Comment And Recommendation On Bill Ruddiman’s View Of Early Human Effects On Climate

Real Climate had an interesting post by Bill Rudiman on April 15 2011 titled

An Emerging View on Early Land Use

Excerpts from his post include [highlight added]

Historical data on land use extending back some 2000 years exists for two regions — Europe and China. In a 2009 paper, Jed Kaplan and colleagues reported evidence showing nearly complete deforestation in Europe at mid-range population densities, but very little additional clearance at higher densities. Embedded in this historical relationship was a trend from much greater per-capita clearance 2000 years ago to much smaller values in recent centuries. Similarly, a Holocene special-issue paper by Ruddiman and colleagues pointed to a pioneering study of early agriculture in China published in 1937 by J. L. Buck. Paired with reasonably well-constrained population estimates that extend back to the Han dynasty 2000 years ago, these data show a 4-fold decrease in per-capita land area cultivated in China from that time until the 1800′s.”

and

“……an in-press paper by Fuller and colleagues on ‘The contribution of rice agriculture and livestock pastoralism to prehistoric methane levels: an archeological assessment’ assembled archeological evidence from hundreds of well-dated sites showing the spread of irrigated rice across southern Asia between 5000 and 1000 years ago. Based on modern regional relationships, they assumed that rice farming in each region subsequently filled in with the log of population density. Combining the first arrival of rice and the subsequent infilling, Fuller and colleagues projected the progressive increase in the total area of southern Asia devoted to irrigated rice.

Their estimate showed a rising exponential trend in total area that reached more than 35% of the modern value by 1000 years ago, even though the population in the rice-growing areas of Asia at that time was only 5-6% of modern levels. This mismatch again indicates much greater per-capita land use early in the historical era than in later pre-industrial time.”

This recognition of major human landscape change thousands of years ago documents yet again why we need a broader perspective of its role within the climate system.

However, what is very puzzling about Ruddiman’s post is that he does not discuss the role of concurrent effects on the water and energy fluxes and effects on weather and other aspects of climate.  This includes the regional change in surface albedo, but also the effects on the net radiation received at the surface and its partitioning between sensible and latent heat fluxes. This need to consider the water and energy effects of landscape change on climate, in addition to the effects on the carbon,  and other trace constituent budgets, is discussed, as just a few examples, in

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.

Pielke, R.A. Sr., J. Adegoke, A. Beltran-Przekurat, C.A. Hiemstra, J. Lin, U.S. Nair, D. Niyogi, and T.E. Nobis, 2007: An overview of regional land use and land cover impacts on rainfall. Tellus B, 59, 587-601.

and

Mahmood, R., R.A. Pielke Sr., K.G. Hubbard, D. Niyogi, G. Bonan, P. Lawrence, B. Baker, R. McNider, C. McAlpine, A. Etter, S. Gameda, B. Qian, A. Carleton, A. Beltran-Przekurat, T. Chase, A.I. Quintanar, J.O. Adegoke, S. Vezhapparambu, G. Conner, S. Asefi, E. Sertel, D.R. Legates, Y. Wu, R. Hale, O.W. Frauenfeld, A. Watts, M. Shepherd, C. Mitra, V.G. Anantharaj, S. Fall,R. Lund, A. Nordfelt, P. Blanken, J. Du, H.-I. Chang, R. Leeper, U.S. Nair, S. Dobler, R. Deo, and J. Syktus, 2010: Impacts of land use land cover change on climate and future research priorities. Bull. Amer. Meteor. Soc., 91, 37–46, DOI: 10.1175/2009BAMS2769.1

The abstract of the Pielke 2001 paper reads

“This paper uses published work to demonstrate the link between surface moisture and heat fluxes and cumulus convective rainfall. The Earth’s surface role with respect to the surface energy and moisture budgets is examined. Changes in land surface properties are shown to influence the heat and moisture fluxes within the planetary boundary layer, convective available potential energy, and other measures of the deep cumulus cloud activity. The spatial structure of the surface heating, as influenced by landscape patterning, produces focused regions for deep cumulonimbus convection. In the tropics, and during midlatitude summers, deep cumulus convection has apparently been significantly altered as a result of landscape changes. These alterations in cumulus convection teleconnect to higher latitudes, which significantly alters the weather in those regions. The effect of tropical deforestation is most clearly defined in the winter hemisphere. In the context of climate, landscape processes are shown to be as much a part the climate system as are atmospheric processes.”

The Ruddiman analysis needs to be extended to include other effects of early landscape conversion besides that of the  greenhouse gas radiative effects.

source of image – Deforestation in Yunnan Province, China

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