Crop selection could help cool Europe and North America in summertime
Scientists in the UK have proposed an 'albedo bio-geoengineering' approach to slowing down the warming of the Earth's surface, whereby agricultural crop varieties would be specifically chosen to maximise their solar reflectivity. The study, published in the journal Current Biology, demonstrates how such low-cost measures could cool much of Europe and North America by up to 1°C during the summer growing season. Increasing greenhouse-gas emissions are leading to a potentially unmanageable level of climate change, and this has spurred the search for global technological solutions referred to as 'geoengineering'. While there is no substitute for CO2 emission reduction, complementary efforts to combat global warming are being actively sought. However, such efforts typically call for costly new infrastructures or industries, making them a tough sell. In the current study, scientists carried out a suite of climate-model-sensitivity experiments in an effort to see how simple crop modifications might affect global climate conditions. They reasoned that because agricultural crops are more reflective than natural vegetation, due to their glossier leaves and wider canopies, these traits could be further exploited to reflect still more of the sun's heat back into space. They call this climate-change mitigation approach 'albedo bio-geoengineering'. The reflectivity of plants, called 'albedo', varies between varieties of the same plant species. For example, the albedo of one type of sorghum is 0.16 times higher than another simply because of the wax structure in the leaves. At the same time, albedo between varieties of maize can vary widely simply because of differences in leaf shape, or canopy. The scientists used a computer model to test the effects of increasing crop reflectivity by 0.04. The model took ocean and atmosphere circulation, sea-ice and terrestrial vegetation into account; its land-surface scheme predicted soil moisture, productivity and energy exchange with the atmosphere over 200 years. After a 50-year adjustment period, they started to see some interesting results. '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,' explained Dr Andy Ridgwell of the University of Bristol. 'Ultimately, further regional cooling of the climate could be made through selective breeding or genetic modification to optimise crop plant albedo.' The researchers also note that using reflective sprays on crop leaves did not affect yield. Growing biofuels has been seen as a way to achieve a similar effect. However, this practice disrupts food production, which is increasingly important as the world's population grows. The bio-geoengineering approach, the researchers say, could achieve beneficial effects 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 maximise solar reflectivity rather than changing crop type, although the latter could also produce climatic benefits,' said Dr Ridgwell. Over the next 100 years, these simple decisions could go a long way to reducing the warming of the Earth's surface. It is important to consider the inherently regional (and seasonal) climate effects that would be seen by modifying crop properties. According to Dr Ridgwell, further research into the variability in albedo between the different strains of common crop plants is necessary. Additionally, bio-geoengineering of croplands should be considered in conjunction with other geoengineering schemes such as the whitening of built structures or changes to pasture plants. The reduction demonstrated by the study is equivalent to an annual global cooling of over 0.1°C. 'Overall, bio-geoengineering could fulfil a role as a temporary measure for reducing the severity of agricultural and health impacts of heat waves in the industrialised north,' the study concludes. However, the authors caution that, 'on a global scale, it has limited effectiveness for the mitigation of future climate change and cannot substitute for CO2 emission reduction.'
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