Andy Revkin alerted us to a new, quite interesting paper on the role of land use and land cover change on the global climate system.
The new paper is
George A Ban-Weiss, Govindasamy Bala, Long Cao, Julia Pongratz and Ken Caldeira 2011 Climate forcing and response to idealized changes in surface latent and sensible heat 2011 *Environ. Res. Lett.* *6* 034032 (doi: 10.1088/1748-9326/6/3/034032)
The abstract reads [highlight added]
Land use and land cover changes affect the partitioning of latent and sensible heat, which impacts the broader climate system. Increased latent heat flux to the atmosphere has a local cooling influence known as ‘evaporative cooling’, but this energy will be released back to the atmosphere wherever the water condenses. However, the extent to which local evaporative cooling provides a global cooling influence has not been well characterized. Here, we perform a highly idealized set of climate model simulations aimed at understanding the effects that changes in the balance between surface sensible and latent heating have on the global climate system. We find that globally adding a uniform 1 W m−2 source of latent heat flux along with a uniform 1 W m−2 sink of sensible heat leads to a decrease in global mean surface air temperature of 0.54 ± 0.04 K. This occurs largely as a consequence of planetary albedo increases associated with an increase in low elevation cloudiness caused by increased evaporation. Thus, our model results indicate that, on average, when latent heating replaces sensible heating, global, and not merely local, surface temperatures decrease.
Their study approach includes the text
The model used in this study is the NCAR Community Atmosphere Model (CAM3.1) (Collins et al 2004) coupled to the Community Land Model (CLM3.0) (Oleson et al 2004) and a slab ocean model. The configuration used in this study has a finite-volume dynamical core and 2◦ × 2.5◦ (longitude × latitude) grid resolution. CAM3.1 has 26 horizontal layers. All simulations were run with a prescribed atmospheric CO2 concentration of 390 ppm, which is the approximate current level.
Simulating stationary climates. For each case (i.e. control, ↑L↓S, ↑L, and ↓S), we performed an ensemble of three 20-year simulations and then let one ensemble member of each case run for 100 model years. The global climate model used approaches stationarity within 30 years; ‘total responses’ are reported for means of the last 70 years of the 100-year simulations, representing a near-stationary climate state.
The conclusion starts with
Changes in land cover alter the partitioning of latent and sensible heat fluxes. Surface latent heat flux increases are expected from e.g. reforestation (e.g. Anderson et al 2011) and/or irrigation (e.g. Boucher et al 2004, Lobell et al 2006, 2009)
and ends with
This study points to the need for improved understanding between changes at Earth’s surface, and how they interact with fluxes at the top of the atmosphere to drive regional and global climate change.
This paper is an original investigation of the role of land use and land cover change on the climate system. We have been proposing for years that the IPCC move towards a broader assessment of the role of humans on the climate. This includes assessment reports (essentially ignored in the 2007 IPCC WG1 report); i.e.
Kabat, P., Claussen, M., Dirmeyer, P.A., J.H.C. Gash, L. Bravo de Guenni, M. Meybeck, R.A. Pielke Sr., C.J. Vorosmarty, R.W.A. Hutjes, and S. Lutkemeier, Editors, 2004: Vegetation, water, humans and the climate: A new perspective on an interactive system. Springer, Berlin, Global Change – The IGBP Series, 566 pp
National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp
and a wide range of research papers; e.g.
Pielke Sr., R.A., G. Marland, R.A. Betts, T.N. Chase, J.L. Eastman, J.O. Niles, D. Niyogi, and S. Running, 2002: The influence of land-use change and landscape dynamics on the climate system- relevance to climate change policy beyond the radiative effect of greenhouse gases. Phil. Trans. A. Special Theme Issue, 360, 1705-1719.
Chase, T.N., R.A. Pielke, T.G.F. Kittel, R.R. Nemani, and S.W. Running, 2000: Simulated impacts of historical land cover changes on global climate in northern winter. Climate Dynamics, 16, 93-105.
Pielke Sr., R.A., 2001: Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Rev. Geophys., 39, 151-177.
More recent papers include
McAlpine, C.A., W.F. Laurance, J.G. Ryan, L. Seabrook, J.I. Syktus, A.E. Etter, P.M. Fearnside, P. Dargusch, and R.A. Pielke Sr. 2010: More than CO2: A broader picture for managing climate change and variability to avoid ecosystem collapse. Current Opinion in Environmental Sustainability, 2:334-336, DOI10.1016/j.cosust.2010.10.001.
Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.
We also have a new paper that was just accepted for publication (and we will update the url of it on my research website in the next few days) that complements the new Ban-Weiss et al 2011 article;
Pielke Sr., R.A., A. Pitman, D. Niyogi, R. Mahmood, C. McAlpine, F. Hossain, Kees Klein 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. Wiley Interdisciplinary Reviews: Climate Change, Invited paper, in press.
The Ban-Weiss et al paper is a much-needed perspective on the role of land use and land cover change as a first-order human climate forcing.