Nonlinear Interactions between Climate and Atmospheric Carbon Dioxide Drivers of Terrestrial and Marine Carbon Cycle Changes from 1850 to 2300

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1 Nonlinear Interactions between Climate and Atmospheric Carbon Dioxide Drivers of Terrestrial and Marine Carbon Cycle Changes from 1850 to 2300 Forrest M. Hoffman 1,2, James T. Randerson 2, J. Keith Moore 2, Michael L. Goulden 2, Weiwei Fu 2, Charles D. Koven 3, Abigail L. S. Swann 4, Natalie M. Mahowald 5, Keith Lindsay 6, Ernesto Muñoz 6, and Gordon B. Bonan 6 1 Oak Ridge National Laboratory, 2 University of California Irvine, 3 Lawrence Berkeley National Laboratory, 4 University of Washington Seattle, 5 Cornell University, and 6 National Center for Atmospheric Research Japan Geoscience Union (JpGU) Meeting Makuhari Messe, Chiba, Japan May 22 26, 2016

2 Science Question To what degree do the effects of climate change due to warming and CO 2 fertilization in isolation combine linearly? Radiative Forcing for RCPs and ECPs RCP 8.5 Fossil CO 2 Emissions Fossil CO 2 Emissions (PgC y) Meinshausen et al. (2011) extended RCP forcings out to C O = β O CO 2 + γ O T C L = β L CO 2 + γ L T g = α (γ O + γ L ) (m + β O + β L ) From Friedlingstein et al. (2006). Radiative Coupling Biogeochemical Coupling Simulation Other GHG Nitrogen Land Experiment Identifier CO 2 & aerosols CO 2 deposition use Name bcrd bdrcs.pftcon bdrd.pftcon Transient anthropogenic forcing Constant pre-industrial (1850) forcing

3 T Climate Carbon Cycle Drivers ( ) net land uptake T 2m (K) (Pg C y 1 ) net ocean CO uptake 2 (ppm) (Pg C y 1 ) net ocean uptake (Pg C y 1 ) Climate Carbon Cycle Drivers and Uptake ( ) (a) (c) + 1 ( + ) = 0.43 (b) (d) 1 ( + ) = (c) (c) (a) Prescribed atmospheric CO 2 mole fraction was stabilized at 1962 ppm around (b) 2 m air temperature increased by 9.4 C in, 8.9 C in, and 1.0 C in simulations. (c) Mean air temperature over land increased by 11.6 C in the simulation and approached 25 C at high latitudes.

4 Net Ocean and Land Carbon Uptake ( ) net ocean carbon storage ( ) Cumulative FGCO2 (Pg C) ( + ) = Net ocean carbon storage has a nonlinear response that Schwinger et al. (2014) attributed to surface stratification under climate change that restricted C penetration into intermediate and deep waters. Cumulative NBP (Pg C) net land carbon storage ( ) + 1 ( + ) = Net land carbon storage also has a nonlinear response, of opposite sign, that has not been explored in ESMs, although Zickfeld et al. (2011) explored similar nonlinear responses in an EMIC. It is driven by larger than expected productivity increases due to positive hydrological and nitrogen mineralization feedbacks.

5 Ocean and Land Climate Carbon Sensitivities net ocean carbon storage climate sensitivity ( ) The difference between the net ocean carbon storage climate sensitivities, γo and γ O, was nearly 27 Pg C K 1 and continued to diverge at the end of the 23 rd century. γ O (Pg C K 1 ) ( ) net land carbon storage climate sensitivity ( ) The difference between the net land carbon storage climate sensitivities, γl and γ L, peaked at about 10 Pg C K 1 around 2175 and ended at about 4 Pg C K 1 at γ L (Pg C K 1 ) ( )

6 Climate Sensitivities and Climate Carbon Cycle Gains α (K ppm 1 ) g (unitless) Climate Sensitivities and Feedback Gains ( ) (a) (b) β, γ β, γ β, γ β, γ E C, E C The climate sensitivity, α, for the simulation was about K ppm 1 at the end of the 23 rd century. The climate carbon cycle gain* (g) clustered around two different values, depending on the method and experiments used to calculate it, and at 2300 was 42% higher when estimated from sensitivity parameters derived from ( ) than from. *This gain included effects of aerosols and other greenhouse gases.

7 Drivers of Nonlinear Terrestrial Uptake Responses 5 y mean gross primary production ( ) 5 y mean nitrogen mineralization ( ) GPP (Pg C/y) ( + ) = N mineral (Pg N/y) ( + ) = y mean total precipitation ( ) 5 y mean evapotranspiration ( ) Precip (mm/d) ( + ) = ET (mm/d) ( + ) = Enhanced gross primary production (GPP) and higher rates of N mineralization, driven by excess precipitation increases and reduced evapotranspiration, led to the nonlinear C uptake response on land under simultaneous climate change and elevated CO 2 levels.

