Enhancing Urban Albedo to Fight Climate Change and Save Energy

Author:Elise Stull - Xiaopu Sun - Durwood Zaelke
Position:Former Law Fellow and now consultant at the Institute for Governance & Sustainable Development ('IGSD') - Visiting Law Fellow at IGSD focusing on fast-action mitigation strategies with both global and Asia perspectives and has participated in a successful pilot project to reduce Perfluorocarbon ('PFC') emissions from aluminum refining in China ...
Increasing worldwide surface albedo, or reflectivity, starting
in urban areas, can help fight climate c hange by offsetting
radiative forcing1 from carbon dio xide (“CO2”) and other
climate forcing gases and aerosols. This can delay impacts of
dangerous anthropogenic interferenc e with the climate system
and complement strategies to make long-term reductions in CO2
emissions. Installation of high-albedo “cool roofs” across urban
areas c ould also redu ce future CO2 emissions from fossil fuel
derived electricity used for air conditioning. Several U.S. states
have policies supporting cool roof installation to reduce energy
usage, i mprove air quali ty, and allevia te the urban heat island
effect. The U.S. Department of Energy has announced a series of
initiatives to improve and broaden implementation of cool roof
technologies. Such policies are supported by a number of scien-
tific studies that demonstrate the benefits of albedo enhancement
both to cities and to the global climate.
The goal of climate change policy is to avoid “dangerous
anthropogenic interference with the climate system,” according to
the United Nations Framework Convention on Climate Change
(“UNFCCC”).2 As Parties to the UNFCCC continue negotiating
the elements of a fair and effective treaty, emissions of green-
house gases an d aerosols continue to incre ase. The observed
global temperature, which is estimated to have risen about 0.76°C
since pre-industrial times, also increases. Temperature thresh -
olds for tipping points, such as the collapse of the Greenland Ice
Sheet and the dieback of the Amazon Rainforest, could be passed
with an increase of 1-4ºC over pre-industrial levels. According
to one study, the “committed” level of warming from emissions
through 2005 is 2.4°C (1.4–4.3°C). This 2.4°C is comprised of
the observed warming plus an additional 1.6°C that is temporarily
lagged in the oceans and masked by cooling sulfate aerosols that
are now being reduced for public health reasons.3 This 2.4°C and
associated climate change impacts put the climate system within
the zone of “dangerous anthropogenic interference” already.4
International climate policy has focused primarily on long-
term reductions of CO2, the principle greenhou se gas res pon-
sible for 50% of radiative forcing since 1750.5 Howe ver, due
to t he profoundly long atmosp heric life of CO2—centuries to
millennia6—and the expec ted contribution fro m c ommitted
warming, “climate change that takes plac e due to increases in
carbon d ioxide concentrations is largely irreversible for 1,000
years after emi ssions stop.”7 To delay warming while pursuing
aggressive CO2 mitigation, climate policy must include mitiga-
tion of the 50 % of radi ative forcing from non-CO2 gases and
aerosols, as we ll as carbon nega tive strategi es to draw down
excess CO2 already in the atmosphere, starting with bio-seques-
tration through biochar.8 The main non-CO2 forcers are black
carbon, hydrofluorocarbons, methane, and tropospheric (ground
level) o zone. These ga ses and aerosol s have atmosph eric life-
times of days to a decade and a half, so reducing them can pro-
duce a fast response in the climate system. Like these other fast
action strategies, increasing worldwide urban albedos could help
delay warming and associated impacts.
Albedo refers to the percentage of solar radiation reflected
by a surface or an object measured on a scale from zero to one,
with one being the most reflective.9 Surfaces with high albedos,
such as snow-covered land, reflect high percentages of shortwave
solar radiation preventing conversion to longwave infrared radia-
tion that heats both the surface and the atmosphere. Surfaces with
low albedos include the ocean and land with vegetative cover, so
deforestation and land use changes since pre-industrial times have
increased albedo and actually produced a negative radiative forc-
ing of −0.2W m−2, with uncertainty of ± 0.2W m−2.10 This albedo
enhancement is providing a small offset, compared to the 1.6 W
m−2 forcing from CO2
11 and the comparable forcing from non-
CO2 warming agents. Recent studies demonstrate that enhancing
urban albedo can produce additional negative radiative forcing
without the downside of environmental damage.12
A recent stud y by researchers at the Lawrence Berkeley
Nationa l L aboratory (“LBNL” ) co ncludes that increa ses in
by Elise Stull, Xiaopu Sun, and Durwood Zaelke*
* Elise Stull is a former Law Fellow and now co nsultant at the Instit ute for
Governance & Sustainable Development (“IGSD”). Her research concentrates
on climate tipping points, in particular those that w ould impact islan ds, such
as sea level rise and ocean acidification, and on fast-action climate mitigation
strategies. She has supported island States at multiple United Nations climate
Xiaopu Sun is a Visit ing Law Fellow at IGSD f ocusing on fast-a ction mitiga-
tion strategies with both global and Asia perspectives and has participated in a
successful pilot project to reduce Perfluorocarbon (“PFC”) emissions from alu-
minum refining in China. She holds an LL.M. from Harvard, and an LL.B. and
an LL.M. with a concentration in Environmental Law from Peking University.
Durwood Zaelke is President and founder of IGSD, Director of the International
Network for Environmental Compliance & Enforcement, Co-Director and co-
founder of the Program on Governan ce for Sustainable Development at the
Bren School of Environmental Science & Management, University of California,
Santa Barbara, and founder of the International & Comparative Environmental
Law Program at American University Washington College of Law.
