Greater ecosystem carbon in the Mojave Desert after ten years exposure to elevated CO 2

Carbon dioxide is the main greenhouse gas inducing climate change. Increased global CO 2 emissions, estimated at 8.4 Pg C yr a ̂'1 at present, have accelerated from 1% yr a ̂'1 during 1990-1999 to 2.5% yr a ̂'1 during 2000-2009 (ref.). The carbon balance of terrestrial ecosystems is the greatest unknown in the global C budget because the actual magnitude, location and causes of terrestrial sinks are uncertain; estimates of terrestrial C uptake, therefore, are often based on the residuals between direct measurements of the atmospheric sink and well-constrained models of ocean uptake of CO 2 (ref.). Here we report significant terrestrial C accumulation caused by CO 2 enhancement to net ecosystem productivity in an intact, undisturbed arid ecosystem following ten years of exposure to elevated atmospheric CO 2. Results provide direct evidence that CO 2 fertilization substantially increases ecosystem C storage and that arid ecosystems are significant, previously unrecognized, sinks for atmospheric CO 2 that must be accounted for in efforts to constrain terrestrial and global C cycles.