Geoengineering the Goldilocks monsoon

A tangent, albeit an interesting one...

Geoengineering - possible saviour for the Earth or one-way street to disaster induced by mankind's arrogance? It is a matter of opinion either way, but for the first time geoengineering was acknowledged in the IPCC AR5 Summary For Policymakers as a possible course of action. More recently an article dubbed Transforming Earth appeared in the New Scientist, noting that the location and planetary geoengineering methods that will have to take place, can now be identified (Figure 1 - click to enlarge). This got me thinking...how might geoengineering affect the South Asian monsoon? 

Figure 1 - Various proposed geoengineering projects and 
their locations around the globe (New Scientist)

Geoengineering is generally split into two camps (Desmogblog) - solar radiation management and carbon dioxide removal. The Enhanced Weathering centred in India in Figure 1 is an example of CO₂ removal. It's based on the idea of crushing minerals such as Olivine into a powder and applying it to the land surface, creating a larger surface area for chemical weathering to occur and thus increasing the draw-down of CO₂. Potential impacts are changing the river/surface water alkalinity and this could have an impact upon one of the foundations of South Asia - agriculture. Dependent upon the materials used, enhanced weathering could lead to better water efficiency of crops and more productive soils (Hartmann et al., 2013 - great study if you are interested in the detail).

Possibly more well known is stratospheric aerosol injection to manage solar irradiance and 'dim' the Earth by reflecting more shortwave radiation back into space (Figure 2). This is one of three possibilities, alongside albedo enhancement of marine stratocumulus clouds and sunshades in space, that Lenton and Vaughan (2009) have identified as having the potential to bring the climate closer to pre-industrial levels. You might remember from an earlier post that the major monsoon driver is the moisture flux from ocean to land driven by temperature gradients - any change in the amount of solar radiation reaching the surface could impact upon this. Tilmes et al. (2013) modelled the effects of stratospheric aerosol injection and noted that global average precipitation decreased by 4.5%. The impacts also appeared much more pronounced during months of heavy monsoonal rains, leading to precipitation reductions of 7% in North America, 6% in East Asia and South America, 5% in South Africa and 2% in India. 

Figure 2 - Stratospheric Aerosol Injection to cool the Earth by enhanced
reflection of shortwave radiation back to space (Carnegie Institution)

Bala et al.. (2008) looked into the impact of geoengineering on the water cycle and they cite a study demonstrating the effects of the Mt Pinatubo eruption in 1991. Although short-term, the sulphate released into the stratosphere led to a substantial reduction in precipitation and run-off decreased to a record low, something that would hugely impact South Asia agriculture accounts for 21% of India's GDP (World Bank). Robock (2012) notes that any small scale tests of stratospheric aerosols would be hard to detect from interannual variability and so a full-scale implementation would be needed to fully investigate the impacts, which sounds rather risky to me!   

Like many geoengineering 'solutions', the effects of any efforts, even regional, are likely to have global effects - especially with stratospheric aerosol injections. It is largely down to the nations with wealth to implement geoengineering, but a history of colonialism may make parts of the world distrustful of the admirability of the wealthier nations intentions. Furthermore, once started the impacts of stopping could be worse in the long run as this blog shows. Worryingly, a recent news article notes that geoengineering trials that do not involve material input into the oceans, whilst widely believed to be illegal, are perfectly legal according to the language of environmental treaties. This begs the question of when and how mankind goes about geoengineering - if done in the wrong manner, the consequences upon a sensitive system such as the South Asian monsoon could be huge. 

Next up...precipitation