There are no natural clouds in the pictures above. The
white-wisps [thin lines] are produced by chemtrails
Solar geoengineering is commonly seen to be subject to what some
call its ‘incredible economics’ (Barrett
2008) and, more specifically, its ‘free driver’ effect: its direct
costs are so cheap compared to its potential
climate impacts so as to reverse many of the properties of the
so-called ‘free rider’ problem governing carbon
mitigation decisions and climate policy more broadly (Wagner and
Weitzman 2012, 2015, Weitzman 2015).
The governance problem becomes one of cooperation to restrain rather
than increase action. Here we probe these economic assertions and
review the capabilities and costs of various lofting methods
intended to deploy sulfates into the lower stratosphere, the leading
proposed method of solar geoengineering (Keith 2000, Crutzen 2006,
National Research Council 2015).
Stratospheric Aerosol Injection (SAI) would require lofting hundreds
of thousands to millions of tons of material each year to altitudes
up to ∼20 km. Here we seek answers to three questions: if SAI
deployment were to commence within the foreseeable future with the
tools and technologies at our disposal, how would such deployment be
physically achieved, how much would it cost, and could it be done in
National Academies of Sciences (NAS), Engineering and Medicine
(1992) provides an early review of SAI deployment options, deriving
detailed pricing for naval rifles and two different balloon systems
(appendix Q.11). McClellan et al (2012) attempt to provide the first
comprehensive answer to this question, publishing results from an
earlier Aurora Flight
Science Corporation analysis (McClellan et al 2010).
Like McClellan et al (2010, 2012), and later reviewed by Moriyama et
al (2017), we explore an array of different SAI lofting technologies
and given our more specific mission criteria, we conclude that
aircraft are the only reasonable option. Unlike them, we conclude
that modified existing business jets are incapable of flying above
∼16 km, a conclusion confirmed directly by the manufacturers of the
jets in question.
This directly contradicts both McClellan et al (2010, 2012)and IPCC
(2018). The latter demonstrates the large influence McClellan et
al’s analysis has had on the broader conversation. IPCC (2018)
states that ‘there is high agreement that aircrafts after some
modifications could inject millions of tons of SO2 in the lower
stratosphere (∼20 km)’ (chapter 4).
IPCC cites three studies in support of that statement, including
McClellan et al (2012). However, both of the other two studies, in
turn, base their conclusions, in large part, on McClellan et al’s
earlier analysis. Irvine et al (2016)
also cites the other (Davidson et al 2012), which, in turn, cites
McClellan et al (2010). Robock et al (2009) provides one further
independent analysis, reviewing capabilities of military fighters
We agree with Robock et al (2009) that military fighters are capable
of reaching ∼20 km, but they are incapable of
sustained flight at that altitude (see table 2 below).
We further conclude that no other existing aircraft have the
combination of altitude and payload capabilities required for the
mission, leading us instead to the design of a new plane.
We propose such a plane and call it SAI Lofter (SAIL), describing
its basic specifications and providing detailed cost estimates for
its design, manufacture, and operation under a hypothesized solar
geoengineering scenario of halving the increase in radiative forcing
from a date 15 years hence. We do not seek to foretell future
technological breakthroughs, nor do we guess at costs in 50 or 100
years when next-generation deployment technologies would likely
Further, we do not consider solar geoengineering methodologies other
than SAI or materials other than sulfate aerosols (Keith 2000, Keith
et al 2016). We instead hope to illuminate discussions of direct SAI
deployment costs based on existing technologies, thereby
facilitating further benefit-cost comparisons and grounding ‘free
driver’ discussions in concrete
numbers supported by science-based SAI deployment scenarios and
sound aerospace engineering.
2. Stratospheric aerosol deployment scenario
Following a research hypothesis proposed by Keith and Irvine (2016),
we consider a limited SAI deployment scenario (Sugiyama et al 2018)
intended to cut in half the rate of temperature change from the
first year of the program onward.
While such a scenario is less ambitious (and less environmentally
risky) than those aimed at keeping temperatures constant from a
certain date forward, it is more ambitious than SAI merely holding
the rate of temperature change constant (MacMartin et al 2014).
We further assume anthropogenically driven radiative forcing of
∼2.70 W m−2 by 2030, with an assumed decadal increase of ∼0.5 W m−2
that is roughly consistent with the Representative Concentration
Pathway (RCP) 6.0 scenario (Moss et al
2010, IPCC 2013). Assuming the desire to cut this rate of increase
in half implies the need for SAI to reduce
radiative forcing by ∼0.25 W m−2 by the end of the first decade of
deployment. The implied change in global average surface
temperatures from SAI deployment is −0.2 K per decade, with an
assumed global average temperature sensitivity of 0.8 K per W m−2
We focus on SAI using sulfates, not because they are optimal—they
may not be (Keith et al 2016)—but because the long record of prior
analyses on both efficacy and risks of sulfate deployment (National
Research Council 2015) renders them the best understood and
therefore least uncertain material with which to commence in this
hypothetical scenario of partial deployment.
