Detecting the CO2 Fertilisation Effect from Space

Thursday, 18 December 2014
Tim McVicar, CSIRO Land and Water Canberra, Canberra, ACT, Australia, Randall J Donohue, CSIRO Land and Water Canberra, Canberra, Australia, Michael L Roderick, Australian National University, Canberra, Australia and Graham D Farquhar, Australian National University, Canberra, ACT, Australia
The global rise in atmospheric CO2 concentration enhances the rate at which vegetation can capture carbon through photosynthesis relative to the rate of water lost through transpiration. For arid environments, where the main limit to growth is the supply of water, this ‘fertilisation’ effect is expected to enhance overall vegetation cover and carbon capture, but there is no clear consensus on how the water cycle will be affected. Here, we present a simple model of how vegetation cover and carbon and water fluxes change with CO2 concentration, and we predict the historical (1982-2010) changes in these across the globe’s warm, dry environments. We test this model using concurrent satellite-derived vegetation cover data, processed to separate the CO2-driven changes in cover from changes associated with other dominant drivers (namely, precipitation and disturbances). For the 14% rise in CO2 concentration over the study period, our model predicted a 5-10% rise in vegetation cover which was confirmed by satellite observations that showed an 11% rise in cover. We discuss the implications of this work on catchment vegetation structure and carbon and water fluxes.