By Tyler Falk
Posting in Cities
While cities radiate with higher temperature than the rural world, the urban heat island effect might play less of a role in global warming than you might imagine.
While cities radiate with higher temperature than the rural world, the urban heat island effect plays less of a role in global warming than you might imagine.
Researchers from Stanford University have found that the urban heat island effect plays only a small part in global warming.
"Between 2 and 4 percent of the gross global warming since the Industrial Revolution may be due to urban heat islands," said Mark Jacobson, a professor of civil and environmental engineering from Stanford University who led the study. That's compared with greenhouse gases which have lead to a gross warming of about 79 percent and black carbon which has contributed about 18 percent.
But while urban heat islands might not have a large impact globally, they still contribute to local problems of air pollutions and poor health. And one cheap proposed solution, painting roofs white, does cool urban surfaces, but has a negative impact globally. Computer models show that if cities painted all their rooftops white it would results in an increase in global warming because it would reduce cloudiness.
"Cooling your house with white roofs at the expense of warming the planet is not a very desirable trade-off," Jacobson said. "A warmer planet will melt the sea ice and glaciers faster, triggering feedbacks that will lead to even greater overall warming. There are more effective methods of reducing global warming."
So what can cities do to reduce heat islands and global warming. The study says the answer might lie with rooftop solar panels. Not only do they produce electricity but they also absorb sunlight so that building materials don't.
"Photovoltaic panels do not reflect the sunlight back to the air, unlike white roofs, reflected light is not available to be absorbed again by pollutants in the air, creating heat," according to the study.
Sorry New York City, you might want to return all that white paint and make the investment in solar panels.
Oct 19, 2011
???Cooling your house with white roofs at the expense of warming the planet is not a very desirable trade-off,??? Wait, is he stating that anyone with white roofs which reflect ALL light and infrared is ALL ABSORBED in the atmosphere and NEVER is reflected back into outer space? My God! We need to melt all the ice and snow since it is ALL reflecting this heat and warming up the planet! Quick melt all those glaciers in Greenland to save the planet!
All you have to do is look at a daily summer weather forecast for Nebraska to see the impact of heat islands. Rural farms can have temps in the low 80s, small towns can hit the 90???s while the major cities just 20 miles away can break 100. There is plenty of proof that the combined impact of urban sprawl is deforestation and urban heat sinks. To say that millions of acres of concrete has no impact on average US temperatures is delusional. You also have the added impact of burning fossil fuels to keep all that development cool when those urban temperatures get into the 90s and 100s. They also make a misinformed statement that hurts their credibility. ???Photovoltaic panels do not reflect the sunlight back to the air, unlike white roofs, reflected light is not available to be absorbed again by pollutants in the air, creating heat,??? according to the study.??? Reality check guys. The best laboratory PV panels claim an unproven 40% efficiency. The best systems on the market are around 20%. The other 80% of the solar energy is manifested as heat. If you don???t believe me try putting your hand on a PV units frame on a sunny day. That???s why snow melts off them on sunny days.
...that we should all be painting our roofs and homes white to prevent global warming? And you're right @TAPhilo; We've also been previously lectured that the reduced amount of reflecting surface due to diminishing glaciers and ice shelves was supposed to be putting us into a warming death spiral. Now all of a sudden, white is bad? Oh, and let's not be remiss to mention that much of the official recorded temperature data over the last 100 years is, in fact, has been recording the effect of increased urbanization around sensor sites, and not "global warming". Either way, I plan on painting part of my roof white once I find a suitable paint to use next spring. According to these people, I'm going to destroy the planet no matter what I do, so I might as well save some money anyway.
"Quick melt all those glaciers in Greenland to save the planet!" You just made Greenpeaces hit list with that comment. LOL.
... and seemingly most of those written by Mr. Falk is to convince us that living atop each other in 'cities' is going to be 'way super cool' besides being the only way for us to house ourselves in order to save the planet. When this line of reasoning fails, and it will, look for more coercive tactics through legislation and government treaties to be proposed. It's all part of Agenda 21. Perhaps someone at SP can write an article about that.
Hates says... "To say that millions of acres of concrete has no impact on average US temperatures is delusional." Science says... "Between 2 and 4 percent of the gross global warming since the Industrial Revolution may be due to urban heat islands," Put panels on your roof. Use the electricity to cool your building on hot days. Use the panels to avoid burning fossil fuels and putting even more CO2 into the atmosphere. Greenhouse gases are the number one contributor to climate change. Soot/black carbon is the number two. Painting roofs white doesn't help as much as one would think because reflected light hits suspended carbon particles and is transformed into heat.
Your comment, " millions of acres of concrete has no impact on average US temperatures is delusional" is inaccurate. I believe you meant to say asphalt. Concrete is grey or white, depending on the mix, and therefore does not contribute to heat islands.
Concrete for this discussion can mean any paved or cemented suface that retains heat feeding a heat island.