wrote:
On Mar 26, 5:39 pm, "Bob F" wrote:
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.- Hide quoted
text -

- Show quoted text -

Then explain why when the experiment was actually done in FL,
using white shingles vs black, it only made a few percentage
points difference in AC energy usage for occupied homes.
And then factor in that the percentage of the earth's surface
that is covered by roofs is negligible compared to the total
surface.

You are talking about A/C power consumption. The article was talking about heat
released to the atmosphere or reflected through it to space.

The "experiment" looked only at the energy consumed by the A/C in the house, not
the heat released to the atmosphere above the house. Insulation alone could
account for why the A/C was not that affected, but would have no effect on the
atmospheric temp rise.