Marine Cloud Brightening

SRM: Marine Cloud Brightening

Marine Cloud Brightening (MCB) is the process wherein the concentration of cloud micro-droplets in marine cloud systems is increased to give them a whiter appearance, which ultimately increases the amount of solar radiation they reflect.

How? ….

To increase the concentration of micro droplets, cloud condensing nuclei particles would need to be increased. Proposed methods have suggested using sea salt - a naturally occurring and very abundant form of CCN.

Difficulties in the method arise over implementation. How could sea salt be injected into the troposphere and be evenly distributed? Aircrafts and ocean vessels have been put forward as possible solutions to this problem. Due to the short residence time of less than 10 days, 1500 ocean vessels with 28 billion nozzles distributing more than 50 cubic meters of sea-water droplets per second would  be required to counteract a doubling of atmospheric CO2.

Image 1: The first Flettner Rotor used instead of a sail on the Battner-Battner ship which crossed the Atlantic 

Image 2: A conceptual image of a Flettner Spray Vessel 

This calculation would seemingly lead one to eliminate MCB as a solution to fix climate change however the work of Salteret al., 2008 seeks to address this issue as it proposes the use of ‘Flettner Rotor Ships’ rather than ocean vessels or planes (see Image 1). These ships are wind powered, remote controlled, unmanned, can be moved seasonally and most importantly spray sea water droplets into the troposphere. The ships are thus a low carbon and much more inexpensive method than vessel ships or planes. Moreover as sea water is also inexpensive the method as a whole has a suggested cost of £2 billion (Salter et al., 2008). Depending on maintenance costs, this method could be very cost-effective in the long term, particularly in comparison to the much higher costs of SRM methods.

Image 3: A sea going yacht conversion by John Marples
that has incorporated Flettner Rotors

The feasibility of Flettner Rotor Ships proposal is limited as the technology needed to withdraw sea water and effectively seed the troposphere is incomplete and thus effective implementation is not yet possible. This is not to say the method would not work, but until the technology is available the overall feasibility of the ships is unknown. Further to this, MCB is limited as it can only counter warming from doubling of CO2 –any warming beyond this could not be countered by MCB. The method is therefore restricted as it is unable to return us to pre-industrial temperatures however it should not be ruled out entirely as it could be used to stabilize temperatures and keep them below critical thresholds.

In terms of its environmental impacts of MCB on the whole, various models (Latham et al., 2008; Jones et al., 2010; Rasch et al., 2009) have suggested that albedo enhancement will be enough to balance the radiative forcing for a doubling of CO2 and in some cases the temperature reductions have been asserted to also be enough to reduce polar ice loss (Parkes et al., 2012).  MCB also has the ability to target specific areas meaning those areas most at risk to warming can be addressed. Parkes et al., (2012) demonstrate this through their models which show cloud modification in the Northern Atlantic reducing summer ice retreats. Although the links between climate change and extreme weather are still being explored (for more info have a look at Joon's informative blog) it has been asserted that increased sea surface temperatures might be linked to hurricane intensification. MCB, due to its capacity to be applied regionally, could therefore be used in hurricane prone areas to counteract them occurring.

Geo-engineering wouldn’t be the same if it had no negative effects …. Thus as for the negative environmental effects of geo-engineering, firstly there are the localized changes in albedo. Although these local changes were just stated as an advantage they can also be a disadvantage – the weather systems and climate of the earth are non-linear and so predictions of the impacts upon regional climates and the global climate system itself are unfortunately shrouded with uncertainty and so a negative response to MCB cannot be entirely rule out. The non-linear nature of the planet also makes the link between MCB and polar ice reductions (Parkes et al.,2012) precarious as relations or more specifically responses are unlikely to be this in sync and predictable – particularly when current modeling and knowledge limitations about climatic responses and relationships are taken into account. Finally, MCB has been shown to cause changes to both the magnitude and pattern of precipitation. Having said that, a study by Jones and Haywood (2012) that uses the HadGEM2–ES model has shown that impacts on precipitation are less in degree to that simulated by previous studies which use much simpler treatments of this geo-engineering process. This finding is important as it highlights the need for more knowledge and research on the climate intricacies that are related to this methods implementation.

Marine Cloud Brightening, like all the geo-engineering techniques discussed thus far, has positives and negatives as a method. It is limited in that we do not know how applicable the method is due to a lack of knowledge about climate intricacies. Furthermore, if warming surpasses a doubling of CO2 the method cannot be used to bring us back to pre-industrial levels of warming and when current rates of warming are taken into consideration the method is unlikely to be able to fully rectify climate change. More research is thus needed to understand the effects of the method and after this it’s application can be determined. However, if the choice had to be made between sulfate aerosols and MCB, sulfate aerosols have been argued as being the better option (Jones et al., 2011). In my opinion therefore I think researchers should focus on developing sulfate aerosol methods rather than both.