6FALL 2010
urban surface albedos in temperate and tropical regio ns by 0.1
could produce a one-time offset f or emitted CO2 of approxi-
mately 57 gigatons (“Gt”) CO2.13 For comparison, it is estimated
that ener gy-related CO2 emis sions were ~28.8 Gt in 20 07 and
total greenhouse gas emissions were ~42.4 Gt CO2-equivalent in
2005.14 The LBNL researchers use a detailed land surface model
developed by NASA to perform simulations of boreal summers
(June to August) over a twelve-year period. Based on simula-
tion-generated data, they calculate that the potential offsets from
increasing roof albedos by 0.25 and pavement albedos by 0.15
would be ~31 Gt CO2 from roofs and ~26 Gt CO2 from pave-
ments for a total of 57 Gt CO2.15
The LBNL study is a follow up to a paper published in 2009
by the same research team using many of the same variables,16
the results of which were questioned by a review that concluded
offset potential had been overestimated.17 However, at least part
of th e criticism of the 2009 paper—center ing on the estimate
of the percentage of gl obal land area occu pied by urban sur-
faces18—was addressed by the 2010 study, which uses satellite
data rather than global estimates.19
Simply removin g radi ation from the c limate system by
increasing surface albedo does not, of course, fix the underlying
problem of accumulating emissions of CO2 and other climat e
warming gases and aerosols.20 However, cool roofs, made from
light-col ored, hig hly refle ctive mat erials, indirectly decrease
CO2 emissi ons by keeping buildings cool, reducing electricity
needs for air conditioning.21 Cooler buildi ngs and pavements
can also reduce summertime temperatures, improve air quality,
and help to alleviate o ther problems associat ed with the urban
heat island effect.22 On average, increased r ooftop albedo was
found to decrease building cooling costs more than 20% for a
rooftop albedo increase of 40-50%, according to the 2009 LBNL
study.23 The LBNL study als o found that in the United St ates,
combined energy and air qu ality sav ings fro m urban albedo
enhancement could exceed $2 billion per year.24
An independent study of rooftop albedo enhancement based
on models finds that average daily maximum urban temperature
decreased by 0.6ºC and daily minimum temperature decreased
by 0.3ºC, suggesting increasing albedo is an effective method of
diminishing urban heat island effect.25 Although the authors cau-
tion that energy savings from reduced air conditioning should be
weighed against increased heating costs in winter where appli-
cable, they also note that as air conditioning becomes more com-
mon globally, the role of cool roofs may expand.26
On July 19, 2010, U.S. Secretar y of Energy Stev en Chu
announced that initiat ives to insta ll cool roofs and promote
albedo enhancement are underway at the Department of Energy
(“DOE”).27 The DOE plans to construct cool roofs where cost
effective on its own properti es and is advising other fede ral
agencies to undertake similar projects.28 To help facilitate such
projects, the DOE published the m anual Guidelines for Selec t-
ing Cool Roofs, which contains technical information for both
agencies and commercial builders.29
In 2005, California introduced cool roofs as an option for satis-
fying the state’s strict efficiency requirements, and, in January 2010,
cool roofs became mandatory for certain structures.30 Other states
and cities have enacted similar regulations, including requiring cool
roofs under some circumstances.31 The federal government now
intends to play a leading role, installing cool roofs on DOE buildings
across the country, including its headquarters in Washington, DC.32
The offset potential of surface albedo enhancement has
inspired proposals for more expansive imp lementation through
geoengineeri ng, which is d efined as efforts to counte ract the
greenhouse effect by directly managing Earth’s energy budget.33
Geoengineering typically entails large-scale manipulation of the
environment; therefore, urban albedo enhanc ement and other
strategies that effect relatively small changes in radiative forcing
are sometime s referred to as “soft geoengineer ing” or “geoen-
gineering light.”34 One type of albe do modification-based geo-
engineering scheme entails covering arid regions or low albedo
deserts with heat refl ecting sheets,35 while another focuses on
switching to natural or bioengineered grasses, shrubs, and crops
that are lighter in color and more reflective.36
Unlike installations of cool roofs and pavements, these geoen-
gineering schemes do not provide benefits of energy efficiency or
urban heat island alleviation. Moreover, large-scale surface albedo
enhancement may cause negative effects including extreme regional
cooling and interference with local weather.37 However, these
effects can be monitored as desert albedo enhancement is scaled up,
and the albedo can be returned to its original level if impacts are too
severe, unlike the potential impacts of other types of geoengineering
schemes, for example, putting mirrors into orbit in space.
Enhancing urban albedo is an easy and effective way to
reduce electricity needs and diminish urban heat island effect,
and it can be implemented quickly, as existing roads and roofs
are replace d and new ones constructed. Several states and the
U.S. government have policies including incentives to encourage
installation of cool roofs for efficiency purposes. Increasing albe-
dos of urban roofs and pavements globally would also produce cli-
mate mitigation in the form of an offset to radiative forcing from
CO2. Together with other non-CO2 fast-action mitigation strate-
gies, urban albedo enhancement can help delay peak warming and
associated impacts while aggressive cuts are being made to long-
term CO2 emissions. Increasing urban albedo is the “light” coun-
terpart to large-scale surface albedo modification, which, among
geoengineering options, is preferred to other schemes that carry
significant risk of unforeseen and unmanageable side effects.
Endnotes: Enhancing Urban Albedo to Fight Climate Change
and Save Energy on page 60