Coolest Notions Pay Off

When it comes to high-tech possibilities for counteracting climate change, the headlines tend to focus on the seemingly sci-fi stuff: brightening clouds, pumping particles into the stratosphere and launching giant mirrors into space.

But there are down-to-earth versions of the same basic concept, approaches as simple as painting roofs white or using light-colored pavement to cast away more heat from the Earth. A group at Lawrence Berkeley National Laboratory is exploring how big an impact this approach could have on global warming, as well as developing next-generation building materials that could reflect more light.

Compared with more unconventional strategies, the advantages of white roofs and related concepts are that they're proven, cheap and relatively noncontroversial. Indeed, the basic idea has been employed in sweltering parts of the world since at least the time of the pharaohs.

"It's so saleable that people tend to smack their heads and say, 'Why didn't I think of that?'" said Arthur Rosenfeld, distinguished scientist emeritus in the environmental energy technologies division at Lawrence Berkeley, who is working with the lab's Heat Island Group. "There's a huge payoff."

Warming Offset

Indeed, if all "eligible" flat urban roofs worldwide were whitened, it could reflect away enough heat to offset the warming effect of 1.2 gigatonnes of carbon dioxide each year, according to research at the Heat Island Group. That's roughly one-thirtieth of annual global emissions.

It could also chip away at total greenhouse gas emissions, since those cooler buildings wouldn't use as much energy for air conditioning.

The total impact is far from the level theoretically promised by things like cloud brightening or spraying sulfur particles into the stratosphere. Done on a large enough scale, using machines under development to whiten clouds along coastlines could offset the warming effect from a doubling of carbon dioxide concentrations in the atmosphere, according to some studies.

But making roofs white can be done today, without the risks and uncertainties associated with more audacious approaches.

Moreover, what's abundantly clear to anyone studying climate change is that there are no silver bullets. Effectively confronting the enormous challenge of global warming will demand a wide range of responses: aggressively expanding clean-energy options, rapidly developing more efficient alternatives, enacting laws that discourage greenhouse gas emissions and quite possibly using "geoengineering" options for sucking greenhouse gases out of the sky or reflecting away heat.

"Almost every potential step we take is a partial solution," said Ronnen Levinson, the staff scientist who leads the Heat Island Group. "White roofs can by no means reverse global warming, but the cooling benefit is substantial and it's something that's easily within reach."

Carbon Dioxide Dissolves

An important caveat: Whitening roofs doesn't directly remove carbon dioxide from the atmosphere, so other dangerous consequences of rising greenhouse gases levels remain, notably ocean acidification. The CO₂ dissolved in oceans, lakes and rivers can harm critical components of underwater ecosystems, including coral reefs and plankton.

But curbing heat itself will become increasingly critical, with global average temperatures set to soar this century. Making all flat roofs white would be equivalent to taking half the world's cars off the roads, in terms of the warming effect of CO₂

There are other big advantages to cool roofs, including reducing energy use, smog and illnesses associated with poor air quality. Indeed, these were the original problems that the Heat Island Group, formed in 1979, sought to address. Roofs and pavements constitute about 60 percent of the surface area of cities, so they absorb far more sunlight than rural areas dominated by vegetation.

That additional heat forms smog that undermines public health and leads residents and building owners to crank up their air conditioning.

State Building Rules

Cool roofs also save lives.

A 1995 Chicago heat wave killed at least 739 people - and the highest-risk group lived on the top floors of buildings with black roofs. White roofs can stay up to 60 degrees cooler than traditional ones under a baking summer sun.

That's a critical consideration as global warming increases the frequency and intensity of heat waves. The one that scorched much of Europe during the summer of 2003 reportedly killed more than 50,000 people.

That event was the turning point for Rosenfeld. As a member of the California Energy Commission at the time, he helped push through new building standards in 2005 requiring new or remodeled flat roofs on commercial buildings in the state to be white.

The rules have slowly begun to change the complexion of California's cities. The Heat Island Group shows off before-and-after aerial photos of San Jose that reveal an unmistakable lightening over the course of just a few years.

But flat roofs are an easy target. It was a relatively simple sell as public policy goes, because it lowered energy costs for building owners without requiring them to pay much, if anything, more. There is also no aesthetic downside, because few see the top of flat roofs.

The same, however, can't be said for the sloped roofs of most residential homes. Indeed, few things would get homeowners associations upset faster than a white roof - save perhaps a pink one.

That's one reason the Heat Island Group, with the support of the Department of Energy, is developing roofing materials that look like conventional dark red or brown shingles, yet reflect back more heat.

Cooler Playgrounds

The trick is using materials, such as titanium dioxide, that cast back more light in the near infrared spectrum. Our eyes can't perceive that light, but it makes up about half of the energy in the sunlight that reaches the Earth.

The Berkeley Lab is also collaborating with industry to develop cool versions of both asphalt concrete and cement concrete pavements. On a summer day, the cool pavement in its parking lot can run about 30 degrees cooler than adjacent blacktop.

As of 2008, new or remodeled residential buildings in some of the hottest areas of the state must also have cool colored roofs, making California's rules the strictest in the nation, possibly the world.

There are also energy-efficiency grants for certain government structures like schools that opt to use cool building materials. That's why the students at King Elementary School in Richmond spend recess playing on a light-colored playground.

Canceling out those 1.2 gigatonnes of carbon dioxide annually required only flat urban roofs. Add in sloped roofs and pavement, which makes up about half of the traditionally "dark" areas of cities, and the potential shoots up considerably. Include the fact that reducing the need for air conditioning also cuts down on actual CO{-2} emissions, and it goes higher still.

Free market economics should get more consumers, companies and government agencies to adopt light colors and cool materials, as they see the cost benefit of lowering their energy bills.

But it will almost certainly require rules that mandate or offer incentives for such practices - tax credits, energy incentives, building codes and more - to get anywhere near all eligible flat urban roofs worldwide, to say nothing of all roofs and pavement generally.

Fortunately some of that work is slowly moving forward.

Outgoing Energy Secretary Steven Chu, previously the director at Lawrence Berkeley, pushed the cool roofs idea throughout his tenure in the Obama administration. He issued a memorandum in 2010 directing Department of Energy sites to install cool roofs whenever it was cost-effective at the time they were being replaced - and encouraged other federal agencies to do the same.

The Clean Energy Ministerial, a forum for G-20 nations focused on promoting sustainable energy first hosted by Chu, set up a working group in 2011 to craft policies to increase the "solar reflectance of urban surfaces" around the world.

The American Society of Heating, Refrigeration and Air-Conditioning Engineers, which sets the national model codes that states and cities often adopt as mandatory rules, first put cool roof standards for flat-roofed buildings into effect for certain regions back in 2007. An update due next year will widen that area to include Washington, Philadelphia and New York.

Meanwhile, programs like Energy Star, the Cool Roof Rating Council and the U.S. Green Building Council's Leadership in Energy and Environmental Design have been setting reflectance ratings for building products and techniques, all of which encourage more consumers and developers to consider cool materials.

Expanding Scope

As advocates point out, there's nothing saying this effort has to stop with buildings. Cars, trucks and trains - as matter of fact, just about any man-made object that sits under the sun - are all fair game for whitening.

Chu underscored that in the summer of 2011, when he posted a picture on his Facebook page of a white-capped UPS truck driving around the nation's capital.

"An encouraging sight," he wrote. "If UPS can set aside its trademark brown color scheme for the sake of a cooler cargo area, hopefully more businesses and consumers will begin to ask themselves: 'What can white roofs do for you?'"