Carbon Dioxide Removal over Solar Geo-Engineering

At this point, I feel it necessary to explain why this blog has heavily focused on the forms of Geo-Engineering that involve Carbon Dioxide Removal (CDR) rather than Solar Geo-Engineering techniques.

The first is that CDR methods address the problem at the root of climate change, the carbon produced through anthropogenic emissions rather than attempting to deal with the issue in a roundabout way by reducing the amount of solar radiation reaching Earth. This ties in neatly with the second reason, there are likely to be fewer unintended consequences associated with CDR techniques. By reducing the atmospheric levels of carbon, CDR methods are attempting to reverse the current trend to prior levels that have already been experienced and studied rather than shifting our climate in an unknown way. Unexpected shifts could lead to further problems that could be worse thanthe current situation.

Another justification for CDR methods is that there are other indirect benefits. Removing carbon dioxide from the atmosphere can help to reverse the current trend of ocean acidification due to the ocean-atmosphere flux, benefiting marine species such as coral which are under the threat of extinction.

Carbon Dioxide Removal approaches are also easier to control than Solar-Engineering methods. It is relatively easy to stop capturing atmospheric CO₂ or stop ocean fertilisation compared to removing large sun reflectors from space or removing chemicals pumped into the upper atmosphere. In addition, pumping aerosols into the upper atmosphere could lead to ozone depletion.

Furthermore, there is likely to be less human error involved in CDR practices in comparison to Solar Geo-Engineering methods because atmospheric carbon dioxide has been widely studied whereas the implications of altering the amount and distribution of solar energy reaching Earth is understood to a lesser degree and because of this makes Solar Geo-Engineering techniques far more risky despite possibly bringing about faster climate responses. Solar Geo-Engineering is seen as having greater issues surround governance, equity and ethics that also create other disincentives for implementing some of these concepts.

Figure 1: Solar Geo-Engineering: (a) reflectors (b) stratospheric aerosols (c) cloud brightening
(d) increasing ocean reflectivity (e) reflective plants (f) roof whitening