Solar Geoengineering to Stop Annual Global Warming

Abstract

Solar geoengineering (SG) solutions have many advantages compared to the difficulty of carbon removal and reduction (CRR): it produces fast results; is shown here to have higher efficiency than CRR, is not related to fossil fuel legislation, and is something we all can participate in brightening the Earth with cool roofs, and roads. Methods detailed previously for SG requirements have been an issue primarily because of overwhelming goals and concerns about climate circulation. In this paper, higher feasibility is provided for solar geoengineering applications by focusing on estimates to stop annual increases in global warming rather than full mitigation. Annual SG area requirements are fifty times less compared to the challenge of full mitigation. This creates opportunities for future improvements both in SG and CRR. Unfortunately, SG to stop just a yearly increase in global warming is highly challenging as results show. We discuss partitioning SG land modification requirements per country area which reduces the worldwide task. We provide some ideas that should be helpful in Earth-brightening, stratosphere injection methods, reflective particle space clusters, and urban heat island modification.
To address yearly global warming, a multiple mitigation approach is suggested. As well, ‘negative solar geoengineering’ currently dominates worldwide practices with the use of black asphalt roads and roofs which discourages SG positive advances. Many issues need to be addressed for CRR and SG to be effective and these are discussed.

Full text

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
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Solar Geoengineering to Stop Annual Global Warming
Alec Feinberg
Northeastern University, DfRSoft Research,
Correspondence: dfrsoft@gmail.com
Highlights
 Solar geoengineering equations and estimates for annual global warming mitigation for Earth
brightening, stratosphere injection, desert surface treatment, Earth and space mirror-type
applications.
 Suggestions are provided for Earth brightening using AI drone technology, possible use of space
clusters, and solar geoengineering annual Earth brightening area requirements by country.
 Improved feasibility in solar geoengineering mitigation reducing costs.
 Estimates for annual solar geoengineering indicate a reversal requirement of -0.029Wm-2 per year
to mitigate an average global warming increase of 0.019oC/year.
 Annual solar geoengineering mitigating requirement estimates are approximately 50 times
reduced in reflective area requirements compared with prior full global warming mitigation
estimates.
Abstract: Solar geoengineering (SG) solutions have many advantages compared to the difficulty of
carbon removal and reduction (CRR): it produces fast results; is shown here to have much higher
efficiency than CRR, is not related to fossil fuel legislation, is something we all can participate in
brightening the Earth with cool roofs, and roads, and this assessment illustrates reasonable feasibility.
Methods detailed previously for SG requirements have been an issue primarily because of overwhelming
goals and concerns about climate circulation. In this paper, higher feasibility is provided for solar
geoengineering applications by focusing on estimates to stop annual increases in global warming rather
than full mitigation. Annual SG area requirements are fifty times less compared to the challenge of full
mitigation. This creates opportunities for future improvements both in SG and CRR. Although SG to stop
just a yearly increase in global warming is highly challenging as results show, this paper illustrates
feasibility in Earth-brightening, reflective particle space clusters, and urban heat island modification.
However, stratosphere injection methods appear excessively challenging. Results show that allocating
SG land modification requirements per country area to reduce the worldwide annual task is likely
feasible.
To address yearly global warming, a multiple mitigation approach is suggested. Unfortunately,
‘negative solar geoengineering’ currently dominates worldwide practices with the use of black asphalt
roads and roofs which discourages SG positive advances. Many issues need to be addressed for CRR and
SG to be effective and these are discussed. Results indicate that AI drone technology is likely key in Earth
brightening and may provide a key to meeting annual mitigation goals. Furthermore, higher space
shading feasibility is illustrated.
Keywords: Solar geoengineering Modeling, Space Mirrors, Earth Mirrors, Desert Modification, Space
Clusters, Stratosphere Injection

