August 15, 2012
4C Warming Coming In Megapolitan Urban Areas

Baking in the heat this summer? Population growth in urban areas promises to cause substantial warming in those "megapolitan" urban areas due to changes caused by replacing nature with buildings and roads.

TEMPE, Ariz. According to the United Nations' 2011 Revision of World Urbanization Prospects, global urban population is expected to gain more than 2.5 billion new inhabitants through 2050. Such sharp increases in the number of urban dwellers will require considerable conversion of natural to urban landscapes, resulting in newly developing and expanding megapolitan areas. Could climate impacts arising from built environment growth pose additional concerns for urban residents also expected to deal with impacts resulting from global climate change?

In the first study to attempt to quantify the impact of rapidly expanding megapolitan areas on regional climate, a team of researchers from Arizona State University (ASU) and the National Center for Atmospheric Research has established that local maximum summertime warming resulting from projected expansion of the urban Sun Corridor could approach 4 degrees Celsius. This finding establishes that this factor can be as important as warming due to increased levels of greenhouse gases. Their results are reported in the early online edition (Aug. 12) of the journal Nature Climate Change.

I think population growth is a net negative given the number of people already here. The external costs outweigh any benefits as natural resources deplete and more land gets shifted to human uses.

White roofs would cut the warming in half. But the warming would still be large.

"The worst case expansion scenario we utilized led to local maximum summer warming of nearly 4 degrees Celsius. In the best case scenario, where Sun Corridor expansion is both more constrained and urban land use density is lower, our results still indicate considerable local warming, up to about 2 degrees Celsius," Georgescu said.

An additional experiment was conducted to examine an adaptation where all of the buildings were topped by highly reflective white or "cool" roofs.

"Incorporating cool roofs alleviated summertime warming substantially, reducing the maximum local warming by about half," Georgescu said. "But, another consequence of such large-scale urbanization and this adaptation approach include effects on the region's hydroclimate."

The cool roofs, like the maximum-growth scenario without this adaptation approach, further reduce evapotranspiration water that evaporates from the soil and transpires from plants. Ultimately, comparison of summertime warming resulting from Sun Corridor expansion to greenhouse-gas-induced summertime climate change shows that through mid-century the maximum urbanization scenario leads to greater warming than climate change.

Share |      Randall Parker, 2012 August 15 10:48 PM  Climate Pollution

PacRim Jim said at August 15, 2012 11:51 PM:

Fatter people, higher temperatures.
Buy shares in power companies.

JAMES PATE said at August 16, 2012 7:31 AM:

I don't understand what a "sun corridor" is. It seems important to know in order to understand the issue here, but i have never seen the term before and it's meaning cannot be gotten from the context. Also, the article is linking this as a phenomenon which is likely to enhance the effects of AGW. One of the hotly defended tenets of AGW advocates is that there is no such thing as an Urban Heat Effect. What is being presented here and discussed is exactly Urban Heat Effect. There is an internal contradiction in the AGW paradigm apparently.

Engineer-Poet said at August 16, 2012 7:55 PM:

This is the sort of thing which might admit a technological solution.

A substantial fraction of solar radiation is invisible.  High-altitude aerostats positioned up-sun of cities might use wavelength-selective mirrors to capture much of the thermal radiation (and maybe a bit of the rest) for energy purposes, radiating the heat back to space and preventing it from reaching the ground.  Microwaves would suffice for transmitting power to the ground.  Meanwhile, the "heat island" would be cooled off by the amount of the diverted radiation.

In the winter, you'd move them around somewhat to e.g. protect snow pack from melting right away while helping cities dig out after storms.

Ronald Brak said at August 16, 2012 10:08 PM:

James, do you know anyone who says there is no such thing as an urban heat island effect? I'm not asking for a climatologist, anyone will do, butcher, baker, candlestick retailer, etc.

Russ said at August 17, 2012 7:11 AM:

Plural (anecdote) != (evidence)

But I can give you a very clear example of UHI at work. I live in Irving, TX, just to the east of DFW airport, framed by highways 183 and 114. (So you can google-map it if desired). It is absolutely routing throughout the summertime for any rain clouds moving through the area (typically from W/NW) to be cut in half like a knife by the heat island effect of the airport and surrounding construction, with rain bouncing towards our north and south. It's sufficiently strong an effect that Irving is almost never hit by tornados, though they tear through the area regularly, and suffers notably less hail damage as well (though the stuff that does make it through tends to be softball-sized monsters that can go straight through your roof).

