CMIP5 Earth System Models

Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Abstract Superimposed on the continued increase in the atmospheric CO 2 concentration is a prominent seasonal cycle. Ground-based and aircraft-based observation records show that the amplitude of this seasonal cycle has increased. Will this trend continue into future? In this paper, we analyzed simulations for historical (1850–2005) and future 5 (RCP8.5, 2006–2100) periods produced by 10 Earth System Models participating the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5). Our results show a model consensus that the increase of CO 2 seasonal amplitude continues throughout the 21st century. The seasonal amplitude of the multi-model global mean detrended CO 2 increases from 1.6 ppm during 1961–1970 to 2.7 ppm during 2081–2090, and 10 the mean relative amplitude increases by 62 ± 19 %. This increase is dominated by a 68 ± 25 % increase from Net Biosphere Production (NBP). We then show the increase of NBP amplitude mainly comes from enhanced ecosystem uptake during Northern Hemisphere growing season under future CO 2 and temperature conditions. Separate analyses on net primary production and respiration reveal that enhanced ecosystem 15 carbon uptake contributes to about 75 % of the amplitude increase. Stimulated by higher CO 2 concentration and high-latitude warming, enhanced net primary production likely outcompetes increased respiration at higher temperature. Zonal distribution and the spatial pattern of NBP change suggest that regions north of 45 • N dominate the amplitude increase. We also found that changes of NBP and its seasonal ampli-20 tude are significantly (R = 0.73, p < 0.05) correlated – models that simulate a stronger carbon uptake tend to show a larger change of NBP seasonal amplitude.