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
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List of abbreviations and nomenclature:
Solar geoengineering
SG
Reverse forcing change in Watts/m2
PRev
Zero global warming growth
ZGWG
Reverse forcing albedo change from a target
area T in Watts/m2
T
P
top of the atmosphere
TOA
Reverse forcing albedo change from a target
area T in Watts/m2
T
P
Solar radiation management
SRM
Re-radiation factor (62%)
f
Greenhouse gas
GHG
Secondary feedback amplification, taken as
2.15
AF
Long Wavelength
LW
Solar irradiance averaging 47%
Xc
Space irradiance: Space=4, else=1
XS
Transmissibility
TR
Annual reversal in Watts/m2
PASG
Target area
T
A
Target albedo, SG target’s albedo
modification
T

,
T


Earth area
E
A
TT


T


Temperature reversal
TR
Urban heat island (UHI) microclimate
amplification factor
HT
Average solar radiation 340Wm-2
4
o
S
Radiation change, at the TOA
TOA
R
Annual solar geoengineering
ASG
SO2 Injection rate, Particle Overlap
2
SO
I
, O
1. Introduction
This paper provides a method to obtain zero global warming growth (ZGWG) using annual solar
geoengineering (ASG). This will require timely annual construction rate reflective area solutions both on
Earth and possibly in space to reduce some of the sun’s energy to mitigate yearly global warming
increases. The objective is then to maintain the status quo allowing time for future improvements using
ASG. The IPCC worries about an increase of a 1.5oC rise over the pre-industrial period. This is estimated
to possibly occur around 2039-2043 at the current rate of yearly temperature increases. This can be
estimated from Figure 1 which shows this occurring around 2052. However, the graph displays changes
since 1975. The IPCC warning is referenced from the pre-industrial period. Translating Figure 1 to the
pre-industrial period requires adding about 0.17oC. Then this would occur around 2043 from the graph.
From the graph’s equation, the current rate of global warming is an increase in temperature of
0.019oC/year. To maintain the status quo for zero global warming growth, we can divide up the ASG
construction task into two parts for simplicity. Half relegated to stratosphere reflection (Table 1) or space
mirror-type methods (Table 2) and/or or solar dimming. Half relegated to land-based solutions such as
that proposed by project MEER [1] but on a larger scale (see Table 2). Therefore, our goal is to mitigate a
0.019oC/year global warming increase. This goal turns out to be about 50 times less mitigation in Earth
brightening area modification requirements compared to prior full mitigation estimates [2].
2. Method and Data
2.1. Zero global warming growth
In this paper, the approach is to provide estimates to achieve just enough solar geoengineering to
reverse the potential yearly increase in global warming. In this paper, this is referred to as annual solar
geoengineering. For example, global warming from 1975 to 2021 was 0.93oC. If a status quo annual solar

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
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geoengineering approach was applied, the ideal result would be a zero temperature increase. The
warming level would stay at 0.93oC. According to Fig. 1, the current temperature reversal for ZGWG is
TR=-0.01896oC/year (1)
Without ASG in 2022, the temperature increased to 0.949oC (≈0.93C+0.019oC).
Figure 1 Global warming linear trend assessment
3. Theory
The general requirements to offset a temperature increase in energy units is
TR=0.01896oC/year=0.102Wm-2/year (2)
This conversion to energy units can be obtained from the Stephan-Boltzmann relation where
4 4 2
2 1 2 2
( ) 0.102P P P T T Wm


     
(3)
where T1 is taken as the average surface temperature of the Earth of about 13.86oC and T2=13.86
oC+0.0189oC=13.9oC.
The SG strategy developed by the author [2] indicates to reverse all of the global warming that
occurred from 1950 to 2019 having a temperature rise of 0.95oC, would require a reversal of
2
Re 5.1
v
P Wm
  
. This is just the global warming rise from 1950 to 2019 of 0.95oC in energy units
where
 
4 4 2 4 4
Re 2021 1950
( ) 5.1 (287.95 ) (287 )
v
P T T Wm K K


        
. Here 287K=13.85oC is roughly
the average temperature of the Earth. Then we can write for full global warming mitigation (from 1950 to
2019) the reversal equates to [2]
2
Re 1
5.1 (1 )
v T F
P Wm P f A

     
(4)

