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White Roofing as Silver Bullet to slay Global Warming?

by a siegel Mon Sep 15th, 2008 at 11:18:57 PM EST

Reflective roofing has long seemed one of the best geoengineering options to help turn the rising tides of Global Warming. An opportunity to reduce energy use through reduced cooling demand and longer lasting roofs, to improve urban life (and cut energy requirements) by reducing urban heat island impacts, and to contribute to fighting global warming by reflecting solar radiation back into space.

It seems, however, that this opportunity might be even greater than previously believed. Global Cooling: Increasing World-wide Urban Albedos to Offset CO2 (pdf) suggests that white roofing of just 100 cities could handle Global Warming temperature increases.

This study comes from some of the nation's top experts in roofing, from Heat Island Group at Lawrence Berkeley National Laboratory which focuses on this serious urban challenge:

"Heat Island research is conducted to find, analyze, and implement solutions to the summer warming trends occurring in urban areas, the so-called 'heat island' effect. We currently concentrate on the study and development of more reflective surfaces for roadways and buildings."

According to Global Cooling,
a 1,000-square-foot roof -- the average size on an American home -- offsets 10 metric tons of planet-heating carbon dioxide emissions in the atmosphere if dark-colored shingles or coatings are replaced with white material.

Globally, roofs account for 25% of the surface of most cities, and pavement accounts for about 35%. If all were switched to reflective material in 100 major urban areas, it would offset 44 metric gigatons of greenhouse gases, which have been trapping heat in the atmosphere and altering the climate on a potentially dangerous scale.

That is more than all the countries on Earth emit in a single year. And, with global climate negotiators focused on limiting a rapid increase in emissions, installing cool roofs and pavements would offset more than 10 years of emissions growth, even without slashing industrial pollution.

This is quite impressive and a path that almost certainly is worth pursuing ... even aggressive. To be clear, simply addressing temperature will not deal with all of the challenges related to CO2 emissions. For example, reflective roofing would do nothing relative to the acidification of the oceans and this threat to ocean (and human) life. But, the temperature impact in terms of cooling could be quite important in helping to create breathing space as humanity lowers its carbon footprint through reduced energy use combined with ever-more low/no-carbon energy sources.

The core geoengineering principle should be:

win-win-win. A proposal that, in a systems of systems effort, provides multiple wins and does not solely address temperature. Thus, a proposal that offers real potential for improving economy, reducing carbon, and contributing to reduced temperature (both directly, somehow, and indirectly through reduced carbon loads or carbon capture) would seem to merit greater prioritization than high-cost efforts that would solely impact "temperature" but not impact (or worsen) the carbon load equation.

And, this is the case with reflective roofing on a large scale,
"I call it win-win-win," Akbari said. "First, a cooler environment not only saves energy but improves comfort. Second, cooling a city by a few degrees dramatically reduces smog. And the third win is offsetting global warming."

Hat tip to Grist , EcoGeek, and Treehugger. LLBL press release.

on this one, as I have a reflective ("aluminized" paint) roof. And I have to say that, when I recoat about every 5 years, I feel a slight difference in heat accumulation in the house during the hottest days of Summer.

But - albedo means that the reflected light (and not necessarily infrared radiation by the way) is taking a second trip through the atmosphere. If the atmosphere is full of 'greenhouse gases', then there is another gauntlet of heat-sinks to run for the reflected radiations.

One reason that albedo seems important for the ice-caps at the poles may be due to the fact that insolation per unit of surface area is low due to the angle of that surface wrt to the incoming radiation. So - is albedo significant, or is it simply the lower heat input per surface area unit?

Also, what are the relative concentrations of 'greenhouse gases' at the poles vs. areas nearer the equator? If higher or nearly equal at the poles, then the gauntlet is actually increased, due to the longer path through the atmosphere at polar angles to the Sun.

In any case - as you agree, I'm sure - reduction of energy use and reduction of fossil-fuel-based-energy- production are more important. Meantime, though, I'm due for a re-coating, so thanks for the reminder.

paul spencer

by paul spencer (spencerinthegorge AT yahoo DOT com) on Tue Sep 16th, 2008 at 01:03:31 AM EST
and don't worry about that second trip through the atmosphere under high CO2 conditions.  At worst it will be caught and converted to heat, which, if you don't reflect it off your roof, is what will happen anyway.  

The Fates are kind.
by Gaianne on Tue Sep 16th, 2008 at 04:06:14 AM EST
[ Parent ]
Also, what are the relative concentrations of 'greenhouse gases' at the poles vs. areas nearer the equator?

CO2 and CH4 are well-mixed in the atmosphere, so the variations between different latitudes are minimal after the first year or so.

Water vapour is much more variable, but it is also much more transient - H20 cycles out of the atmosphere in weeks at the most.


-- #include witty_sig.h

by silburnl on Tue Sep 16th, 2008 at 06:10:30 AM EST
[ Parent ]
Thanks, Luke.

gaianne - I didn't say that it wasn't significant. I'm wondering just how significant, though - meaning data, not merely energy input calculations.

One of my brothers-in-law told me recently that he had read that forests decrease albedo, and, therefore, increase global warming. For obvious reasons I think that this is not true in any meaningful sense. One of the counterarguments that comes to mind - just at the theoretical level - is that light (primarily red wavelengths) is actually being 'used' to promote a reaction - photosynthesis - not converted to heat. In addition some heat (infrared radiation) accelerates that reaction. My b-i-l could not provide source, but my assumption (yes, I know how the verb form breaks down) is that someone just looked at insolation and stopped right there, perhaps comparing albedo of fir canopy to albedo of wheat stubble - or of concrete. (By the way - concrete may have significant albedo, but it still gets way hot in bright sunlight.)

paul spencer

by paul spencer (spencerinthegorge AT yahoo DOT com) on Tue Sep 16th, 2008 at 12:31:42 PM EST
[ Parent ]
This would seem to be region specific. In colder parts of the world the warming in winter might save more energy than cooling less in summer.

It is also curious that many cultures in warm climates haven't adopted such an idea. Look at all the Mediterranean architecture in the Greek Islands or Southern Italy which have white houses, shuttered windows and other techniques to keep interiors cool, but still have dark tiled roofs. This can't all be due to a lack of suitable building raw materials.

Certainly the heat island effect in big cities increases air conditioning burdens in the summer, but that is only one side of the story.

This needs a more detailed analysis.

Policies not Politics
---- Daily Landscape

by rdf (robert.feinman@gmail.com) on Tue Sep 16th, 2008 at 09:26:35 AM EST
Actually, the analysis has been done quite heavily and while there can be limited increased energy demands during winter due to lost heat gain, the savings in summer to quite northern latitudes are quite strongly in favor of white / reflective roofing.  

This is especially clear when it comes to commercial flat roofs, which typically have low insulation values.

The work has been done ... check through the links in the diary to the Heat Island Group, for example.

Blogging regularly at Get Energy Smart. NOW!!!

by a siegel (siegeadATgmailIGNORETHISdotPLEASEcom) on Tue Sep 30th, 2008 at 03:09:44 PM EST
[ Parent ]

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