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I saw the catchy Phys.org news title Artificially cooling planet 'risky strategy,' new research shows and then looked at the open access article, in Nature Communications (14-Nov-2017 online) Impacts of hemispheric solar geoengineering on tropical cyclone frequency, Jones et al. doi:10.1038/s41467-017-01606-0

Abstract:

Solar geoengineering refers to a range of proposed methods for counteracting global warming by artificially reducing sunlight at Earth’s surface. The most widely known solar geoengineering proposal is stratospheric aerosol injection (SAI), which has impacts analogous to those from volcanic eruptions. Observations following major volcanic eruptions indicate that aerosol enhancements confined to a single hemisphere effectively modulate North Atlantic tropical cyclone (TC) activity in the following years. Here we investigate the effects of both single-hemisphere and global SAI scenarios on North Atlantic TC activity using the HadGEM2-ES general circulation model and various TC identification methods. We show that a robust result from all of the methods is that SAI applied to the southern hemisphere would enhance TC frequency relative to a global SAI application, and vice versa for SAI in the northern hemisphere. Our results reemphasise concerns regarding regional geoengineering and should motivate policymakers to regulate large-scale unilateral geoengineering deployments. (emphasis added)

The paper seems to warn against single-hemisphere solar geoengineering. Was that the plan to begin with, and nobody until now thought that cooling one hemisphere but not the other one might be problematic?

Or is this paper simply stating something more common-sense, for example "if you do it wrong, it won't work right".

Was there in fact any plan for unilateral geoengineering deployments before this was published, or is there a bit of grandstanding along with the science?

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I think the introduction of the paper itself covers this adequately:

… a growing number of studies have investigated regional SG application scenarios, which could prove preferential to a global application by restricting the geospatial magnitude of the climate response or by being used to target specific climate changes8,9,10,11.

The cited references are:

  1. Robock, A., Oman, L. & Stenchikov, G. L. Regional climate responses to geoengineering with Tropical and Arctic SO2 injections. J. Geophys. Res. 113, D16101 (2008).

  2. MacCracken, M. C. On the possible use of geoengineering to moderate specific climate change impacts. Environ. Res. Lett. 4, 045107, https://doi.org/10.1088/1748-9326/4/4/045107 (2009).

  3. MacMartin, D. G., Keith, D. W., Kravitz, B. & Caldeira, K. Management of trade-offs in geoengineering through optimal choice of non-uniform radiative forcing. Nat. Clim. Change 3, 365–368 (2013).

  4. Haywood, J. M., Jones, A., Bellouin, N. & Stephenson, D. Asymmetric forcing from stratospheric aerosol impacts Sahelian rainfall. Nat. Clim. Change 3, 660–665 (2013).

Of those, [9] seems the most obviously relevant, although it covers more techniques than just SAI. One particularly relevant passage from [9] reads:

… materials lofted this high and staying in the atmosphere for extended periods tend to spread out to cover the globe. As a result, both their climatic influences and any unintended side effects (e.g., increased scattering of incoming solar radiation that diminishes the efficiency of direct-beam solar energy technologies) tend to be global in extent.

Since [9] is focused on discussing regionally-targeted geoengineering techniques, the presumed global spread of SAI is here being mentioned mainly as a potential disadvantage.

I think Jones et al. are actually raising two concerns with their work:

  1. Unilaterally deployed SIA targeted at a particular region could have negative side-effects. This is the topic most relevant to your question. As the references show, there were indeed plans for this, at least in the sense that it had been discussed in the literature for some years. I don't know of any state drawing up concrete plans for SIA stations yet, but it's probably a good idea to raise these concerns before the policy train gets rolling.

  2. SIA might be deployed at a single site as a globally targeted SG technique, with the assumption (as seen in [9]) that it doesn't matter where you do it because the aerosols will spread evenly over the globe in any case. Jones et al. show that this will not necessarily happen.

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  • $\begingroup$ Thanks for the thorough answer! I remember several decades ago many Americans thought about moving to Australia or New Zealand to avoid nuclear fallout, believing that mixing was very slow. I'd thought this was common knowledge. OK I'll take some time to track down these papers and have a look. $\endgroup$ – uhoh Nov 15 '17 at 9:55

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