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
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In this equation, the reverse forcing due to an albedo change of the target is denoted by
T
P
. We note that
increasing the reflectivity of a hotspot surface reduces its associated greenhouse gas effect This is estimated
in Eq. 4 with the 1+f term where f is approximately 0.62 [3]. This is due to the average re-radiation estimate of
62% [3].In this equation, we assume that feedback, which is dominated by water vapor, will also reverse.
That is, SG reverse forcing causes a cooling effect and cooler air holds less water vapor. Feinberg [3]
estimated a feedback value of AF=2.15 in 2019.
Then we can write

2
2
2.38 / 1.47 /
(1 )
T
Wm
P W m
f
  

(5)
This is the estimated goal for a total reversal of climate change from 1975 to 2021. However, in this paper,
we are only interested in zero global warming annual growth. Therefore, the ASG requirement for an
annual reversal is just (from Eq. 3-5)
2
22
2
1.47 / 0.102 / / 0.0293 / / .
5.11 /
ASG
Wm
P x W m Yr W m Yr
Wm
    
(6)
This is the main SG reverse forcing results for annual global warming mitigation.
It is helpful to note the SG advantage in Eq. 5. To mitigate the 5.1Wm-2 in Eq. 4 requires a SG
change of -1.47Wm-2 compared to trying to do it with GHG removal which would require the full
2.38Wm-2. This yields a work savings of 0.91Wm-2 (=2.38Wm-2-1.47Wm-2). This is a 38% (=0.91Wm-2
/2.38Wm-2) SG advantage [3] yielding much higher efficiency compared to CRR. That is in SG, we take
into account a 1+f re-radiation reduction in Eq. 5. In layman's terms, increasing the reflectivity of a
hotspot surface also reduces its associated greenhouse gas effect. As well, decreasing the reflectivity of a
hotspot surface also increases its greenhouse gas effect. These are fundamental principles in SG [3] and
indicate the importance of color choices in SG (see Sec. 5.2). This GHG-albedo effect is also a local factor
in UHIs due to high local CO2 presences [6] and UHI high water vapor feedback issues [6a].
3.1. Area estimates for annual solar geoengineering
To estimate the Eq. 6 area requirements for a -0.0293Wm-2 reversal to achieve zero global
warming growth, the approach is to use the author’s solar geoengineering estimate [2] provided by
 
()
4
So T
T ASG C T T T
E
XS A
P P X
A


      
(7)
In Earth brightening, as anticipated, we see the reversal is proportional to the target area AT, the amount
of irradiance Xc falling on the target with global averages of 47% [4], and the average solar energy over 24
hours is estimated as
4
o
S
, and in this case the space irradiance factor has XS=1. However, for space
mirror application, the optimal L1 point rotates around the Sun with the same angular speed as the Earth,
thus allowing an occulting disk to remain in a position where it casts continuous shade on the Earth.
Then in space mirrors estimates, the irradiance occurs 24 hours per day and shades a relatively small
Earth area that is not affected by its curvature. Normally, the ¼ factor occurs when half of the irradiance
is lost to the day-night cycle and half is lost to the earth’s curvature. To account for the increase in space
irradiance, XS=4 in Eq. 7.

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
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In addition, we can denote the change in the target’s albedo from
T

to its increase
T


. This
equation also provides provisions for targets in urban heat island (UHI) areas which can have
microclimate amplification effects denoted by HT [5, 6]. For example, in UHIs, the solar canyon effect
amplifies warming when buildings reflect light onto pavements amplifying heat at the surface. Other
issues include an increase in local CO2 GHG effect, local water vapor feedback, temperature inversions,
loss of wind and evapotranspiration cooling, increase in solar heating of impermeable surfaces from
building sides, and so forth [6].
4. Results
4.1. Cool pavement model estimate
As an example, consider the required area for worldwide cool pavements. Here we can consider
the average asphalt pavement albedo of about
0.1
T


