It’s often repeated uncritically that aerosol geoengineering will “do nothing” to prevent ocean acidification, but the reality is more complex.
We know from past volcanic eruptions that the diffuse light created by stratospheric aerosol injections can potentially promote productivity in the terrestrial biosphere, although there is significant regional heterogeneity (Gu et al., 2003; Mann et al., 2012). This is the first indication that there is more going on than just a simplified, decoupled ocean and atmosphere response. Clearly we need to look at the interaction of the carbon cycle between all reservoirs, including the terrestrial sink.
When we do this using relatively simple (Earth system) models, we find that indeed the response from the terrestrial biosphere is very important in looking at the effects of aerosol geoengineering on ocean acidification (Matthews et al., 2009). What we see is that the lower temperature and increased carbon uptake by the terrestrial biosphere actually slows pH decrease a little relative to a non-geoengineering scenario (but has no change on aragonite saturation levels). Other experiments suggest that this increase in terrestrial carbon uptake might occur due to decreased higher latitude heterotrophic respiration and increased tropical productivity (Tjiputra and Otterå, 2011). These experiments indicate that while the cooler ocean waters are more soluble to atmospheric CO2, this is largely offset by a reduction in the ocean-atmosphere CO2 partial pressure gradient. It should be noted that these OA reductions are small relative to an unchecked emissions-driven scenario.
Thus, aerosol geoengineering may actually slightly reduce the rate of ocean acidificaiton due to increased terrestrial carbon uptake, but more study is needed. Even with geoengineering, however, ocean acidification is a serious threat to ocean life.
- Gu, L., D. D. Baldocchi, S. C. Wofsy, J. W. Munger, J. J. Michalsky, S. P. Urbanski, and T. A. Boden (2003), Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis, Science, 299(5615), 2035–2038, doi:10.1126/science.1078366.
- Mann, M. E., J. D. Fuentes, and S. Rutherford (2012), Underestimation of volcanic cooling in tree-ring-based reconstructions of hemispheric temperatures, Nature Geoscience, 5(3), 202–205, doi:10.1038/ngeo1394.
- Matthews, H. D., L. Cao, and K. Caldeira (2009), Sensitivity of ocean acidification to geoengineered climate stabilization, Geophys. Res. Lett., 36, 5 PP., doi:200910.1029/2009GL037488.
- Tjiputra, J. F., and O. H. Otterå (2011), Role of volcanic forcing on future global carbon cycle, Earth System Dynamics, 2(1), 53–67, doi:10.5194/esd-2-53-2011.