Abstract
Polar amplification of surface warming has previously been displayed by one of the authors in a simplified climate system model with no ice-albedo feedbacks. A physical mechanism responsible for this pattern is presented and tested in an energy balance model and two different GCMs through a series of fixed-SST and “ghost forcing” experiments. In the first ghost forcing experiment, 4 W/m2 is added uniformly to the mixed layer heat budget and in the second and third, the same forcing is confined to the tropics and extra-tropics, respectively. The result of the uniform forcing is a polar amplified response much like that resulting from a doubling of CO2. Due to an observed linearity this response can be interpreted as the sum of the essentially uniform response to the tropical-only forcing and a more localized response to the extra-tropical-only forcing. The flat response to the tropical forcing comes about due to increased meridional heat transports leading to a warming and moistening of the high-latitude atmosphere. This produces a longwave forcing on the high-latitude surface budget which also has been observed by other investigators. Moreover, the tropical surface budget is found to be more sensitive to SST changes than the extra-tropical surface budget. This strengthens the tendency for the above mechanism to produce polar amplification, since the tropics need to warm less to counter an imposed forcing.
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References
Alexeev VA (2003) Sensitivity to CO2 doubling of an atmospheric GCM coupled to an oceanic mixed layer: a linear analysis. Clim Dyn 20:775–787
Alexeev VA, Bates JR (1999) GCM experiments to test a proposed dynamical stabilizing mechanism in the climate system. Tellus 51A:630–651
Bates JR (1999) A dynamical stabilizer in the climate system: a mechanism suggested by a simple model. Tellus 51A:349–372
Bates JR (2003) On climate stability, climate sensitivity and the dynamics of the enhanced greenhouse effect. DCESS Report No.3, available from Department of Geophysics, University of Copenhagen http://www.dclimate.gfy.ku.dk
Bellon G, Le Treut H, Ghil M (2003) Large-scale and evaporation-wind feedbacks in a box model of the tropical climate. Geophys Res Lett 30(22, Art. no. 2145)
Caballero R, Langen PL (2005) The dynamic range of poleward energy transport in an atmospheric general circulation model. Geophys Res Lett 32:L02705. DOI: 10.1029/2004GL021581
Chen D, Gerdes R, Lohmann G (1995) A 1-d atmospheric energy balance model developed for ocean modeling. Theor Appl Climatol 51:25–38
Covey C, AchutaRao KM, Cubasch U, Jones P, Lambert SJ, Mann ME, Phillips TJ, Taylor KE (2003) An overview of results from the Coupled Model Intercomparison Project. Glob Planet Change 37:103–133
Flato GM, Hibler WD (1992) Modeling pack ice as a cavitating fluid. J Phys Oc 22:626–651
Hall A (2004) The role of surface albedo feedback in climate. J Clim 17:1550–1568
Hansen J, Sato M, Ruedy R (1997) Radiative forcing and climate response. J Geophys Res 102(D6):6831–6864
Hartmann DL (1994) Global physical climatology. Academic, New York
Hibler WD (1985) Modeling sea-ice dynamics. Adv Geophys 28:549–579
Houghton JT et al (eds) (2001) IPCC, Climate: the scientific basis. Cambridge University Press, Cambridge
Kiehl JT, Hack JJ, Bonan GB, Boville BA, Briegleb BP, Williamson DL, Rasch PJ (1996) Description of the NCAR Community Climate Model (CCM3). Technical Report TN-420, CGD, National Center for Atmospheric Research
Langen PL, Alexeev VA (2004) Multiple equilibria and asymmetric climates in the CCM3 coupled to an oceanic mixed layer with thermodynamic sea ice. Geophys Res Lett 31. DOI: 10.1029/2003GL019039
Manabe S, Stouffer RJ, Spelman MJ, Bryan K (1991) Transient responses of a coupled ocean–atmosphere model to gradual changes in atmospheric CO2. Part I: annual mean response. J Clim 4:785–818
Manabe S, Spelman MJ, Stouffer RJ (1992) Transient responses of a coupled ocean–atmosphere model to gradual changes in atmospheric CO2. Part II: seasonal response. J Clim 5:105–126
North GR (1975) Analytical solution to a simple climate model with diffusive heat transport. J Atmos Sci 32:1301–1307
Polyakov IV, Alekseev GV, Bekryaev RV, Bhatt U, Colony RL, Johnson MA, Karklin VP, Makshtas AP, Walsh D, Yulin AV (2002) Observationally based assessment of polar amplification of global warming. Geophys Res Lett 29(18):1878
Rodgers KB, Lohmann G, Lorenz S, Schneider R, Henderson GM (2003) A tropical mechanism for Northern Hemisphere deglaciation. Geochem Geophys Geosyst 4(5):1046. DOI:10.1029/2003GC000508
Sarachik ED (1978) Tropical sea surface temperature: an interactive one-dimensional atmosphere-ocean model. Dyn Atmos Oceans 2:455–469
Schneider EK, Lindzen RS, Kirtman BP (1997) A tropical influence on global climate. J Atm Sci 54:1349–1358
Schneider EK, Kirtman BP, Lindzen RS (1999) Tropospheric water vapor and climate sensitivity. J Atm Sci 56:1649–1658
Shine KP, Cook J, Highwood EJ, Joshi MM (2003) An alternative to radiative forcing for estimating the relative importance of climate change mechanisms. Geophys Res Lett 30(20), 2047. DOI:10.1029/2003GL018141
Sokolov AP, Stone PH (1998) A flexible climate model for use in integrated assessments. Clim Dyn 14:291–303
Vavrus SJ (2004) The impact of cloud feedbacks on arctic climate under greenhouse forcing. J Clim 17:603–615
Vavrus SJ, Harrison SP (2003) The impact of sea ice dynamics on the arctic climate system. Clim Dyn 20. DOI:10.1007/s00382–003–0309–5
Walsh JE, Kattsov VM, Chapman WL, Govorkova V, Pavlova T (2002) Comparison of arctic climate simulations by uncoupled and coupled global models. J Clim 15(12):1429–1446
Acknowledgements
The work was supported by IARC/NSF Cooperative Agreement 330360-66900 and the University of Copenhagen. The authors would like to thank R. Caballero for useful discussions, the CAM-user group for answering questions about the 1D CCM radiation model, and E. Schneider and an anonymous reviewer for suggestions and comments that have lead to significant improvements of the manuscript.
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Alexeev, V.A., Langen, P.L. & Bates, J.R. Polar amplification of surface warming on an aquaplanet in “ghost forcing” experiments without sea ice feedbacks. Climate Dynamics 24, 655–666 (2005). https://doi.org/10.1007/s00382-005-0018-3
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DOI: https://doi.org/10.1007/s00382-005-0018-3