Dear All,
Last summer Warren Washington invited me to write an article in /The
Bridge/, the quarterly magazine of the National Academy of Engineering.
It has just been published and the entire issue of the journal is
available online at
https://www.nae.edu/228883/Spring-Bridge-Issue-on-Engineering-and-Climate-Change
. The issue is about engineering and climate change, and you can read
the Editor's Note starting on p. 5 on "Engineering and Geoengineering
Approaches to Climate Change."
You can download the pdf of my article at
http://climate.envsci.rutgers.edu/pdf/RobockBridge.pdf
Robock, Alan, 2020: Benefits and risks of stratospheric solar radiation
management for climate intervention (geoengineering). /The Bridge/,
*50*, 59-67.
Table 2 is my most recent list of potential benefits, risks, and
concerns of implementing stratospheric climate intervention. And I want
to remind you that this list is not meant to be evaluated by counting
the number of items on each side of the list. Potential benefit 1 is
that it could reduce global warming and many of its negative impacts.
The question for future policy makers is whether this potential benefit
outweighs the many potential risks.
This reminds me to make a couple comments about Pete Irvine and David
Keith's latest article on using SRM to cut global warming in half, thus
reducing the impacts on precipitation,
https://iopscience.iop.org/article/10.1088/1748-9326/ab76de . I have
seen several articles touting it as a good idea, since it would provide
some benefits with fewer negative impacts on soil moisture and
precipitation. But:
1. This is not a new idea. I pointed this out in a message to this
list a year ago, on March 12, 2019, but they still fail to reference
previous work:
Jones et al. (2013), of which Peter Irvine, the first author of this new
paper, is a co-author, showed in Figs. 1 and 2 for the BNU model, that
if you only compensate for half the warming, you get no change in
precipitation. So the result in this new paper is to be expected and
not surprising at all.
Kravitz et al. (2015), of which Peter Irvine, the first author of this
new paper, is also a co-author, lays out the GeoMIP experiments that are
now being completed as part of CMIP6. The G6 experiments are exactly
the scenario studied in this new paper, using half the forcing of
RCP8.5. I don’t understand why it was ignored by Irvine and Keith (2020).
Tilmes et al. (2016) used the NCAR climate model to simulate
stratospheric geoengineering to partially reduce global warming, and
found decreases in temperature and precipitation extremes, and also
examined aridity changes.
MacMartin et al. (2019) showed that for moderate deployment scenarios,
changes in regional temperature and precipitation patterns as compared
to business as usual would not be detectable over much of the planet
even by the end of this century, which is the same thing as found in
this paper.
2. I think it is important to remind ourselves that temperature and
precipitation are not the only potential climate impacts from SRM. Even
if we could be happier with how those change as compared to no
mitigation at all, there are so many other things that need to be
considered before implementation. As Irvine and Keith point out,
governance is likely the greatest challenge. But, in addition there are
ozone depletion, acid rain, ecosystem impacts, agricultural impacts,
aesthetics, ethics, and unknowns (see details in my Table 2). I am sure
they agree with me that much more research needs to be done on these and
other topics before society can consider implementation.
In one sense I agree with their assertion that “The level of
radiative forcing is among the most important choices that society will
have to make about solar geoengineering.” The question is whether it
will ever be greater than zero. If we come to that conclusion sooner
rather than later, this will erase the false hope that solar
geoengineering will solve the global warming problem and perhaps
increase the needed push to leave the fossil fuels in the ground.
*References*
Jones, Andy, Jim M. Haywood, Kari Alterskjær, Olivier Boucher, Jason N.
S. Cole, Charles L. Curry, Peter J. Irvine, Duoying Ji, Ben Kravitz, Jón
Egill Kristjánsson, John C. Moore, Ulrike Niemeier, Alan Robock, Hauke
Schmidt, Balwinder Singh, Simone Tilmes, Shingo Watanabe, and Jin-Ho
Yoon, 2013: The impact of abrupt suspension of solar radiation
management (termination effect) in experiment G2 of the Geoengineering
Model Intercomparison Project (GeoMIP). /J. Geophys. Res. Atmos./,
*118*, 9743-9752, doi:10.1002/jgrd.50762.
Kravitz, Ben, Alan Robock, Simone Tilmes, Olivier Boucher, Jason M.
English, Peter J. Irvine, Andy Jones, Mark G. Lawrence, Michael
MacCracken, Helene Muri, John C. Moore, Ulrike Niemeier, Steven J.
Phipps, Jana Sillmann, Trude Storelvmo, Hailong Wang, and Shingo
Watanabe, 2015: The Geoengineering Model Intercomparison Project Phase 6
(GeoMIP6): Simulation design and preliminary results. /Geosci. Model
Dev./, *8*, 3379–3392, doi:10.5194/gmd-8-3379-2015
MacMartin, D. G., Wang, W., Kravitz, B., Tilmes, S., Richter, J. H., &
Mills, M. J. (2019). Timescale for detecting the climate response to
stratospheric aerosol geoengineering. /Journal of Geophysical Research:
Atmospheres/, *124*, 1233–1247. doi:10.1029/2018JD028906.
Tilmes, S., B. M. Sanderson, and B. C. O'Neill (2016), Climate impacts
of geoengineering in a delayed mitigation scenario, /Geophys. Res.
Lett./, *43*, 8222–8229, doi:10.1002/2016GL070122.
--
Alan
Alan Robock, Distinguished Professor
Associate Editor, Reviews of Geophysics
Department of Environmental Sciences Phone: +1-848-932-5751
Rutgers University E-mail: rob...@envsci.rutgers.edu
14 College Farm Road http://people.envsci.rutgers.edu/robock
New Brunswick, NJ 08901-8551 USA ☮ http://twitter.com/AlanRobock
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