By carefully selecting which varieties of food crops to cultivate, much of Europe and North America could be cooled by up to 1°C during the summer growing season, say researchers from the University of Bristol, UK. This is equivalent to an annual global cooling of over 0.1°C, almost 20% of the total global temperature increase since the Industrial Revolution.
The growing of crops already produces a cooling of the climate because they reflect more sunlight back into space, compared with natural vegetation. Different varieties of the same crop vary significantly in their solar reflectivity (called ‘albedo’), so selecting varieties that are more reflective will enhance this cooling effect. Since arable agriculture is a global industry, such cooling could be extensive.
Dr Andy Ridgwell and colleagues at the University of Bristol argue that we should select crop varieties in order to exert a control on the climate, in the same way that we currently cultivate specific varieties to maximize and fine-tune food production.
Dr Ridgwell said: “We have evaluated the effect of our approach in a global climate model. By choosing from among current crop varieties, our best estimate for how much reflectivity might be increased leads us to predict that summer-time temperatures could be reduced by more than 1°C throughout much of central North America and mid-latitude Eurasia. Ultimately, further regional cooling of the climate could be made through selective breeding or genetic modification to optimise crop plant albedo.”
The team emphasised that unlike growing biofuels, such a plan could be achieved without disrupting food production, either in terms of yield or the types of crops grown. “We propose choosing between different varieties of the same crop species in order to maximize solar reflectivity rather than changing crop type, although the latter could also produce climatic benefits,” explained Ridgwell.
Over the next hundred years, making these kinds of decisions would be equivalent to averting the carbon footprint of 195 billion tonnes of CO2 emitted into the atmosphere. Farmers could be encouraged to grow such crops by issuing them with carbon credits. Ridgwell has calculated that if such a mechanism were in place farmers might expect to earn in the region of 23 euros per hectare per year for the warming averted. Biofuels currently earn 45 euros per hectare per year, but take up valuable agricultural land needed for growing crops.