But in order to save the climate it would be advised to first chop down that dark pine forest.

In our series geoengineering the world, we take a look at the globe at our desk and investigate all the places for which scientists have geoengineering ‘plans’ [everything is theory] in mind. After the Pacific, Greenland and the stratosphere, today we pay special attention to that piece of cropland down the road – because potentially any big surface with a colour can be geoengineered.

That is what researchers from the University of Bristol must have had in mind with their 2009 study, ‘Assessing the benefits of crop albedo bio-geoengineering‘, which we found in Environmental Research Letters. It should be relevant: combine all the acres and cropland adds up to 10 percent of the Earth’s surface.

Farmers with an interest in geoengineering and a will to contribute to cooling the planet should try and optimise their scheme taking the seasons into account:

Using a Hadley Centre climate model the researchers find crop canopy albedo – that is the reflectivity of an acre of say maize or potato plants viewed from above – is in higher latitudes, like Europe, the US, Canada, to be most relevant in summer as sun intensity is highest then. Further south, for instance in India, the opposite goes, as surface albedo is there much more relevant during the dry season than during the monsoon, which is generally clouded.

The researchers call their approach ‘bio-geoengineering’ and think, although global effects may be small, that it may be useful in regulating unwanted local climatic extremes.

All about the radiative balance

Citing older albedo studies the group states woodland [although of course an important carbon storage and an important driver to hydrological cycles] is unfavourable from a ‘solar radiation management’ perspective. Deciduous forests in the temperate climate zone have an average albedo of 0.18. Coniferous forests are slightly worse with an albedo of 0.16, reflecting just 16% of incoming solar radiation – and absorbing the rest, thereby ‘creating heat’.

Agricultural crops are usually lighter-coloured on average. Barley is cited as having an albedo of 0.23 around the temperate zone and sugar beet, with its broad leaves, would even reflect 26 percent of solar radiation.

Higher albedo varieties

Instead of advocating switching from crop type the researchers state lighter varieties per crop type deserve special attention. Albedo differences between different subspecies of wheat would be as high as 16 percent. Lighter crop varieties could bring additional benefits, as these tend to have greater water use efficiency and reduced leaf heating, potentially increasing agricultural productivity, and could therefore fit in climate adaptation programs as well.

In creating the lighter varieties the researchers do not rule out GMO may have a role to play.

Possible temperature effects

The model results show implementation could – in case of doubled CO2, and 3 ºC warming [IPCC AR4 climate sensitivity] – lead to 0.1 ºC cooling globally. Locally and seasonally the effect can be much larger. During the northern hemisphere summer months the introduction of increased crop canopy albedo with lighter varieties reduced local temperatures in these regions by 0.5 to 2 ºC. Effectiveness of crop albedo bio-geoengineering seems highest in Western Europe.

In South Asia the crop albedo increases could lead to a maximum cooling of 1 degree in spring, just before the onset of the rainy season, perhaps tempering the monsoon.

Crop yield

During European summer, the higher albedo crops would help keep soil moisture at relatively high levels. This could be beneficial to agricultural productivity, while the current climate trends, with increasing temperature and swift drying-out during the crucial first phase of the summer has detrimental effects on European agriculture.

© Rolf Schuttenhelm | www.bitsofscience.org