Fred Pearce writes:

The world is awash with greenhouses growing fresh vegetables year-round for health-conscious urbanites. There are so many of them that in places their plastic and glass roofs are reflecting sufficient solar radiation to cool local temperatures — even as surrounding areas warm due to climate change.

The extent of this accidental climate engineering is becoming ever more apparent as analysis of satellite images dramatically increases estimates of the area of the planet swathed in greenhouses. From southern Spain to northeast China and the Rift Valley in East Africa to Mexico, millions of acres of former scrub and marginal farmland are being replaced by glistening reflective surfaces.

The intensive agricultural methods employed within greenhouses may often damage local environments by overtaxing water supplies and polluting rivers and soils with nutrients, pesticides, and plastic waste. But the influence of these seas of plastic on local temperatures can be even more dramatic — and often beneficial. They increase the albedo, or reflectivity, of the land surface, typically by around a tenth, and so reduce solar heating of the lower atmosphere.

The extent of the planet’s growing enthusiasm for greenhouses was revealed in May by a new satellite mapping exercise, which estimated the land area covered with permanent greenhouses at 3.2 million acres, an area the size of Connecticut, with China hosting more than half of this expanse. This is more than twice previous estimates, and 40 times those made four decades ago. [Continue reading…]