Any winning contenders?

This blog has considered a wide variety of Geoengineering options....so what is the verdict? Are any of them a viable option for solving climate change?

Let us firstly look purely at the potential of each option: To compare Geoengineering options, the potential of each proposal to cool the climate is quantified in terms of radiative forcing (RF). RF describes any imbalance in the Earth’s radiation budget that could be caused by human intervention or natural processes. Once a RF is applied, then the Earth’s radiation budget will usually adjust itself and this will be seen through changes in global temperatures. IPCC (2007) states that the present anthropogenic RF is equal to 1.6 Wmˉ². This is the target that many Geoengineering proposals have adopted to counteract. Are any successful? However, what if mitigation continues to be unsuccessful? Lenton and Vaughan (2009) postulate that without mitigation, anthropogenic C02 forcing could reach approximately 7 Wmˉ² by the end of the century. And even with strong mitigation, anthropogenic RF may still exceed 3 Wmˉ². Therefore, which Geoengineering option/options could counteract this?

Placing sun-shades in space ad increasing planetary albedo through the injection of aerosols into the stratosphere are the only two options with the potential to counteract >3 Wmˉ². Moreover, these options could even be scaled up to counteract further anthropogenic RF. The RF potential of enhancing cloud albedo could also achieve 3 Wmˉ² globally, but the effects would be regional and patchy. This is also true for injecting aerosols, depending on when the aerosols are injected. These shortwave measures appear to have the most potential to roughly cancel the anthropogenic C02 RF, as long as strong mitigation measures are also implemented. The remaining measures such as enhancement of the albedo of deserts, urban areas, crops, grasslands etc, could be used in combination and could achieve a partial cancellation of the anthropogenic C02 RF.

Long-wave measures that influence the carbon cycle through the capture of CO2, either by plants, biochar or chemical means, could be used in conjunction to achieve a RF of approximately 2.5 Wmˉ². These options appear to be much more effective compared to ocean fertilisation, where tests have shown that this option only has a RF of 0.23 Wmˉ² (Lenton and Vaughan, 2009).

Figure 1:

So from looking purely from a Geoengineering potential perspective, air capture and storage, the use of sun-shades and stratospheric aerosols, appear to be the options that would induce the greatest radiative forcing...this can be seen in Figure 1. However, what about the risks....While the use of sun-shades and injections of aerosols may have the most potential, they are also the most risky. If deployment is suddenly stopped then rapid warming could occur (Wigley, 2006) (see post: ‘Geoengineering Projects – are they viable of just plain crazy!’). However, carbon cycle engineering carries less risk associated with failure. Therefore, in my opinion, air capture and storage along with afforestation and the use of biochar appears to be the best option. Compared to the remaining Geoengineering proposals, these options are the least risky, and when used in combination could be equally successful as the short-wave options. Moreover, they have the support from the IPCC and afforestion and bio char could also provide other benefits to society not just carbon sequestration. However, their effectiveness is over a long time scale. Furthermore, these options could only counteract 3 Wmˉ² of the anthropogenic C02 RF, what happens if society fails to mitigate emissions? What about the remaining 4 Wmˉ²? This is why many academics are emphasising the need to investigate the option of stratospheric aerosols (Lawrence, 2006; Schneider, 1996; Lenton and Vaughan, 2009; Victor, et al., 2009; Govindasamy and Caldeira, 2000; Matthews and Caldeira, 2007). Even though this option does have a significant risk element, it may be society’s last resort if rapid climate change occurs. The question is, is there any harm in having an insurance policy? Does it mean we will go out and take more risks if we do?