SRM 101

Solar Radiation Management (SRM). Perhaps the more controversial of the two strands of geoengineering. If you conduct a Google search then results are dominated with articles outlining the risks and impracticalities. Let's look at the fundamentals:

What?

The aim of SRM is to reduce the amount of solar intensity reaching earth's surface by reflecting it back to space. Six key methods are summarised as follows:

(From Caldeira et al., 2013, adapted from the Royal Society, 2009)

Where?

The methods range from being implemented on earth's surface (plant reflectivity, whitening of the ocean), to the earth's atmosphere (stratospheric aerosols, whitening of clouds), even as far as low earth orbit (space-based schemes).

How?

Widespread implementation of SRM methods would need international cooperation and agreement because of their impacts of a global nature. For example, numerical models have found that any local or regional implementation of methods would likely have global impacts (Caldeira and Wood, 2008). This raises questions regarding the governance of SRM, as all nations must ratify its implementation. A totalitarian approach, rather than a democratic one, lends itself better to global scale application (Stilgoe, 2015) but ethics will likely always stand in the way of this becoming reality.

Why?

With uncertainty surrounding the climate's tipping point, and the decadal to centennial timescales it would take for CDR methods to come into effect, SRM is seen as the only option for immediate action for some. Whilst it doesn't have the capacity to reduce greenhouse gas concentrations in the atmosphere, it is able to reduce the effects of them. For those who believe that it is too late, SRM as seen as the only feasible option left.

Why not?

As above, a reduction in solar radiation will not solve the root of the problem - the increase of greenhouse gas concentration in the atmosphere. Despite the reflection of sunlight away from earth, it will likely not be possible to restore all climatic fields, temperature and precipitation, for example (Caldeira et al., 2013). There is also great uncertainty in the impacts of these methods. Models cannot possibly predict the true extent of global impacts, let alone regional ones (see the 'environmental risk' ratings in the Royal Society's table above). Reduced warming from SRM methods would reduce the global mean of precipitation (Bala et al., 2008; Caldeira and Wood, 2008; Lunt et al., 2008), shifting the hydrological cycle and likely increasing drought frequency in many regions.

To top it off, failure of these methods would mean catastrophic impacts. Earth would experience a significant, short-term climate forcing that would mean warming at rates that ecological systems could not cope with and further mass carbon dioxide release (Matthews and Caldeira, 2007), leaving earth systems worse off than present.

I don't know what to think. Never underestimate the capacity of internal systems (i.e. CDR) to moderate carbon flux between sources and sinks, but this is a slow process that just cannot keep up with the demands of a two-degree warming limit agreed at COP21 in Paris. A human civilisation built on reactionary principles means that we create unfeasible reactionary targets, and these targets demand the implementation of reactionary solutions... enter SRM. I don't want to it to be the solution, but I fear that compulsive human nature has dug us a hole that leaves us no other choice.

Agree or disagree:

Two-degree warming limit is an unfeasible benchmark?

Two-degree warming limit is meaningless?

SRM is the only feasible solution left?

High risk, high reward, or not?

Am I a pessimist?