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White Roofs May Actually Add to Global Warming

By Douglas Main | October 20, 2011 8:53 am

A new study published in the Journal of Climate claims that painting rooftops white—a method championed by energy secretary Steven Chu and others to combat climate change—only minimally reduces local cooling, and actually causes a slight increase in overall global warming.

How the Heck:

  • The researchers used a global climate model called GATOR-GCMOM [PDF], which incorporates a host of data from satellites and weather stations worldwide. It models how relationships between various environmental conditions, like the presence of clouds or pollutants, will affect local and global climate.
  • The model found that more white roofs means less surface heat in cities (which is obvious enough to anyone who’s sat in a car with a black interior in the sun). Lower local temperature means less water evaporates and rises up to eventually form clouds, says lead author and Stanford University researcher Mark Jacobson. The decrease in clouds allows more sunlight to reach the Earth’s surface, leading to higher temperatures overall.
  • The model also predicts that much of the light reflected by rooftops will eventually be absorbed by dark carbon soot and particulates that are especially prevalent in the air above urban areas. This could limit local cooling and cause warming elsewhere as the particles drift away.

Not so Fast:

  • One possible benefit to white roofs is the reduction of cooling costs for the buildings painted white, which isn’t explicitly addressed in this paper. This could make the practice useful in warmer climates, but at least one study has found that a switch to white roofs wouldn’t lead to energy savings on a global scale.
  • The study didn’t calculate how the change would impact energy use, or how such a change could impact emissions and their effect on climate.
  • Even with switch to 100% white roofs, the predicted increase in global temperature (0.13 F over 20 years) is quite small, and dwarfed by expected effects of greenhouse gases and carbon soot.
  • Data generated by this model are preliminary, as with any computer simulation of a system as vastly complicated as Earth’s climate, and the matter is far from settled. Other researchers stand by their own calculations that white roofs can provide energy savings in a variety of climates and reduce heating of the Earth’s surface.

To Paint or Not to Paint:

  • Jacobson speculates that any energy savings in white-roofed buildings would be eaten up by increased energy use elsewhere (i.e., for cooling) from overall warming caused by white roofs. So it’s probably not a great measure for widespread use, he says. But in a warm, sunny climate, a white roof almost certainly doesn’t hurt on an individual basis and may help reduce the need for air-conditioning (as inhabitants of sultry climes have known for a long time).
  • Conversion to white roofs is a bad idea globally, Jacobson says. Instead, if you want to make a difference, install a photovoltaic system or solar panels on your roof, which reflects light and also generates clean electricity.

Reference: Mark Z. Jacobson and John E. Ten Hoeve. Effects of Urban Surfaces and White Roofs on Global and Regional Climate. Journal of Climate. 2011. DOI: 10.1175/JCLI-D-11-00032.1

Image: Christopher Dick / Flickr


MORE ABOUT: albedo, climate, climate model, global warming, heat island, stanford, urban heat island, urban heat island effect, white roofs

Melting glaciers, from Greenland to Antarctica, have become symbols of global warming — and monitoring their retreat is one major way scientists are keeping tabs on the progress of climate change.

Now, scientists are trying to bring the issue a little closer to home by using time-lapse photos to show the effects of climate change are already occurring.

A paper published last week by the Geological Society of America presents dramatic before-and-after photographs of glaciers around the world over the last decade. Most of the photos were taken by photographer James Balog as part of a project called the Extreme Ice Survey, which began documenting changing glaciers around the world in 2007. The project was featured in the 2012 documentary “Chasing Ice.”

Below is a time-lapse video, using images captured by Balog and the Extreme Ice Survey team, documenting changes at Mendenhall Glacier in Alaska. Between 2007 and 2015, the glacier retreated by 550 meters, or more than 1,800 feet.

