Comments
Surface Temperature Cooling due to Land Use Change
Another paper has been published which demonstrates how land use change can have a bigger effect on climate locally than the claimed influence of increased greenhouse gasses in the atmosphere. The paper is:
Campra, P., M. Garcia, Y. Canton, and A. Palacios-Orueta, 2008: Surface temperature cooling trends and negative radiative forcing due to land use change toward greenhouse farming in southeastern Spain,J. Geophys. Res., 113, D18109, doi:10.1029/2008JD009912.
The abstract reads
“Greenhouse horticulture has experienced in recent decades a dramatic spatial expansion in the semiarid province of Almeria, in southeastern (SE) Spain, reaching a continuous area of 26,000 ha in 2007, the widest greenhouse area in the world. A significant surface air temperature trend of −0.3°C decade−1in this area during the period 1983–2006 is first time reported here. This local cooling trend shows no correlation with Spanish regional and global warming trends. Radiative forcing (RF) is widely used to assess and compare the climate change mechanisms. Surface shortwave RF (SWRF) caused through clearing of pasture land for greenhouse farming development in this area is estimated here. We present the first empirical evidences to support the working hypothesis of the development of a localized forcing created by surface albedo change to explain the differences in temperature trends among stations either inside or far from this agricultural land. SWRF was estimated from satellite-retrieved surface albedo data and calculated shortwave outgoing fluxes associated with either uses of land under typical incoming solar radiation. Outgoing fluxes were calculated from Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data. A difference in mean annual surface albedo of +0.09 was measured comparing greenhouses surface to a typical pasture land. Strong negative forcing associated with land use change was estimated all year round, ranging from −5.0 W m−2 to −34.8 W m−2, with a mean annual value of −19.8 W m−2. According to our data of SWRF and local temperatures trends, recent development of greenhouse horticulture in this area may have masked local warming signals associated to greenhouse gases increase.”
The introduction reads in part
“Anthropogenic changes to the physical properties of the land surface can perturb the climate by altering the Earth’s radiative energy balance, and have been regarded as a cause of regional and even global climate change [Sagan et al., 1979]. Furthermore, land use changes are likely to be among the first drivers of climate change at meso- and local scales. Surface albedo affects the shortwave radiation budget by controlling how much incoming solar radiation is absorbed by the surface. Because of this, changes in surface albedo have been suspected of being the dominant influence of mid- and high-latitude land use change on climate [Betts, 2001]. Small changes in Earth’s albedo, even below satellite detection limits, can lead to global temperature changes equivalent to those associated with increase in greenhouse gases [Charlson et al., 2005].”
The conclusion has the text
“Our results show that, at local and meso-scale, greenhouse farming is very likely the most powerful driver of climate change in the area of study, probably due to the dramatic increase in surface albedo of the highly reflective plastic cover over a widespread agricultural area, which largely offsets positive forcing (+2 W m−2) very probably induced by global increase in greenhouse gases [Forster et al., 2007]. The main general implication of these findings is to highlight the importance of human development of high albedo surfaces in the strategies of mitigation and adaptation to global warming at local scale. However control stations records outside the GH area show that little or no effects on surface temperature extend far from the high albedo area, so the forcing caused by greenhouse development seems to be very localized.”
and
“The relative influence on local climate of other physical changes must be explored. The land use climate forcing that we have estimated here does not fully represent GH land use effects, as there are other changes in surface properties affecting the surface energy balance that have not been considered. For instance, eco-physiological and aerodynamic changes and alterations of roughness still remain undetermined. The complex role of evapotranspiration associated to this drip-irrigated soil under a plastic cover must be investigated [Fernandez et al., 2007]. Cooling effect of higher albedo could have been enhanced by the increase in latent heat flux derived from irrigation within the greenhouses (released as water vapor by greenhouses ventilation), with respect to previous pasture cover, further reducing sensible heat transfer and surface air temperature. On the contrary, irrigation might also cause a positive forcing by the increase in water vapor in the lower atmosphere [Boucher et al., 2004; Christy et al., 2006].”
The paper concludes with the text
“Even the RF [Radiative Forcing] concept might not be the most appropriate concept in our case, so that other alternative metrics [Pielke et al., 2002] could be advisable to estimate and model the net impact on the local climate of GH development.”
This paper provides further support for the viewpoint presented in
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.
where it is written that
“Regional variations in radiative forcing may have important regional and global climatic implications that are not resolved by the concept of global mean radiative forcing.”
and
“Several types of forcings—most notably aerosols, land-use and land-cover change, and modifications to biogeochemistry—impact the climate system in nonradiative ways, in particular by modifying the hydrological cycle and vegetation dynamics.”
Reports such as the 2007 IPCC and the 2008 CCSP assessments are ignoring this peer reviewed issue. Poor policy decisions are being made because the concept of how humans are altering the climate system has not been properly communicated to the policymakers. This is a failure of the IPCC and CCSP process.
Post reproduced from Roger Pielke Sr’s Climate Science weblog.
October 16th, 2008 at 4:09 am
Very interesting point I had not considered before this…