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.'

For more information, please visit:

University of Bristol:
[www.bris.ac.uk]
&
www.checkbiotech.org