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City Temps May Soar From Urbanization, Global Warming

For scientists who worry about climate change, cities are just plain annoying. The acres of asphalt that cover roads and parking lots and roofs absorb enormous amounts of heat. In the summer, whirring air conditioners channel even more heat out of buildings and into the air. Climate scientists have to subtract this so-called urban heat island effect from their calculations if they want to get a true picture of how greenhouse gas emissions are warming the planet.

For people who actually live in cities, however the urban heat island effect is more than just a mathematical annoyance. If you’re sweltering on a hot summer day, your body doesn’t much care where the heat is coming from. And according to a paper just published in Nature Climate Change, urbanization alone could drive local temperatures up by a whopping 7°F by 2050 in some parts of the U.S. — some two or three times higher than the effects of global warming (which would also be going on at the same time).

“If you average this over the whole globe, the effect will be zero,” said lead author Matei Georgescu, of Arizona State University, in an interview. “But people don’t care about global temperatures. They care about conditions where they live.”

In this case, the people live in Arizona’s Sun Corridor, a megalopolis, or band of urbanization, which stretches from the city of Nogales on the Mexican border to Prescott, about 100 miles north of Phoenix. It’s one of the fastest-growing areas in the country, with up to 16 million residents expected by 2050.

All those people will need roads and roofs and places to live, so Georgescu and several colleagues wondered what the urban heat island effect of all that additional population might be. They discovered that nobody had really thought much about it. “This is an absolutely under-researched area,” Georgescu said, “and it deserves much more attention.”

Georgescu and his team took urbanization maps created by Maricopa Association of Governments and computerized weather prediction models that take the urban heat island effect into account, and put them all together to figure out where local temperatures might be heading. They focused on summer, when the urban heat island effect is strongest, and when high temperatures can be downright deadly, especially to the elderly who are already suffering from cardiovascular disease, lung diseases or diabetes.

The danger is especially great when nighttime temperatures remain high, which keeps the body from recovering after a scorching day. Unfortunately, the urban heat island effect affects nighttime temperatures the most: that’s when all the heat absorbed by the roads and buildings is re-released.

Georgescu emphasized that the 2050 scenario of a 7°F increase is the worst case: if population growth is more restrained, or if urban planners keep local population densities low and undeveloped open space relatively high, the effect could be much less. Reining in emissions of greenhouse gases would also make a difference. And the simple solution of replacing dark, heat-absorbing asphalt roof shingles with white, reflective roofs could cut the projected temperature increase.

“It’s possible, it’s practical, and it could cut the projected temperature increase in half,” Georgescu said. Unfortunately, he added, it doesn’t help at all with another urbanization-related problem. When you pave or build over undeveloped land, you seal in whatever moisture there is in the soil. It can no longer evaporate, which cuts off an important source of humidity, and ultimately, of rain.

“So one of our take-home messages,” he said, “is that to be truly sustainable, you can’t just focus on temperatures. The climate system isn’t only about warming.”


By Petr Jandacek (Los Alamos, NM 87544)
on August 15th, 2012

People in CASABLANCA and in Los Alamos’  White Rock neighborhood learned about the virtues of “reflecting white” a very long time ago.  Supply & Demand forces indicate that white parasol market will be on the rise in the future.

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By No Thanks
on August 15th, 2012

Account for buildings and asphalt….what a novel idea! ....Oh wait, a global warming skeptic UC Berkeley professor just did precisely that study.

And guess what? He converted to being a believer in global warming.

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By Greg (Fairfax, VA)
on August 15th, 2012

Doesn’t this mean that the extra heated and dry air rising up and blowing away from the cities will alter weather patterns and rain fall amounts many miles from the urban core? I’m an urban gardener. Where I live in Fairfax County, Virginia we are vexed with dryer conditions than the rest of the county. Meteorologist actually study the phenomenon and call our area of the county “the dry slot”. They think the rain fall patterns are being altered by all the development along Rt. 66. Time and again I’m witnessed on Doppler Radar a large band of precipitation approaching our area and as the rainfall gets closer it splits into two sections. One heads northward towards Rockville/Bethesda, Maryland area and the other heads southward to lands beyond Alexandria. It’s like the rain headed for “the Dry Slot” just evaporated before it could reach us. This is so discouraging to a man who likes to grow plants, so I am moving out of the dry zone next year.

