Washingtons Blog
Whether you are worried about global warming, a new ice age, or just want to save on your electric bill … here’s a big part of the answer.
Everyone knows that – on a hot day – you stay cooler in light clothes than dark clothes.
We know that dark colors get warmer than light ones.
That’s because light colors reflect sunlight, while dark ones absorb it. That’s why solar panels are always black: it helps collect the sun’s energy.
This is one of the untapped keys for handling climate change.
As the Independent noted Friday:
Painting roofs white and using light-coloured materials to surface roads and pavements would not only make cities cooler in summer, it would save the same amount of carbon as taking all the cars in the world off the roads for 50 years, a study has found.
One of the simplest, yet most effective, ways of engineering the urban environment to cope with global warming is to increase the reflectivity of the cityscape so that more of the incoming sunlight is directed back into space, scientists said.
City buildings in warm climates with “cool coloured” surfaces that reflect infra-red radiation would also be cooler than traditional buildings and so would conserve energy – and carbon – that would otherwise be used on air conditioning.
Increasing solar reflectance or “albedo” has been suggested as a way of combating the “heat island” effect of towns and cities, where summers are made unbearably hotter in built-up areas by Tarmac roads and dark buildings that absorb sunlight.
Two years ago, Barack Obama’s top man on global warming, Professor Steven Chu, the US Secretary of Energy, suggested at the Royal Society in London that one of the most effective engineering measures to tackle rising temperatures is to paint roofs.
“If the building is air-conditioned, it’s going to be a lot cooler, it can use 10 or 15 per cent less electricity… you also do something in that you change the albedo of the Earth – you make it more reflective,” Professor Chu said. Now scientists, led by Professor Hashem Akberi, of Concordia University in Canada, have studied this in detail and found that it can have a significant impact.
They estimate that a city or town where the roofs and the pavements and roads have light-coloured surfaces can increase their albedo by about 10 per cent, which globally would provide a CO2 offset of between 130 billion and 150 billion tonnes – the same as taking every car in the world off the road for 50 years.
“Increased albedo can decrease atmospheric temperature and counter some of the anticipated temperature increases from global warming,” the scientists say in the journal Environmental Research Letters.
Albedo is measured on a scale of zero to one, where 1.0 is totally reflective and zero absorbs all sunlight.
The researchers believe that it would be cheap and easy to increase the albedo of cities by applying the reflective materials when roofs and roads are routinely resurfaced, rather than doing it as a special measure
Last year, Juan Carlos Pineiro Escoriaza wrote in Reuters:
Painting black tar roofs with a white, solar-reflective coating is a low cost, quick and tangible way to reduce the risk of power grid ‘brown-outs’, save millions of dollars in energy costs, and curb climate change. The statistics are as simple as they are staggering: A roof covered with solar-reflective white paint reflects up to 90% of sunlight as opposed to the 20% reflected by a traditional black roof. On a 90°F day, a black roof can be up to 180°F. That heat has a major impact on interior building temperature, potentially heating your room to between 115 – 125°F. A white roof stays a cool 100°F. Plus the inside of the building stays cooler than the air outdoors, around 80°F in this example, reducing cooling costs.
White roofs also reduce the “urban heat island” effect in which temperatures rise in dense urban areas because of the proliferation of heat-radiating, black tar surfaces. For example, the Urban Heat Island effect causes New York City to be about 5 degrees warmer than surrounding suburbs and accounts for 5 to 10 percent of summer electricity use.
In New York City alone, 12% of all surfaces are rooftops. It’s estimated that implementing a white roof program in 11 metropolitan cities could save the United States 7 gigawatts in energy usage. That’s the equivalent of turning off 14 power plants, and a cost savings of $750 million per year.
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If we were to coat 5 percent of rooftops per year worldwide, we would be finished by 2030. This would save the U.S. 24 billion metric tons in CO2. That happens to be exactly how the world as a whole emitted in 2010. So, in essence, this would be like turning the world off for an entire year — while also saving some money on the energy bills while doing it.
