Greater ecosystem carbon in the Mojave Desert after ten years exposure to elevated CO2

Carbon dioxide is the main greenhouse gas inducing climate change. Increased global CO₂ emissions, estimated at 8.4 Pg C yr⁻¹ at present, have accelerated from 1% yr⁻¹during 1990–1999 to 2.5% yr⁻¹ during 2000–2009 (ref. 1). 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 uncertain²; 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 CO₂ (ref. 3). Here we report significant terrestrial C accumulation caused by CO₂ enhancement to net ecosystem productivity in an intact, undisturbed arid ecosystem^{4, 5, 6, 7, 8} following ten years of exposure to elevated atmospheric CO₂. Results provide direct evidence that CO₂fertilization substantially increases ecosystem C storage and that arid ecosystems are significant, previously unrecognized, sinks for atmospheric CO₂ that must be accounted for in efforts to constrain terrestrial and global C cycles.