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By Byron Smith (Edinburgh)
on August 15th, 2012

White roofs, yes. But also green roofs.

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By Simon Moltz (Floresville Texas 78114)
on August 15th, 2012

The world is a closed system; icebox of old; the polar ice caps and glacers it’s coolant.  We use airconditioners which
doump vast amounts of heat in to the air. Burn gas in automobeals which doump vast amounts of heat in to the atmosphere.
Co2 acts as a blanket to keep the heat in. All this is accerelating the warming effect.  But the actual warming began long ago
when Cantral Pard was under ice.  It is my opion we are going to have to adjust and adapt to the new climate.

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By Mike Haseler (Scotland)
on August 17th, 2012

In the UK there are 23,000 extra deaths each winter. In the worst summer on record (2003) there were ..... 2,300 deaths.

So, once in a blue moon there is a summer which is 10% as bad as the average winter. And in the last couple of winters because it was so bad, there are estimates of around 40,000 deaths.

To put that in context, over the next 100 years, there will be 2.3million extra winter deaths in the UK.

Going back, in the 1690s it is estimated that a quarter of Scotland’s population died from cold in a period known as the “Maunder Minimum”. This was a time of low solar activity. Recent work at CERN has shown there is strong scientific evidence to support a link between solar activity and climate so it is very likely the low solar activity was at least partly if not mainly to blame for the deaths in Scotland.

... scientists now suggest we are entering a new period of low solar activity!

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By PaulR
on August 18th, 2012

I cant believe the hype. If the government subsidises it - it is worthless! NOT viable.

Since man made global warming is not a problem due to the fact that the Woods experiment approx 100 years ago showed the greenhouse effect to be virtually non existent and this is verified by Prof Nasif Nahles similar repeat of the woods experiment who also showed why Pratts experiment failed!

I can only deduce that this ecological craze is financed with ulterior motives in mind that are non genuine in nature.
What can be expected from the religious though!

Before putting the environment in order would it not be more useful to put economics - banking, government, industry and the runaway legal system in order first !

I see nothing useful here!

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By mlemonick
on August 18th, 2012

PaulR makes the rather shocking claim that the greenhouse effect has been “shown to be virtually nonexistent.” He should know that a vast majority of even those people who consider themselves global warming skeptics would find this to be a nonsensical statement.

Mr R. might also want to avoid driving on interstate highways, which are subsidized by the government, or flying in planes, since the air traffic control system and the airports themselves are subsidized by the government. Neither of these, per Mr. R., is viable. So presumably, they don’t exist. Or…something.

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By Gwen (Austin, TX 78703)
on September 25th, 2012

The density of cities provides many benefits that may outweigh [the current impact of] the urban heat island effect.  Increased FAR in CBD’s vs. miles of paved roads, crowded highways, gasoline gobbled, and the further desecration of natural areas required to support edge cities, fringe, or edgeless cities, and everyday suburban sprawl is a no brainer. 

New energy codes are starting to address issues of reflectivity vs. heat absorption, run-off, & other dense development concerns.  Architects, designers, engineers, developers, gardeners, and municipalities are leading the charge to green rooftops, “plant walls”, return asphalt to dirt, & discourage single occupancy vehicles.  Some of the urban heat island effects can be readily reduced; now we need to take the next hard steps!

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By Bruce Sorrell (Fairfax Station, VA 22039)
on October 8th, 2012

Just wanted to second the complaint voiced by Greg (Fairfax, VA) on August 15, 2012).  We’re in Fairfax Station, just NW of the Woodbridge/Lorton area.  Like Greg, we try to garden and I’m also an avid BBQ addict.  Both hobbies have us heavily dependent on the weather.  I can’t tell you how many times I’ve put off watering the yard or firing up the grills because of a rain forecast that didn’t produce a single drop for our locale.  I regularly see rain training SW to NE on the radar, but more often than not it falls to the west of us and to the east.  It’s like we have our own private weather system…Death Valley - East.  Can anyone verify Greg’s hypothesis as to why we’re so rain deprived ?  I’m not ready to move, but I’ve surely given up on our weather forecasts !  Slainte!

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