But many top scientists and government agencies have worried for over a 100 years that the real danger is a new ice age … not global warming.
Couldn’t painting all of the roofs and roadway surfaces white accelerate any cooling trends which threaten to freeze us?
Not if we are smart.
The whole idea is to be able to adapt to whatever conditions come our way. Specifically, it would be simple to install roofs which change from light to dark – and back – based upon the temperature … or at the flip of a switch.
We’ve got “electronic curtains” that go from clear to dark depending on whether the electric circuit is feeding them power.
Scientists have created materials that change to any color you want through the use of a magnetic field. As Popular Science noted in 2009:
In the future, signs will be instantly rewritable and walls will change color at the flip of a switch. A research team at the University of California at Riverside has created a new magnetically activated, instantly and reversibly color-changing material with potentially groundbreaking applications. The technology is based on that used by colorful birds, beetles, and butterflies: instead of static pigments, the material employs “structural color,” which depends on the interference effects of light.
Although other methods for creating tunable structural color exist, their color-changing processes are slow and complicated, and involve internal adjustments. This new material is composed of microscopic polymer “magnetochromatic microspheres,” or beads, whose structural stability allows for instant changes in color with “no change in the structure or intrinsic properties of the microspheres themselves,” according to Yadong Yin, who led the study.
The beads’ colors change in response to magnetic fields, which alter the relative orientation of the periodic arrays within them. This use of magnetic fields allows for “instant action, contactless control, and easy integration into electronic devices already in the market.”
The color-changing beads can also be used to create environmentally friendly pigments for inks and paints. Yin, an assistant professor of chemistry, and his colleagues, plan to work next on the wide array of applications for which this material is so promising. “Rewritable energy-saving display units such as papers and posters are our main interests,” says Yin in the announcement. “We will also try to develop a similar new material for chemical and biological sensors.”
Indeed, in 2009, MIT graduates created roof tiles which do exactly what is needed … change colors depending on temperature:
The ideal situation … would be to get the advantage of white roofs when it’s hot and black roofs when it’s cold.
Now, there may be a way to have both. A team of recent MIT graduates has developed roof tiles that change color based on the temperature. The tiles become white when it’s hot, allowing them to reflect away most of the sun’s heat. When it’s cold they turn black and absorb heat just when it’s needed.
The team’s lab measurements show that in their white state, the tiles reflect about 80 percent of the sunlight falling on them, while when black they reflect only about 30 percent. That means in their white state, they could save as much as 20 percent of present cooling costs, according to recent studies. Savings from the black state in winter have yet to be quantified.
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They use a common commercial polymer (in one version, one that is commonly used in hair gels) in a water solution. That solution is encapsulated — between layers of glass and plastic in their original prototype, and between flexible plastic layers in their latest version — with a dark layer at the back.
When the temperature is below a certain level (which they can choose by varying the exact formulation), the polymer stays dissolved, and the black backing shows through, absorbing the sun’s heat. But when the temperature climbs, the polymer condenses to form tiny droplets, whose small sizes scatter light and thus produce a white surface, reflecting the sun’s heat.
They are now working on an even simpler version in which the polymer solution would be micro-encapsulated and the tiny capsules carried in a clear paint material that could be brushed or sprayed onto any existing surface. The tiny capsules would still have the color-changing property, but the surface could easily be applied over an existing black roof, much more inexpensively than installing new roofing material.
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Because the materials are common and inexpensive, team members think the tiles could be manufactured at a price comparable to that of conventional roofing materials — although that won’t be known for sure until they determine the exact materials and construction of their final version.
So if those worried about global warming are right, the color-changing roof materials will help. And if those worried about global cooling are right … the color-changing roof materials will help as well.
Isn’t that what a species which hopes to stick around for many thousands of years - no matter what the climate is doing – needs?