In the base case, we assume a topof-atmosphere (TOA) sulfate forcing
sensitivity of −0.25 W m−2 per Tg S yr−1 , a value toward the lower
end of recent estimates. Pierce et al (2010) estimates −0.34 W m−2
and Dai et al (2018) derives a range from below −0.50 to over −2Wm−2
for injections between 30 °N and 30 °S. Other estimates for
different injection scenarios, roughly converted to TOA values,
range from −0.15 W m−2 (Kuebbeler et al 2012) to −0.33 W m−2 (Niemeier
and Timmreck 2015), while Pitariet al (2014) shows results from the
Geoengineering Model Intercomparison Project (GeoMIP), here roughly
converted to TOA, for one point of injection at the equator ranging
from −0.47 to −0.98 W m−2.
Table 1 summarizes the base-case SAI deployment scenario for the
first 15 years of a program commencing in 15 years. The year 2033 is
It is not the most likely start date, nor are we suggesting it is an
optimal one, but any deployment much sooner seems highly unlikely
based on scientific and political
Hypothesized base-case SAI scenario in the first 15 years of
deployment commencing in 15 years. Tons of S carried are half of
tons SO2 dispersed.
b 2033 2.850 2.825 0.2 −0.02
2034 2.900 2.850 0.4 −0.04
2035 2.950 2.875 0.6 −0.06
2036 3.000 2.900 0.8 −0.08
2037 3.050 2.925 1.0 −0.10
2038 3.100 2.950 1.2 −0.12
2039 3.150 2.975 1.4 −0.14
2040 3.200 3.000 1.6 −0.16
2041 3.250 3.025 1.8 −0.18
2042 3.300 3.050 2.0 −0.20
2043 3.350 3.075 2.2 −0.22
2044 3.400 3.100 2.4 −0.24
2045 3.450 3.125 2.6 −0.26
2046 3.500 3.150 2.8 −0.28
2047 3.550 3.175 3.0 −0.30
a Assumes −0.25 W m−2 per Tg S.
b Assumes 0.8 K per W m−2 average temperature sensitivity (see
The Dept. of Solar Radiation Management
Is attempting to block the sun’s heat a good idea—or a reflection on
our pathetic efforts to cut carbon emissions?
January 25, 2015 Brian Palmer
Solar Radiation Management (n.): a set of geo-engineering strategies
intended to minimize global warming by reflecting the sun’s energy
away from the earth.
Solar radiation management sounds like corporate-speak. (VP for
Solar Radiation Management, anyone?) In fact, it’s one of the most
controversial concepts in climate change mitigation.
The idea is fairly straightforward. First, some Climate Change 101:
About 30 percent of the energy arriving from the sun is reflected
back out into space, mostly by clouds and ice. The planet—its seas,
lands, creatures, buildings, etc.—absorbs the remaining 70 percent,
and gases such as carbon dioxide and methane trap some of that heat
within the atmosphere. So here’s the pitch for SRM: What if we could
bounce more of the sun’s energy back into space in the first place,
preventing it from ever getting trapped by the greenhouse effect?
How might we make that happen? One wildly impractical proposal is a
network of space mirrors. The problem with this idea isn’t just that
it sounds like something a fourth-grader would dream up—it would
take a tremendous amount of energy to launch those mirrors into
space. (Wasting energy by burning more fossil fuels is precisely
what we’re trying to avoid.) Another option is to mist seawater into
the air. Those white clouds would reflect solar energy before it
reaches the darker, energy-absorbing ocean. This strategy has
moderate support among SRM advocates.
To understand the most popular approach, though, think back to the
1991 eruption of Mount Pinatubo in the Philippines, if you can
remember it. (I envy your youth if you can’t.) The volcano spewed a
huge amount of sulfur dioxide, a precursor of sulfuric acid. Within
a year, the sulfuric acid layer stretched around the entire planet.
Tiny droplets of sulfuric acid reflected sunlight back into space
before it reached earth, and the planet’s temperature dropped by
approximately 1 degree Fahrenheit for more than two years.
SRM advocates say we could do something similar—and without killing
hundreds of people and displacing thousands more, as Pinatubo’s
eruption did. We could fly high-altitude planes or float balloons
capable of spraying sulfur dioxide into the atmosphere. (Other
chemicals, such as titanium dioxide, are also under consideration.)
To offset a doubling of atmospheric CO2, which represents a global
temperature increase of between 1.5 and 4.5 degrees Celsius,
researchers think we would have to inject around five megatons of
sulfur dioxide annually into the atmosphere.
Five megatons sounds like a lot—and it is—but SRM enthusiasts point
out that coal-fired power plants already emit nearly 55 megatons of
sulfur. This is just a 10 percent increase on that number, and for a
Are you sold? Not so fast. There are many, many complications, and
even the most open-minded conservationists are skeptical of SRM. For
one thing, it’s largely unproven. Just because a volcano can do
something doesn’t mean we can do it—especially in a controlled
fashion. In addition, the effects of SRM are likely to vary by
region. The process could make some areas colder than they currently
are, depressing agricultural production. Russian farmers, for
example, might have something to say about this. SRM might also
diminish our motivation to reduce carbon emissions. That’s
an issue because excess carbon causes many problems beyond higher
temperatures. The oceans would continue to acidify, for example,
killing off species like clams, oysters, and corals, and disrupting
For now, think of solar radiation management as the panic room of
climate change mitigation. Few people really want to go there, but
it’s still tempting to some, especially since our current rate of
progress on carbon reduction suggests things could get pretty bad.
Let's hope we can turn things around before it comes to that.
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