, and using cool road methods, we can increase
the pavement albedo to
0.4
T


. Then considering an average irradiance of
0.47
C
X
and
1
S
X
,
and letting
1
T

, and using a 50% reversal annual climate mitigation goal for half of zero global
warming growth mitigation, the requirement is
   
2 2 1
_ 50% ( ) 340 0.47 0.3 0.01465
4
oS TT
ASG C T T T
EE
SX AA
P X W m W m Yr
AA

  

        
(8)
Solving we obtain the SG target area percentage for half of ZGWG of
0.0305%
T
E
Aper year
A
(9)
The pavement area that needs to be cooled for a change of
0.3
T


(Eq. 8) equates to
22
0.000305 196.6 6 60, 000
T
A x E mi mi
(10)
This yields a radius of 138 miles. This result is summarized in Table 2.
4.2. Space mirror shading estimates
We can translate any AT requirement alternately to a solar reflective space disc mirror type
application. In this case, we note that most authors consider the space-Earth L1 position as optimum.
Sánchez and McInnes [7] illustrate a shaded radius that is increased by an average factor of 5 on Earth
compared to that of the disc. Then, in this L1 position, the disc average radius reduction is 5 compared to
the corresponding Earth shadow radius requirements. In this case, the space disc needed at L1 will have a
required area reduction that goes as r2=25 compared to the shaded Earth area.
For the irradiance in space mirror estimation, we can take XC=100% and XS=4 (as discussed
above). Sun-shading can effectively translate to changing a target on Earth’s reflectivity to ~100% from
the average Earth’s albedo of 30%, so that
T


=0.7. Using these parameters and our 50% ASG goal, the
required disc radius is about 6.9 miles estimated using Eq.7. Results are summarized in Table 2.

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
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The reader may note, by comparison to the literature [7, 7a, 7b], the results here and the author’s
prior estimates [2] for the space disc area requirements, are orders of magnitude lower. For example,
Space discs as quoted in the literature {7, 7a] of the order of 700km to 1500km. These would shade
approximately 7.5% [7a] to 30% [7] of the Earth. This would cause very low dramatic temperatures
changes. Likely requirements for reasonable Earth shading mitigation are of the order of AT/AE=0.15% [2].
As well, annual requirements for 50% mitigation is 0.0015% (Table 2).
4.3 Annual Stratospheric Injection Estimates
Results appear quite challenging to meet Table 2 estimates for an annual SG effort for both Earth or
space mirror annual requirements. Unfortunately, there is no easy solution. Much has been written about
an alternate less expensive sun-dimming temporarily reflecting particle method such as calcium
carbonate placed in the stratosphere [8-13]. Alternately SO2 has been detailed. Here SO2 injected into the
stratosphere at the top of the atmosphere (TOA) reduces the sun’s energy reaching the Earth through
solar reflection reducing the solar radiation at the Earth’s surface. As an estimate for annual SRM, we can
use the equation estimated by Niemeier and Timmreck [14] where the reduction in radiation is
2
2 1 0.23
65 exp (2246 ( ) )
TOA SO
R Wm Mt S yr I

   
(11)
The actual injection rate
2
SO
I
(in units of MT(S)/year - megatonnes of SO2 per year) for full climate
reduction according to Eq. 6 requires 1.47Wm-2 (note this is often overestimated by other authors that
typically use about 5Wm-2. Such estimates do not take into account feedback and re-radiation reductions).
To provide the first-year reduction rather than full mitigation, the injection rate is 32x less as shown in
Table 1. Here full climate mitigation requires an injection of 6.9MT(S)Yr-1 for a 1.47Wm-2 reduction,
whereas, for the first year, the ASG goal is reduced to an injection of 0.216Mt(S)Yr-1 for a 0.01465 Wm-2
50% reduction. Unfortunately, depending on the SO2 dissipation per year, this would need to be doubled
in the second year, tripled in the third year, and so forth for ZGWG.
Table 1 SO2 Injection requirements for SRM
Stratosphere
Injection
Full
Reversal
Annual
50%
Reversal
RTOA (Wm-2)
1.47
0.01465
2
SO
I
(Mt(S)Yr-1)
6.9
0.216
Savings
0.4
32x
However, the area required in the stratosphere has not been fully established. Initial estimates by the
author found this estimate to be highly problematic [15]. Estimates are often equated to one Pinatubo
eruption which may be unreliable.
4.3.1 CaCO3 Stratospheric Injections – Alternate approach
In this section, a CaCO3 injection estimate is provided into the stratosphere for ZGWG. Here, we
can use the approach of Eq. 7 rather than Eq. 11. Consider the earth’s average albedo of about
0.3
T


