wrote:
On Mar 26, 4:03 pm, Metspitzer wrote:
The idea of painting roads and rooftops white in order to combat
carbon emissions has been around for years. It is surprisingly simple
and effective and yet has not been implemented much.

A study at the Lawrence Berkeley National Laboratory found that
cooler pavement and roofs leads to cooler cities and an overall
cooler world.

Since buildings with white roofs reflect far more sun than those with
black roofs, these buildings stay cooler. Less air conditioning has
to be used, lowering the overall energy required to run the building.

Also buildings with black roofs heat the space below them and this
heat is carried spread by the wind. This raises the ambient air
temperature in what is known as the urban heat island effect. Black
roofs also radiate energy back into the atmosphere to be absorbed by
clouds. This heat is then trapped by the greenhouse effect.

As such, white roofs is one of the quickest and most cost-effective
ways to reduce our carbon emissions. In an initiative launched by the
Energy Department, the federal government hopes to exemplify the
benefits by using these light roofs on their buildings.

http://newscenter.lbl.gov/news-relea...-roofs-offset-...



I say it's total BS. The best study I saw on roof color was
done in FL. They took a bunch of identical houses, put varying types
and color of roofs on them, fully instrumented
the houses, and measured during AC season.

The conclusion was that if you had a shingle roof, it made
about a 10% difference in energy usage if you had a black
rood or a white roof. And that was the energy usage with
the houses unoccupied. They did another test when they
were occupied and the energy usage difference dropped to
just a few percent. Which makes sense, because when
occupied the energy usage is going to be higher, because
people are opening door, turning on TVs, cooking, etc.

It would also seem to me that it's junk science to suggest
that lighter roofs lead to a cooler world. X amount of solar
radiation is hitting the earth. Almost all of it is going to go
into heating it.
So, it's hard to believe that because something is white
that radiation is going back from earth to outer space.

Nevertheless, it happens. That's one of the issues with global warming. As the
glaciers and polar ice caps melt off, the land/sea under them will absorb heat
currently radiated back into space by the white ice/snow, warming the planet
even more. Roofs could make a similar difference, and that difference would not
be fully expained by air conditioning costs.

Imagine covering roofs with mirrors. Do you think they would radiate energy into
space? If you don't, would you expect someone in space would see the glare if
the reflection were aimed at them? What they see is energy reflected into space.
White paint reflects almost as much energy as a mirror, but not directionally
like a mirror, so less of the reflection might make it to space than a mirror's
reflection.

White paint for the roads - not the slippery kind they use for road markings.
That would be stupid and cause accidents.