We're scheduled for rains all this weekend if anybody gets REALLY bored and wants to see it in action real-time on a radar.

JAMES PATE said at August 17, 2012 7:35 AM:

Ah, yes, i do, that is why i pointed it out. If you want one reference, just take a look at the web site recently put up by the office of the Governor of California, concerning AGW. It is denied very explicitly. Look around, it is a hotly contested issue.

Nick G said at August 17, 2012 8:39 AM:


I believe you're thinking of temperature measurement problems caused by urban heat islands.

I think Ronald is correct - no one, including climatologists, is arguing that UHIs don't exist.

georgesdelatour said at August 17, 2012 9:11 AM:

"I think population growth is a net negative given the number of people already here. The external costs outweigh any benefits as natural resources deplete and more land gets shifted to human uses."

Won't moving people off the land enable agriculture to become more efficient? It might also be easier to protect people from heat stroke in air conditioned cities with better medical infrastructure than out in the countryside.

Phillep Harding said at August 19, 2012 2:37 PM:

Urban heat islands were initially denied. I have not been reading up on the subject recently, but the arguement had turned into "Yabutt, the weather stations (recording stations) are not located near enough to them for the heat islands to have an effect."

Anthony Watts and his supporters say that quite a few are, and had a project going to collect photos of the misplaced recording stations. They were trying to match up the recording stations used in the AGW research with the actual recording stations to determine reliability of the data and conclusions. (They were having a lot of fun being sarcastic, last I heard.)

White roofs have been unfairly (IMO) ridiculed, probably by people who don't go camping much. (Try camping in one of those old Korean War squad tents some summer and get back to me, after you recover from heat stroke.) We need something to reduce energy demand for air conditioning, and warming, and "if it's dumb but works, it's not dumb".

Engineer-Poet said at August 19, 2012 10:08 PM:

Cooling cities with reflective roofs and pavements is all well and good, but if your crops are failing because of heat waves and the oceanic food web is collapsing because the phytoplankton can't build their carbonate shells due to the reduced pH, you've got a problem.

Phillep Harding said at August 21, 2012 2:21 PM:

Did these life forms you are concerned about evolve since the beginning of the current ice age (Holocene Era, we are presently in a glacial minimum)? How did the biosphere cope during the Age of Giant Mammals?

Or the other warm era's before that?

Speaking of evolution and adaption:

I hate the heat and start melting at 65F. Just as well I'm not going to be around when this ice age ends.

Back to reducing the need for cooling, better to reduce the need for energy for active cooling (air conditioning, etc). Saves money and resources, and reduces heat produced as waste. Good thing by it's self.

Engineer-Poet said at August 26, 2012 6:07 AM:

Previously when such changes occurred, they happened over a hundred millenia.  This time they're happening over a century.  There's a limit to how fast the required pool of genetic variation required for successful adaptation can develop.

Phillep Harding said at August 26, 2012 12:07 PM:

"Hundred millenia" is 100x1000, 10^5 years. The actual time required for the change is certainly not easy to tell from the fossil record, but I've read various claims down to a mere few decades (which I'm inclined to doubt).

The most recent glacial maximum was about 2x10^4 ago, and that was only about 10^4 before the Holocene Optimum at the beginning of the present glacial minimum. 10^4 yrs for the change.

I think an opinion from a climatologist (NOT "climate scientist") or a Paleoclimatologist is called for here. Likewise an opinion from a Paleontologist for the biology part.

Ent-poiesis said at August 31, 2012 4:01 PM:

Climate has always been chaotic, with rapid changes of 10 degrees C over decadal time periods not being unusual. Compared to that, we are living in an incredibly stable climatic period.

We need to learn to adapt ourselves to a chaotic nature which is going to serve us chaos whether we are prepared for it or not. Taking a "mea culpa" stance of self-flagellation may assuage our consciences in a perverse way, but it is completely divorced from reality.

Phillep Harding said at September 9, 2012 9:29 AM:

Ent, the majority might be falling for that "it's all our fault".

However, (IMO: "Obviously") the brains behind it are today's witch doctors and cult leaders, with the same motivation as witch doctors and cult leaders have had for thousands of years: "Invent or create a crisis, rationalize a solution that benefits the con artist." (Chicken Little variant where the fox encourages Henny-Penny to go terrify the other fowl into taking shelter in the fox's lair.)

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