Global covariation of carbon turnover times with climate in terrestrial ecosystems

The response of the terrestrial carbon cycle to climatic change is among the largest uncertainties affecting future climate change projections1,2. The feedback between the terrestrial carbon cycle and climate is partly determined by changes in the residence time of carbon in land ecosystems, which in turn is an ecosystem property that emerges from the interplay between climate, soil, and vegetation type3,4,5,6. Here, we present a global, spatially explicit and observation-based assessment of whole-ecosystem carbon turnover times (τ) that combines new estimates of vegetation and soil organic carbon stocks and fluxes. We find that the overall mean global carbon turnover time is years (95% CI). On average, carbon resides in the vegetation and soil near the equator for a shorter time period than at latitudes north of 75ºN (mean τ of 15 and 255 years, respectively). We identify clear dependencies of τ on temperature, as expected based on our current understanding of temperature controls on ecosystem dynamics. Surprisingly, our analysis also reveals similarly strong associations of τ with precipitation. Moreover, we find that the ecosystem carbon turnover times simulated by state-of-the-art coupled climate carbon-cycle models vary widely and that numerical simulations, on average, tend to underestimate the global carbon turnover time by 36 per cent. The models show stronger spatial relationships with temperature than observation-based estimates, but generally do not reproduce the strong relationships with precipitation and predict faster carbon turnover in many semi-arid regions. Our findings suggest that future carbon cycle-climate feedbacks may depend more strongly on changes in the hydrological cycle than currently expected and considered in Earth system models.

CARVALHAIS Nuno;  FORKEL Matthias;  KHOMIK Myroslava;  BELLARBY Jessica;  JUNG Martin;  MIGLIAVACCA Mirco;  MU Mingquan;  SAATCHI Sassan;  SANTORO Maurizio;  THURNER Martin;  WEBER Ulrich;  AHRENS Bernhard;  BEER C.;  CESCATTI Alessandro;  RANDERSON James T.;  REICHSTEIN Markus; 

2015-01-26

NATURE PUBLISHING GROUP

JRC91107

0028-0836,   

http://www.nature.com/nature/journal/v514/n7521/full/nature13731.html,    https://publications.jrc.ec.europa.eu/repository/handle/JRC91107,   

10.1038/nature13731,