B14D-01:
Intensification of Climate-Carbon Feedbacks after 2100 and Implications for Disturbance Regimes

Monday, 15 December 2014: 4:00 PM
James Tremper Randerson1, Keith T Lindsay2, Ernesto Munoz3, Weiwei Fu1, Forrest M Hoffman4, Jefferson Keith Moore1, Scott C Doney5, Natalie M Mahowald6 and Gordon B Bonan3, (1)University of California Irvine, Irvine, CA, United States, (2)National Center for Atmospheric Research, Climate & Global Dynamics Division, Boulder, CO, United States, (3)National Center for Atmospheric Research, Boulder, CO, United States, (4)University of California Irvine, Department of Earth System Science, Irvine, CA, United States, (5)Woods Hole Oceanographic Inst, Woods Hole, MA, United States, (6)Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, United States
Abstract:
Long-term ecosystem and carbon cycle responses to climate change are needed to inform mitigation policy, yet our understanding of how these responses may evolve after 2100 remains highly uncertain. Using the Community Earth System Model (version 1.0), we quantified climate-carbon feedbacks from 1850 to 2300 for the Representative Concentration Pathway 8.5 (and its extension). In three simulations, land and ocean biogeochemical models were exposed to the same trajectory of increasing atmospheric CO2. In one simulation, atmospheric CO2 and other forcing agents were radiatively active (fully coupled), modifying temperature and other aspects of climate. In another, CO2 was radiatively uncoupled, and in the third, both CO2 and other atmospheric forcing agents (including CH4, N2O, and aerosols) were radiatively uncoupled. In the fully coupled simulation, global mean air temperatures increased by 9.3°C from 1850 to 2300, with 4.4°C of this warming occurring after 2100. Without radiative forcing from CO2, cumulative warming was much lower at 2.4°C, but exceeding 2°C targets needed to avoid dangerous interference with the climate system. In response to climate change, ocean and land rates of carbon uptake were reduced, with the size of the impact increasing over time. In the oceans, reductions in cumulative carbon uptake from climate change increased from 3% during the 20th century to 40% during the 23rd century. By 2300, climate change had reduced cumulative ocean uptake by 330 Pg C, from 1410 Pg C to 1080 Pg C. Most of this reduction occurred after 2100 as a consequence of increases in surface stratification and decreases in Atlantic meridional overturning circulation. Land fluxes similarly diverged over time, with climate change inducing a cumulative loss of 230 Pg C by 2300. On land the intensification of the hydrological cycle globally increased terrestrial water storage, although asymmetric responses were observed across different continents in the tropics. Net loss of carbon from tropical forest ecosystems, in response to large temperature increases, were partly offset by increases in carbon uptake in temperate and high latitude ecosystems. We conclude by presenting an assessment of how climate variability over land and burned area change century by century.