Now that it is becoming increasingly clear that we are already on board for a substantial increase in global temperature in the coming century, the discussion has broadened from efforts to cut the greenhouse gases that drive the process, which are obviously more critical than ever, to include also efforts to mitigate the expected impacts.
In addition to efforts at reducing greenhouse gas emissions and overhauling energy industries, there have been many suggestions for geo-engineering on a global scale to reduce atmospheric heating. The latter range from the sublime to (often) the ridiculous — huge parasols in space to shade the earth, dumping freight cars of iron filings into the tropical ocean to stimulate blooms of plankton that suck down the CO2, etc. Many such suggestions would be astronomically expensive and some are truly over the top.
Is there really no better way? Why not look to Nature for an answer? This approach has worked countless times before. Natural ecosystems have had 3-some-odd-billion years to experiment in the face of constant pressure and have discovered a plethora of ingenious ways to solve problems.
Consider the new paper in Current Biology by Ridgwell and colleagues. These authors suggest the ingenious hypothesis that regional warming might be mitigated not by costly futuristic infrastructure but by relatively simple changes in crop varieties that change leaf albedo over large areas.
Ridgwell et al. proceed from the observation that historical conversion of native vegetation to crops with higher albedo (i.e., ability to reflect incoming solar radiation) has reduced warming, and they suggest a low-tech, relatively inexpensive approach that would exploit the existing infrastructure of agriculture. The idea is to switch crops to known varieties that have leaf glossiness and/or canopy architecture that reflect more solar radiation. By making these changes in the Hadley Centre coupled atmosphere-ocean model, they estimate that summer temperatures could be reduced by a substantial 1 degree C throughout much of the mid-latitude northern hemisphere. These changes could potentially be done cheaply and quickly and might even be improved by selective breeding for higher-albedo foliage.
The figure at left shows the global distribution of croplands. The model of Ridgwell et al. allowed C3 grasses (crops such as rice, wheat, and soybeans) and C4 grasses (e.g., maize, sorghum, sugarcane, and millet) to grow within these areas designated as cropland.
The figure below shows the results in terms of climatic impacts of bio-geoengineering. The colors show the global anomalies of summer (JJA) and winter (DJF) surface air temperature resulting from a +0.04 increase in maximum crop canopy albedo and an elevated atmospheric CO2 concentration of 700 ppm, relative to “control” conditions with no change in crop albedo. The small “hotspots” of cooling or warming visible on the map are mostly associated with localized changes in seasonal sea-ice extent or snow cover relative to the control, induced by the cropland albedo changes elsewhere.
To me this is a classic potential application of reconciliation ecology, and also biomimicry, that is creative use of nature’s methods to achieve goals that are important to humanity but minimize impacts on the rest of the ecosystem (in the sense that we already have huge areas under agricultural cultivation and this is unlikely to change). Plus it’s surely a whole lot cheaper than putting a bunch of colossal umbrellas in space, even if that was likely to work.