Imagine
a world where the rooftops and pavements of every urban area are
resurfaced to increase the reflection of the Sun’s light rays. Well,
this is exactly what a group of Canadian researchers have done in an
attempt to measure the potential effects against global warming.

   

In a study published today, 13 April, in IOP Publishing’s journal Environmental Research Letters,
researchers from Concordia University created this scenario to see what
effect a global increase in surface reflectance would have on global
temperature and our own carbon dioxide (CO₂) emissions.

   

They
estimate that increasing the reflectance—commonly known as albedo—of
every urban area by 0.1 will give a CO2 offset between 130 and 150
billion ton. This is equivalent to taking every car in the world off the
road for 50 years, assuming a single car gives off around 4 tonnes of
carbon dioxide a year.

   

This
could also provide huge financial gains: CO₂ is currently traded at $25
a ton meaning savings could be in the range of $3300 and $3800 billion
dollars. Albedo is measured on a scale ranging from 0 for a
non-reflecting, perfectly black surface to 1 for a perfectly white
surface. The albedo of all roofs can be increased, on average, by 0.25
and all paved surfaces can be increased by about 0.15. The researchers
believe this will increase a city’s overall albedo by about 0.10.

   

Researchers
have long proposed that changing the albedo of a surface could be an
effective way of reducing CO₂ emissions. A change could effectively cool
buildings that would usually retain heat and therefore reduce the use
of air-conditioning systems; it could also improve outdoor air quality
and offset the warming that the world is currently experiencing.

   

In
this new study, the researchers showed that increasing the albedo of a
1-m2 surface by 0.01 would have the same effect on global temperature,
over the next 80 years, as decreasing emissions by around 7 kg of CO₂.

   

The
researchers used a dataset of all global urban areas, called the Global
Rural and Urban Mapping Project (GRUMP), to give a realistic estimate
of the effects of a global albedo change. In addition to the very large
carbon dioxide offset, the researchers calculated a potential decrease
in temperature of about 0.07 C.

   

Completely
changing the surfaces of all the world’s roofs and pavements seems like
a mammoth task; however, the researchers believe that it is possible if
promoted in the right ways.

   

“Typically
roofs are resurfaced (or changed) about every 20-30 years; paved
surfaces are resurfaced about every ten years. When roofs or paved
surfaces are installed, they can be changed to materials with high solar
reflectance, typically at no incremental cost,” the researchers write.

   

Lead
author Professor Hashem Akbari said: “It is all based on planning,
codes and policies. If we really put the nuts and bolts in place, we can
get close to 100 per cent of urban areas increasing the albedo of
surfaces.”

   

Fast facts:

• Over 50% of the world’s population currently lives in urban areas. This is expected to increase to 70% by 2040.
• Pavements and roofs comprise over 60% of urban surfaces (25% roof and 35% pavement).
• According to the GRUMP model, the combined size of global urban areas is around 2 million km2.

The long-term effect of increasing the albedo of urban areas

Source: Institute of Physics