century climate alone is insufficient to explain the runoff trends. Instead we find that the trends are consistent with a suppression of plant transpiration due to CO2-induced stomatal closure. This result will affect projections of freshwater availability, and also represents the detection of a direct CO2 effect on the functioning of the terrestrial biosphere.
Met Office, Hadley Centre for Climate Prediction and Research (JCHMR), Maclean Building, Wallingford OX10 8BB, UK. nicola.gedney@metoffice.gov.uk
N
N
Gedney
P M
PM
Cox
R A
RA
Betts
O
O
Boucher
C
C
Huntingford
P A
PA
Stott
D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D017753:Ecosystem; D005843:Geography; D017752:Greenhouse Effect; D018526:Plant Transpiration; D010944:Plants / Q000378:metabolism; D011891:Rain; D045483:Rivers; D012623:Seawater / Q000737:chemistry*; D013997:Time Factors; D014881:Water Supply
D002245:Carbon Dioxide; D002244:Carbon