Journal Article

An estimate of equilibrium sensitivity of global terrestrial carbon cycle using NCAR CCSM4

Nemani, Ramakrishna, Cao, Long, Narayanappa, Devaraju, Caldeira, Ken, Bala, G., Krishna, Sujith

2013

Overview

Increasing concentrations of atmospheric CO 2 influence climate, terrestrial biosphere productivity and ecosystem carbon storage through its radiative, physiological and fertilization effects. In this paper, we quantify these effects for a doubling of CO 2 using a low resolution configuration of the coupled model NCAR CCSM4. In contrast to previous coupled climate-carbon modeling studies, we focus on the near-equilibrium response of the terrestrial carbon cycle. For a doubling of CO 2 , the radiative effect on the physical climate system causes global mean surface air temperature to increase by 2.14 K, whereas the physiological and fertilization on the land biosphere effects cause a warming of 0.22 K, suggesting that these later effects increase global warming by about 10 % as found in many recent studies. The CO 2 -fertilization leads to total ecosystem carbon gain of 371 Gt-C (28 %) while the radiative effect causes a loss of 131 Gt-C (~10 %) indicating that climate warming damps the fertilization-induced carbon uptake over land. Our model-based estimate for the maximum potential terrestrial carbon uptake resulting from a doubling of atmospheric CO 2 concentration (285–570 ppm) is only 242 Gt-C. This highlights the limited storage capacity of the terrestrial carbon reservoir. We also find that the terrestrial carbon storage sensitivity to changes in CO 2 and temperature have been estimated to be lower in previous transient simulations because of lags in the climate-carbon system. Our model simulations indicate that the time scale of terrestrial carbon cycle response is greater than 500 years for CO 2 -fertilization and about 200 years for temperature perturbations. We also find that dynamic changes in vegetation amplify the terrestrial carbon storage sensitivity relative to a static vegetation case: because of changes in tree cover, changes in total ecosystem carbon for CO 2 -direct and climate effects are amplified by 88 and 72 %, respectively, in simulations with dynamic vegetation when compared to static vegetation simulations.

• Publisher: Springer-Verlag,Springer,Springer Nature B.V
• Subject: Air temperature / Animal and plant ecology / Animal, plant and microbial ecology / Atmospheric carbon dioxide / Biological and medical sciences / Biosphere / Carbon cycle / Carbon cycle (Biogeochemistry) / Carbon dioxide / Carbon sequestration / Climate change / Climate effects / Climate models / Climate system / Climatology / Climatology. Bioclimatology. Climate change / Earth and Environmental Science / Earth Sciences / Earth, ocean, space / Ecosystems / Environmental aspects / Equilibrium / Estimating techniques / Exact sciences and technology / External geophysics / Fundamental and applied biological sciences. Psychology / Geophysics/Geodesy / Global warming / Meteorology / Oceanography / Physiological aspects / Physiology / Sensitivity analysis / Storage capacity / Surface temperature / Synecology / Terrestrial ecosystems / Terrestrial environments / Vegetation / Water storage