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 0.3C decade1 in this area during the period

19832006 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 m2 to 34.8 W m2, with a mean annual value of

19.8 W m2. 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 empiric research

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.