Solar Radiation Management - Surface

Solar Radiation Management (SRM)

The main aim of SRM methods is to drastically, if not entirely, reduce net radiative forcing. They way in which the methods propose to do this is through making the Earth more reflective in order to balance the positive forcing of greenhouse gases with the negative forcing of the absorption of solar radiation (Royal Geographical Society, 2009). Achieving this balance would produce a reduction in global mean temperatures which in turn, could lessen the impacts and risks of global warming (Lane and Bickel, 2013).

Discussions about SRM have been going on since the 1960s however it was a largely ignored area of climate science, a topic considered taboo due to concerns that public discussions of SRM would lessen the incentives for political action (Kiehl, 2006).

Attitudes towards SRM only recently changed in response to the editorial essay of Paul Crutzen (2006) which urged a more systematic consideration of SRM. Crutzen’s (2006) paper gave ground to SRM research and debates within the wider climate change debate.

Two trends within the SRM debates are evident. The first is the fact that climate change has lost political salience due to failed GHG control efforts while the second is that it has become hard to deny the lack of control over GHG emissions.

The place of SRM has risen and subsequent debates over its proper governance are growing. Recent debates have been marked by hearings in UK Parliament and US Congress, various expert panels and national research programs have been created and there has been the formal resolution by the Convention on Biological Diversity (Mercer et al, 2011). Having said that, dispite the evolving dialog there range of experts who participate in debates is narrow (Lane and Bickel, 2013) and little is to be known about the public’s awareness and feelings towards geo-engineering due to  lack of data (Mercer et al., 2011).

Impact of different SRM methods on Solar Radiation Fluxes

There are three broad categories, or more specifically, heights at which SRM methods can operate (see above). Firstly, solar radiation can be reflected at the surface, it can be reflected in the air and lastly space based techniques can be used to reduce solar radiation. In the following posts I will look at each these SRM areas.

First up … surface albedo approaches of SRM…

Surface based approaches of SRM aim to reflect solar radiation by making the surface brighter. Surface albedo, therefore, is a measure of the reflectivity, or brightness, of the earths surface.

There are a number of methods that have been proposed such as white roof methods and the brightening of human settlements, more reflective crop varieties and grasslands, desert reflectors, reforestation and ocean albedo (Royal Geographical Society, 2009). Methods could that could be developed in the future include plant morphology modifications to increase albedo such as altering leaf characteristics to increase leaf pubescence, surface waxes, or canopy architecture to maximize albedo.

The overlying issue with surface approaches of SRM is that relative to their cost they are inefficient. The implementation costs of these methods range from billions (roof whitening) to trillions (desert reflectors) while albedo adjustments are minute.

From reading about SRM an important factor brought to attention in the effectiveness of SRM methods is height. The closer to earth an SRM method is, the less efficient it is at increasing surface albedo and ultimately reducing global temperatures.

Further to this, looking at the energy balance of the climate, the planets surface albedo is currently about 0.15 but to cool the planet 0.17 would be needed (Royal Geographical Society 2009). A 0.02 increase might seem rather modest however when you factor in the proportion of the Earth’s surface that is covered by oceans – which have a very low albedo – the figure does not seem quite so modest as we are only left with land to make up that increase and within that cohort there are further restrictions of what land can be used as not all land surface is available for brightening.

Conclusion:

The literature surrounding surface SRM methods is not expansive but perhaps this is due to a lack of support, particularly in comparison to other more popular SRM methods such as stratospheric aerosol injections that seemingly offer more promise (Lane and Bickel, 2013). Nonetheless one can conclude that the discounting the common argument of environmental impacts that is put forward by those opposed to geo-engineering, SRM methods simply do not provide the global cooling that would be desired based upon their costs. As they do not reduce GHG the level of cooling they cause is key and as it as of yet cannot be achieved it seems it is just being left behind.

Thanks for reading.