,

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
7
then for this CaCO3 example, assume an increased reflectivity by a factor of 2 with a CaCO3 injection
bringing an area’s atmospheric albedo to
0.6
T


. Then, considering full irradiance,
1
C
X
, with
1
T

, and using a 50% reversal annual climate mitigation goal for half of zero global warming growth,
in Eq. 7 yields
   
22
_ 50% ( ) 340 (1)(1) 0.3 0.01465
4
oTT
SQSG C T T T
EE
SAA
P X W m W m
AA



        
(12)
Solving we obtain the SG target stratospheric area percentage first estimated due to the injection for half
of ZGWG yielding
0.0144% /
T
E
AO
A
(13)
We will likely have a fractional overlap of particles which is denoted as O. For example, for a 20% overlap
of particles, the increase in Eq. 13 would be
0.0144% / 0.8 0.018%
T
E
A
A
. Eq. 13 area equates to
22
28, 237 / 7.31 10 /
T
A mi O E m O
(14)
Estimates for the specific surface area (m2/g) of CaCO3 vary widely depending on the type of CaCO3 from
5-24 m2/g [16] to 30-60 m2/g [17]. If we conservatively use 10 m2/g, we can calculate the injection rate using
Eq. 14 as
22
7.31E10m /10m /g/yr./ =7310 metric tons/yr./ =0.0073Mt(CaCO3)/yr./O O O
(15)
For a 30% overlap, O=0.7 yielding
0.0073Mt(CaCO3)/yr./ =0.010Mt(CaCO3) O
(16)
This is only a partial solution as the particles will dissipate over time and require replenishing. The area
saturated is given by Eq. 13 and is
0.02%
TE
AA
. Then if this dissipates, in the following year the
requirement is
0.04%
TE
AA
. Because of this large area and its replenishing needs, in the annual
approach, particle injection is difficult because of the cumulative yearly requirements.
4.4 Overview of estimates
Table 2 provides an overview of the needed estimates to mitigate the annual global warming
growth trend of 0.019oC/day with SG. The goals in Table 2 are divided in half, with half relegated to Earth
brightening modification of the land surface and half to a space-type application. The objective for each is
to reduce the incoming solar energy by -0.01465Wm-2 per year. Note that in Table 2, the HT value, as an
example, is taken as 3 for UHI areas and conservatively 2 for Earth mirror use on urban rooftops as
implemented by project MEER [1] These vary depending on the UHI microclimate [6].
Table 2 ASG requirements for land and space
Land
Space

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
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Parameters
Pavements
Desert
Treatment
UHIs
Earth
Mirrors
Space Mirrors Parameters
Stratosphere
Injections
PASG(Wm-2)
-0.01465
-0.01465
-0.0147
-0.01465
PASG(Wm-2)
-0.01465
-0.01465
XC, XS
0.47, 1
0.92, 1
0.47, 1
0.7, 1
XC, XS
1, 4
1, 1
T



