New Paper “Simulating The Biogeochemical And Biogeophysical Impacts Of Transient Land Cover Change And Wood Harvest In The Community Climate System Model (CCSM4) From 1850 to 2100″ By Lawrence Et Al 2012

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There is a new global model sensitivity study of the role of land surface processes on the climate system [h/t Rezaul Mahmood]. The new paper is

Lawrence, Peter J., and Coauthors, 2012: Simulating the Biogeochemical and Biogeophysical Impacts of Transient Land Cover Change and Wood Harvest in the Community Climate System Model (CCSM4) from 1850 to 2100. J. Climate, 25, 3071–3095. doi: http://dx.doi.org/10.1175/JCLI-D-11-00256.1

While this paper continues the presentation of time periods in the future (out to 2100) when the CCSM4 has not demonstrated skill at prediction of historical changes in biogeochemical and biogeophysical impacts (i.e. hincast runs), the paper, nevertheless, is an interesting new model sensitivity study. It provides further evidence of the importance of land surface processes within the climate system, as we summarized recently in our paper

Pielke Sr., R.A., A. Pitman, D. Niyogi, R. Mahmood, C. McAlpine, F. Hossain, K. Goldewijk, U. Nair, R. Betts, S. Fall, M. Reichstein, P. Kabat, and N. de Noblet-Ducoudré, 2011: Land  use/land cover changes and climate: Modeling analysis  and  observational evidence. WIREs Clim Change 2011, 2:828–850. doi: 10.1002/wcc.144.

The abstract of the Lawrence et al 2012 paper reads [highlight added]

To assess the climate impacts of historical and projected land cover change in the Community Climate System Model, version 4 (CCSM4), new time series of transient Community Land Model, version 4 (CLM4) plant functional type (PFT) and wood harvest parameters have been developed. The new parameters capture the dynamics of the Coupled Model Intercomparison Project phase 5 (CMIP5) land cover change and wood harvest trajectories for the historical period from 1850 to 2005 and for the four representative concentration pathway (RCP) scenarios from 2006 to 2100. Analysis of the biogeochemical impacts of land cover change in CCSM4 reveals that the model produced a historical cumulative land use flux of 127.7 PgC from 1850 to 2005, which is in general agreement with other global estimates of 156 PgC for the same period. The biogeophysical impacts of the transient land cover change parameters were cooling of the near-surface atmosphere over land by −0.1°C, through increased surface albedo and reduced shortwave radiation absorption. When combined with other transient climate forcings, the higher albedo from land cover change was counteracted by decreasing snow albedo from black carbon deposition and high-latitude warming. The future CCSM4 RCP simulations showed that the CLM4 transient PFT parameters can be used to represent a wide range of land cover change scenarios. In the reforestation scenario of RCP 4.5, CCSM4 simulated a drawdown of 67.3 PgC from the atmosphere into the terrestrial ecosystem and product pools. By contrast the RCP 8.5 scenario with deforestation and high wood harvest resulted in the release of 30.3 PgC currently stored in the ecosystem.

The paper starts with the text

Recent studies have shown that historical human land use and land cover change have significantly impacted the earth’s climate through changes in the carbon cycle, through altered biogeochemical processes (Houghton 2003; Canadell et al. 2007; Bonan 2008; Shevliakova et al. 2009) and through changes in energy and moisture fluxes to the atmosphere, by altering biogeophysical processes (Betts et al. 2001; Feddema et al. 2005; Findell et al. 2007; Bala et al. 2007; Lawrence and Chase 2010).

The evidence that land surface process (both as a climate forcing and as a feedback) are at least as important as other climate forcings, including from the radiative effect of added CO2, are overwhelming, and must be part of an objective assessment of the climate system, as influenced by humans.  

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