NewScientist, October 10, 2008

HERE is one greenhouse effect that is welcome: the roofs of hothouse farms in Spain reflect so much sunlight that they may be pushing down local temperatures.

Since the 1970s, semi-arid pasture land in Almeria, south-eastern Spain, has been replaced by greenhouse horticulture. Today, Almeria has the largest expanse of greenhouses in the world - around 26,000 hectares.

Pablo Campra of the University of Almeria and colleagues studied temperature trends from weather stations inside the region, and from other areas of Spain. With the help of satellite data they compared semi-arid pasture land and greenhouses, looking for differences in surface radiation and albedo -- the ability to reflect sunlight.

In the greenhouse region, air temperature has cooled by an average of 0.3 °C per decade since 1983. In the rest of Spain it has risen by around 0.5 °C. The satellite data revealed that the white greenhouses were much more reflective than farmland. (Journal of Geophysical Research, DOI: 10.1029/2008JD009912).

The team thinks that the white roofs are key to the cooling, demonstrating the potential for placing reflective surfaces in semi-arid regions of the world to offset climate change.

Link to article: http://environment.newscientist.com/article/mg20026775.000