A new paper has been accepted which further supports the conclusions 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. doi: 10.1002/wcc.144
The new paper is
de Noblet-Ducoudré, N., J-P. Boisier, A.J. Pitman, G.B. Bonan, V. Brovkin, F. Cruz, C. Delire, V. Gayler, B.J.J.M. van den Hurk, P.J. Lawrence, M.K. van der Molen, C. Müller, C.H. Reick, B.J. Strengers, and A. Voldoire, Determining robust impacts of land-use induced land-cover changes on surface climate over North America and Eurasia; Results from the first set of LUCID experiments, J. Climate, accepted 9th November, 2011.
The abstract reads [highlight added]
The project LUCID was conceived to address the robustness of biogeophysical impacts of historical land-use induced land cover changes (LULCC). LUCID used seven atmosphere land models with a common experimental design to explore those impacts of LULCC that are robust and consistent across the climate models. The biogeophysical impacts of LULCC were also compared to the impact of elevated greenhouse gases and resulting changes in sea surface temperatures and sea-ice extent (CO2SST). Focussing our analysis on Eurasia and North America, we show that LULCC has, on a number of variables, an impact of similar magnitude but of an opposite sign, to increased greenhouse gases and warmer oceans. However, the variability among the individual models’ response to LULCC is larger than that found from the increase in CO2SST. Our results show that although the dispersion among the models’ response to LULCC is large, there are a number of robust common features shared by all models: the amount of available energy used for turbulent fluxes is consistent between the models, and the changes in response to LULCC depend almost linearly on the amount of trees removed. However, less encouraging is the conclusion that there is no consistency among the various models regarding how LULCC affects the partitioning of available energy between latent and sensible heat fluxes at a specific time period. Our results therefore highlight the urgent need to evaluate land surface models more thoroughly, in particular in how they respond to a perturbation in addition to how they simulate an observed average state.
The conclusion includes the text
Increased concentration of greenhouse gases in the atmosphere, and the subsequent changes in sea-surface temperatures and sea-ice extent, are often used as the main drivers of climate change also over land. Our results suggest that such an assumption leads to erroneous conclusions regarding the land-surface impacts of climate change in regions where LULCC has been significant. LULCC affects a number of variables to a similar magnitude, but of opposite sign, to increasing greenhouse gas concentrations. LULCC therefore has the potential to mask a regional warming signal with the resulting risk that detection and attribution studies may miss a clear greenhouse signal or mis-attribute a greenhouse signal if LULCC is poorly accounted for. Detection and attribution is a complex process that is beyond the scope of this paper (see for example Stott et al. 2010). However, our results suggest that including LULCC could improve the regional scale detection of the impacts of specific forcings by ensuring that land cover’s contribution to any regional changes is appropriately represented. LULCC will suppress the impacts of, for example, increasing CO2 in some regions that cool due to land cover change, and amplify the impacts of increasing CO2 in regions that warm due to land cover change. In the former case, this risks missing the detection of a CO2 signal, while in the latter it risks a false-positive detection of a CO2 signal. Aerosols, which typically cool, particularly strongly at regional scales, are an additional forcing that might be masked by the mis-representation of LULCC.
Our findings argue for the inclusion of LULCC in climate projections, as now in process for the CMIP5 simulations (e.g., Arora et al., GRL, 2011). However, we have also shown that the differences among the seven models’ response to LULCC is larger than the differences that results from the change in CO2SST. Since LULCC is implemented in most CMIP5 models, we expect a larger divergence among climate models in comparison to earlier efforts over regions of intense LULCC coincident with dense human populations. This problem will only be resolved via a more systematic effort within the climate modelling and land surface modelling communities starting with a coordinated evaluation of how to represent LULCC, how well models capture the impacts of LULCC in both off-line and coupled simulations.