8 Nonlinear GPP Responses Across Model Experiments = (f) (e) (d) (g) = (c) (b) (a) (h) = (i)

9 1.0 Drivers of Hydrological and Ecological Changes ( ) NL T at 2m SH LH N mineral Precip RH at 2m P ET ET Transp SMoist Runoff GPP NPP ER HR LAI Land C storage Ocean C storage Energy & N Water Carbon

10 Summary and Conclusions Science Question To what degree do the effects of climate change due to warming and CO 2 fertilization in isolation combine linearly? simulations yielded a net ocean carbon storage climate sensitivity (γ O ) that was weaker and a net land carbon storage sensitivity (γ L ) that was stronger than those diagnosed from and simulations. For the ocean, the nonlinearity was associated with warming-induced weakening of ocean circulation and mixing, which limited exchange of dissolved inorganic carbon between surface and deeper water masses. For the land, the nonlinearity was associated with strong gains in gross primary production in the simulation, driven by enhancements in the hydrological cycle and increased nutrient availability. The feedback gain (g) at 2300 was 42% higher when estimated from sensitivity parameters derived from ( ) than from. We recommend deriving γ O and γ L This gain included effects of aerosols and other greenhouse gases. in future studies.

11 Acknowledgments This research was supported by the Bigeochemistry Climate Feedbacks ( Feedbacks) Scientific Focus Area, which is sponsored by the Regional and Global Climate Modeling Program in the Climate and Environmental Sciences Division (CESD) of the Biological and Environmental Research (BER) Program in the U.S. Department of Energy Office of Science, and by the National Science Foundation (AGS ). This research used resources of the National Center for Computational Sciences (NCCS) at Oak Ridge National Laboratory (ORNL), which is managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.

12 References P. Friedlingstein, P. M. Cox, R. A. Betts, L. Bopp, W. von Bloh, V. Brovkin, S. C. Doney, M. Eby, I. Fung, B. Govindasamy, J. John, C. D. Jones, F. Joos, T. Kato, M. Kawamiya, W. Knorr, K. Lindsay, H. D. Matthews, T. Raddatz, P. Rayner, C. Reick, E. Roeckner, K.-G. Schnitzler, R. Schnur, K. Strassmann, S. Thompson, A. J. Weaver, C. Yoshikawa, and N. Zeng. Climate carbon cycle feedback analysis, results from the C 4 MIP model intercomparison. J. Clim., 19(14): , July doi: /jcli M. Meinshausen, S. Smith, K. Calvin, J. Daniel, M. Kainuma, J.-F. Lamarque, K. Matsumoto, S. Montzka, S. Raper, K. Riahi, A. Thomson, G. Velders, and D. P. van Vuuren. The RCP greenhouse gas concentrations and their extensions from 1765 to Clim. Change, 109(1): , Nov doi: /s z. J. Schwinger, J. F. Tjiputra, C. Heinze, L. Bopp, J. R. Christian, M. Gehlen, T. Ilyina, C. D. Jones, D. Salas-Mélia, J. Segschneider, R. Séférian, and I. Totterdell. Nonlinearity of ocean carbon cycle feedbacks in CMIP5 Earth system models. J. Clim., 27(11): , June doi: /jcli-d K. Zickfeld, M. Eby, H. D. Matthews, A. Schmittner, and A. J. Weaver. Nonlinearity of carbon cycle feedbacks. J. Clim., 24(16): , Aug doi: /2011jcli

13 Century-by-Century Carbon & Temperature Changes Time (year) Variable [CO 2 ] A (ppm) Time Period (years) Variable T2 m (K) T2 m (K) T2 m (K) CO (Pg C) CO (Pg C) CO (Pg C) CL (Pg C) CL (Pg C) CL (Pg C) EC (Pg C) EC (Pg C) EC (Pg C)

14 Climate Carbon Cycle Feedback Parameters and Gains Time Period (years) Parameter α (K ppm 1 ) βo (Pg C ppm 1 ) β O (Pg C ppm 1 ) βl (Pg C ppm 1 ) β L (Pg C ppm 1 ) γo (Pg C K 1 ) γ O (Pg C K 1 ) γl (Pg C K 1 ) γ L (Pg C K 1 ) g(β, γ ) g(β, γ ) g(β, γ ) g(β, γ ) g(e C, EC )