Review and Critical Analysis of International UHI Studies

� 10.5 MtCO2 emissions per year from the in‐direct energy reduction for all UHI
countermeasures, assuming that the US scales to global in proportion to its share of
energy consumption and the in‐direct effect is about 25% of the direct effect in energy
reduction impacts, as quoted in an LBNL study.
Therefore, the total energy reduction mitigation effect potential is about 53 MtCO2 per year and is
slightly greater than a 1000 th of the only global estimate for the negative radiative potential effect.
It is important to note however, that 44Gt could be approximately 50% lower were a different
approach used to compare the equivalency of the radiative forcing reduction to a tonne of CO2.
It is clear that both principle methods examined by the literature demonstrate that the urban heat
island countermeasures have significant potential to mitigate global warming impacts. The
simple estimates established above are derived from claims made in the literature indicating that
the negative radiative forcing effect has a much greater mitigation potential than the
direct/indirect effect methods. It is important to recognize that although both methods
demonstrate significant mitigating potential there is a particular need for further research efforts
to verify the magnitude of the negative radiative forcing mitigation potential as there are far
fewer assessments of this phenomenon and yet the studies which have been conducted suggest a
very considerable mitigation potential. Furthermore, greater emphasis needs to be placed on
exploring the sizable benefits that can be achieved through the mass implementation of the high
albedo surfaces that induce the negative radiative forcing effect.
5.3 Policy Review
There has been significant work in the cool roof arena, particularly in the US by the Lawrence
Berkeley National Laboratory (LBNL) based in California. They have been at the forefront of
research, modeling work and testing of materials and their work has been the catalyst to many
pilot programs and policies in the US. Green roofs & urban green areas and cool pavements
however, have received less attention and as a result knowledge, testing and quantified benefits
are less well known and thus far fewer examples of policy exist solely for these measures.
In general terms current policy is hard to keep track of. Frameworks for policy exist at a Federal
level but building codes, standards and programs are run at a State and Local Government level.
The programs developed at Federal level simply act as a framework or reference point for State
and Municipalities. In Germany 14,000 Municipalities exist each with different building laws and
related policies.
It was clear from the papers that a comprehensive policy review for all measures across the globe
has not been undertaken, LBNL have undertaken one for the USA and specific studies of
activities in the UK, Germany and Tokyo have also been undertaken.
Significant barriers are faced in implementing policy which explains why some mitigation
measures are more advanced than others, these include a lack of research, modeling and general
understanding concerning the benefits of the countermeasures, policy development time scales,
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