Photojournalist James Balog and the Extreme Ice Survey team travels the world to document vanishing ice. (Earth Vision Institute/ Extreme Ice Survey)

On-the-ground expeditions are “key to informing broad audiences of non-specialists,” note the paper’s authors, who include Balog and multiple other glacier and climate experts. “Science is grounded in observation, so science education will benefit from displaying the recently exposed landscapes.”

In an interview with The Washington Post, Balog suggested that ground-level photographs provide an immediacy that’s missing from other scientific tools, such as satellite images.

“I do think that our most dominant sensory apparatus is our vision,” he added. “So when you can deliver an understanding of the reality of what’s going on through vision, rather than numbers or maps, that also has the unique ability to touch and influence people.”

Below are before-and-after images of Switzerland’s Stein Glacier, which also retreated by 550 meters between 2006 and 2015.

Stein Glacier, in part of the Swiss Alps, on Sept. 17, 2011. (James Balog and the Extreme Ice Survey/GSA Today/Geological Society of America)

Stein Glacier on Aug. 20, 2015. (James Balog and the Extreme Ice Survey/GSA Today/The Geological Society of America)

For Balog, the location that’s had the greatest personal impact is Sólheimajökull Glacier in Iceland, which he described as his “first love.”

“It’s where I kind of first realized how quickly the ice is changing,” he said. “And it’s because of what the local scientists were able to show me by way of the change in the glacier in a shockingly short period of time.”

Reports suggest that the glacier has shrunk by more than 2,000 feet since 2007. Below is a time-lapse of its retreat between 2007 and 2015.

Photojournalist James Balog and the Extreme Ice Survey team travels the world to document vanishing ice. (Earth Vision Institute/ Extreme Ice Survey)

While the Greenland and Antarctic ice sheets often receive the most press — and not without reason, thanks to the sheer amount of ice they contain — Balog’s photos include smaller mountain glaciers from places like Alaska and Europe. In many places around the world, these smaller glaciers are responding even more rapidly to their changing environments than their polar counterparts.

And while the Greenland and Antarctic ice sheets may have the greatest long-term potential to raise global sea levels, melting mountain glaciers come with their own set of consequences as well. Nearby communities often rely on runoff from these glaciers for sources of fresh water. But as the glaciers shrink away, less water becomes available. Some experts have also raised the possibility that melting mountain glaciers could result in huge floods capable of destroying nearby homes and infrastructure.

“People who live in proximity to these things are really are quite acutely aware of how much things are changing and think about it, and the researchers in their areas study it,” Balog said. “These are important and immediate impacts.”

Below is Trift Glacier, which retreated by more than 3,700 feet between 2006 and 2016.

Trift Glacier in the Swiss Alps in 2006. (James Balog and the Extreme Ice Survey/GSA Today/The Geological Society of America)

Trift Glacier on Aug. 20, 2015. (James Balog and the Extreme Ice Survey/GSA Today/Geological Society of America)

Satellite measurements still provide some of the most precise information on glacial retreat all over the world, revealing the vulnerability of the Greenland and West Antarctic ice sheets. Scientists have used satellite data to estimate how much ice these sheets contain in total. (If the Greenland and Antarctic ice sheets melted away entirely, for instance, they could raise sea levels by more than 200 feet. But it would take tens of thousands of years for that to happen, even at current warming rates.)

On-the-ground imagery provides a different kind of service, presenting compelling visual evidence of the climate effects that are already occurring. And the photos have an added visceral effect because they come from places where human communities exist — it’s not just ice on deserted Antarctica that’s disappearing, but also glaciers from Europe and the Americas to Asia and Africa. And once they’re gone, they may never exist again.

“It is likely that these recently deglaciated landscapes will not be re-occupied by ice during foreseeable human timeframes,” the paper’s authors warn. “In other places, forests or other vegetation may rapidly colonize such landscapes. Photographic records, such as those included here, provide an outstanding avenue for education, because they display a record of ice that may never be seen again.”

More at Energy and Environment:

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