0.3
0.44
0.1
0.75
T



0.7
0.3
HT
1
1
3
2
HT
1
1
Land Requirements
Space Disc Requirements
CaCO3 Inj.
AT/AE
0.0305%
0.0106%
0.031%
0.0041%
AT/AE Earth Shade
0.00154%
0.0144%/O
AT (Mi2)
60,116
20,940
60,116
8061
Shade AT (Mi2, km2)
3023, 7842
~27,924,~74,322
Radius (Mi)
138
81.6
138
51
Shade Radius (Mi, km)
31, 50
~94.3, ~153.8
AT (km2)
1.56E+05
5.42E+04
1.6E+05
2.1E+04
Disc Area (Mi2, km2)
126, 327
-
Radius (km)
223
131
223
81.6
Disc Radius (Mi, km)
6.3, 10
-
Note the ASG requirement (Eq. 6) compared to full mitigation (Eq. 5) is ~50 times (=1.47Wm-2/0.029Wm-2)
reduced in energy flux requirements and area (per Eq. 7). For example, desert treatment is reduced from
the author’s initial estimate of 1.0% [2] to 0.010% for 50% annual mitigation in Table 2. Therefore the areas
in annual mitigation are a factor of 50 times smaller. Table 2 suggests several options including multiple
combinations that can be considered in annual mitigation.
4.5. Country solar geoengineering allocations
If we take Eq. 9 and double it for the task of a full year of climate mitigation it yields
0.061%
T
E
A
A
per
year. For land brightening, this equates to 0.21% of the Earth’s approximate land area. To aid solar
radiation management, we can allocate our goal amongst countries by their area. For example, consider
the requirements for the United States (with an area of 3.8E6 mi2) and England (with an area of 5E4 mi2).
Then the area requirements with surface albedo change
0.3
T


in Sec. 4.1 are:
 U.S. mitigation =0.00061 x 3.8E6mi2=2,318mi2/Yr or 6.4mi2/day with a radius of 27.2mi/Yr or
0.074mi/day
 England mitigation =0.00061 x 5E4mi2=30.5mi2/Yr or 0.084mi2/day with a radius of 3.1mi/Yr or
0.0085mi/day
Such goals are obtainable with drone spray technology (see Sec. 5.1).
If we have confidence in an UHI microclimate factor, HT=3 (see comment in Sec. 3.1), then according to
Eq. 7, in these UHI areas in the application of cool roads and roofs used to cool cities, results can be
reduced to
 US mitigation Goal=(0.00061 x 3.8E6mi2)/3=772.7mi2 with a radius of 15.7 miles
 England mitigation Goal=0.00061 x 5E4mi2=10.2mi2 with a radius of 1.8 miles
Such resurfacing of area tasks could be aided with the use of AI drone technology discussed in Sec. 3.4.
Although UHI areas are small, they are important due to their higher temperature issues.
Costs associated with solar geoengineering in space can similarly be divided possibly by a country's
population for a mitigation tax. This can aid in solar radiation space management.

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
9
4.6. Sun-Earth L1 point space particle clusters
Another similar idea that may merit investigation is to use a space particle cluster method instead of
space mirrors, but at or near the Sun-Earth L1 Point. A cluster of particles such as calcium carbonate or
SO2 in space may have a long suspension time. Diffusion would likely be slow due to low outer space
temperatures (~2.7K) and studies could be done to estimate issues. The main forces on a reflective particle
in a space cluster would likely be photonic and gravity forces between the sun and the Earth which
would need some balancing with proper positioning. The particles may eventually drift away and then
would need replenishing.
We can estimate the requirement for the solar reduction for an annual SG value using a method in the
author’s initial study [2]. For example, the incoming sunlight with the modification is
2 2 2
(1 .3) 476.32 0.0293 / 476.291
2
o
SW m W m W m

   
(17)
Solving yields So=1360.9163Wm-2. Then one finds 0.0837Wm-2 (=1361 Wm-2 -1360.9163Wm-2) is the
reduction required for the incoming sunlight.
If we measure the transmission of the incoming sunlight above and below the particle treatment,
the transmissibility (TR) from sun-dimming should be [2]
22
1360.9143 1361 99.994%TR W m W m


