Effects of Urban Surfaces and White Roofs on Global and Regional Climate
ABSTRACT
Land use, vegetation, albedo, and soil-type data are combined in a global model that accounts for roofs and
roads at near their actual resolution to quantify the effects of urban surface and white roofs on climate. In
2005, ;0.128% of the earth’s surface contained urban land cover, half of which was vegetated. Urban land
cover was modeled over 20 years to increase gross global warming (warming before cooling due to aerosols
and albedo change are accounted for) by 0.06–0.11 K and population-weighted warming by 0.16–0.31 K, based
on two simulations under different conditions. As such, the urban heat island (UHI) effect may contribute to
2%–4% of gross global warming, although the uncertainty range is likely larger than the model range pre-
sented, and more verification is needed. This may be the first estimate of the UHI effect derived from a global
model while considering both UHI local heating and large-scale feedbacks. Previous data estimates of the
global UHI, which considered the effect of urban areas but did not treat feedbacks or isolate temperature
change due to urban surfaces from other causes of urban temperature change, imply a smaller UHI effect but
of similar order. White roofs change surface albedo and affect energy demand. A worldwide conversion to
white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures
by ;0.02 K but to warm the earth overall by ;0.07 K. White roof local cooling may also affect energy use, thus
emissions, a factor not accounted for here. As such, conclusions here regarding white roofs apply only to the
assumptions made.