Increasing Surface Albedo: Crops and Deserts

Bio-geoengineering vegetation

Rather than inventing new technology, scientists are considering the possibility of bio-geoengineering. It is known that different plants have different albedos (absorb a different percentage of energy), mainly because of their difference in morphology, canopy form and other inner properties. Therefore, we could select the crops with higher albedo and therefore increase total albedo of the Earth. 

But this can only be done in a small percentage of land, where there is no water, no deserts, and no urban cities. As a consequence, this seems like it would be a tiny difference, so the basic question is, would it make any difference? 

Ridgwell et al, 2009, ran a model to find out the answer to this question. They assumed a CO2 concentration of 700 ppm and compared the modelled Surface Air Anomaly for 700 ppm with no crop modifications vs 700 ppm with crop modifications. 

The results are shown in the following image. We can see that this method can bring a decrease of more than 1ºC in some areas of North America and Eurasia in summertime (JJA). However, in winter (DJF), no significant changes can be observed in these regions, mainly because the percentage of snow reduces the impact on any vegetation change, and also because of the reduced energy income.

It is worth mentioning the significant decrease in temperature that would exist in the Barent Sea, possibly improving sea-ice retreat.

Surface Air Temperature anomaly for 700ppm CO2 concentration and biogeoengineering according to Ridgwell et al (2009)

Desert reflectors

Deserts seem to be the ideal candidates for albedo modification, because of their vast extent, because they are mainly inhabited and because they are relatively useless (Gaskill, 2004). However, deserts are currently the second area with highest albedo (after ice) with a value of 0.36. Therefore increasing the albedo would be difficult. 

Gaskill proposed covering 4.5 of the total amount of 7.5 million squared miles of desert with a reflective surface, to increase albedo. This would increase the desert mean albedo from 0.36 to 0.8, and lead to a total net radiative forcing of -2.75 W/m2. 

We can see this amount is much more significant than the amount discussed by increasing urban albedo, or even increasing crops albedo, and is very close to the -4 W/m2 we discussed we ideally needed. 

Now, this is my personal opinion. However great the figure of net radiative forcing is, it is clear that this solution is in the ethic borderline to what a lot of people criticise about geoengineering, because we are "playing God" with planet Earth. This is an example where things could perfectly get out of control. The addition of a man made material to 10% of the total planet surface could have infinite chaotic secondary effects, either ecological, climate or others. Air circulation and sand circulation play important roles in the climate of the entire world and we have to be cautious.

A very important movement against geoengineering that talks a lot about the option of increasing albedo in deserts and the problems it could bring.

Conclusion, this solution is considered to be very expensive (trillion dollars per year, Shepherd et al, 2009), and dangerous, but very efficient.

That was all for today! see you soon!

:)