(18)
Measuring the transmissibility is likely a helpful method to assess the proper amount.
5. Discussion
5.1 Earth brightening using drones or mirrors
Solar geoengineering's state-of-the-art potential is a lot higher today. Drone technology has had
major advances in painting buildings [18] and agriculture spray methods [19]. For example, consider the
US goal for Earth brightening in Sec. 4.5 in terms of Earth brightening area per day
 U.S. Mitigation Goal Earth Brightening per day= 6.4mi2/day
A typical two gallons per acre agriculture drone can spray about 1 mi2/day [19a] which includes refills.
Then if we assume paint drones can be designed with similar capability, this requirement is about
 U.S. Mitigation Goal per day= 6 Drones/day
Although paint drones are not equivalent and rated this way compared to agriculture drones, technology
can likely provide similar capabilities for paint drones. Given AI technology and advances in drone
capabilities, we see that such goals likely can be met.
Possibly other technologies could be developed specifically for Earth brightening of buildings,
streets, desert areas, and UHI areas. New bright white surface treatments are being developed to help
cool the Earth [20]. Possibly an agency like SpaceX or NASA could vastly improve AI use in drones for
SG implementation. AI technology could allow for 24hrs a day drone SG work with automatic target
brightening, refilling, and target recognition. Furthermore, studies could help assess the best strategies to
try and improve coverage areas including mountain ranges since mountains cover about 24% of the
Earth. Brightening mountain areas could also increase condensation and snowfall as was done on the

A. Feinberg, Solar Geoengineering to Stop Annual Global Warming
10
Peruvian Andes mountain tops [21] which can increase snowfall and spring runoff to reservoirs in
drought-prone areas.
Annual mitigation using Earth mirrors, as suggested by project MEER [1], has several advantages.
Mirrors can be placed in areas of high irradiance, the albedo change is likely high, and when used in city
areas on roofs, HT>1. These all reduce the Earth’s annual SG requirements per Eq. 7.
5.2. Worldwide negative solar geoengineering
ZGWG is challenging enough. However, the problem of yearly increases in black asphalt roads,
rooftops, and even dark-colored cars worldwide makes the task harder. Although many issues like black
electric vehicles and gas cars do not contribute significantly to global warming, it encourages bad
behavior in solar color choices and does not contribute to the knowledge base.
In terms of climate change, these issues are a form of ‘negative solar geoengineering’. Currently,
it is estimated that roads occupy about 14% of all manmade impermeable surface areas [22] of which
impermeable surfaces occupy an estimated 0.26% of the Earth [23] Then the estimated area of the Earth
occupied by roads is 0.0364%. This is a bit higher compared to Eq. 9 estimated requirement for area
modification. By comparison to the estimated total impermeable surfaces, it is a factor of 8.5 times higher
than the Eq. 9 requirement (0.26%/0.0395%). This illustrates the difficult task of annual surface
modification area requirements. Feinberg [6] estimated that 1.1% of global warming is due to asphalt
roads which if brightened to concrete could have reduced global warming by 5.5%.
Negative solar geoengineering also has the potential to increase local and global water vapor
feedback as it creates increases in warm air which can hold more water vapor. This can increase feedback
that is dominated by water vapor.
6. Conclusion
In this paper, estimates are provided for annual solar geoengineering requirements. The result
illustrates several challenges. However, results provide more feasibility in SG with reductions in goals
that lead to a factor of 50 times reduction in area Earth brightening modification compared to full SG
global warming mitigation.
Many recommendations are made in this paper. These include the concept of ZGWG, drone
technology for SG, the suggested method of using space clusters that may be highly useful, and UHI use
of the HT value estimate of 3 in Table 2. Results in general point to challenging but feasible solutions.
Suggestions are provided for solar radiation management using country area allocations for Earth
brightening to improve feasibility (Sec 4.4).
It is pointed out that for SG to be effective; it is helpful to address many global warming
influences including the high yearly increases in energy consumption due to population growth and lack
of control [15]. Such issues are suggested to be included in Paris Agreement-type meetings. There is little
time left to meet the IPCC suggested 1.5oC goal as shown in Fig. 1. The longer we delay in implementing
a SG program, the more unacceptable our status quo will be due to increases in global warming reducing
our options. This paper provides improved solar geoengineering feasibility with annual mitigation goals
that are suggested can be allocated by country area which will supplement carbon removal and reduction
efforts to stay below the IPCC 1.5oC threshold.
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