Satellites Image the Urban Heat Islands in the Northeast

Gee where have we seen something like this before? Dads/Moms and Grandparents: if you’d like your children/grandchildren to be able to do something on UHI for the spring science fair, here’s an easy to do idea. – Anthony

From Science @ NASA.gov – Satellites Pinpoint Drivers of Urban Heat Islands in the Northeast

Providence, R.I. Providence, RI, in natural color, infrared, vegetation and developed land

Cities such as New York, Philadelphia, and Boston are prominent centers of political power. Less known: Their size, background ecology, and development patterns also combine to make them unusually warm, according to NASA scientists who presented new research recently at an American Geophysical Union (AGU) meeting in San Francisco, Calif.

Summer land surface temperature of cities in the Northeast were an average of 7 °C to 9 °C (13°F to 16 °F) warmer than surrounding rural areas over a three year period, the new research shows. The complex phenomenon that drives up temperatures is called the urban heat island effect.

Heat islands are not a newly-discovered phenomenon. Indeed, using simple mercury thermometers, weather watchers have noticed for some two centuries that cities tend to be warmer than surrounding rural areas.

Likewise, researchers have long noticed that the magnitude of heat islands can vary significantly between cities. However, accurate comparisons have long eluded scientists because ground-based air temperature sensors tend to be unevenly distributed and prone to local bias. The lack of quantifiable definitions for urban versus non-urban areas has also hindered comparisons.

Satellite technology, which offers a more uniform view of heat islands, is in the process of changing this. The group of researchers from NASA’s Goddard Space Flight Center in Greenbelt, Md., presented results based on a new method for comparing heat islands at the AGU meeting.

Providence, R.I. Providence, RI, in natural color, infrared, vegetation and developed land

Visible Light Surface Heat Developed Land Vegetation Cover
› Larger image › Larger image › Larger image › Larger image

Buffalo, N.Y. Buffalo, NY, in natural color, infrared, vegetation and developed land

Visible Light Surface Heat Developed Land Vegetation Cover
› Larger image › Larger image › Larger image › Larger image

Satellite-produced maps of Providence and Buffalo highlight the role that differences in development patterns and vegetation cover can have on the magnitude of a city’s urban heat island. Though the two cities have the same approximate size, Providence has a significantly stronger heat island. Credit: NASA/Earth Observatory

› Larger images of Providence

› Larger images of Buffalo

“This, at least to our knowledge, is the first time that anybody has systematically compared the heat islands of a large number of cities at continental and global scales,” said Ping Zhang, a scientist at Goddard and the lead author of the research.

urban heat island graphic

Land surface temperatures in cities, particularly densely-developed cities, tend to be elevated in comparison to surrounding areas — a phenomenon called an urban heat island. Credit: NASA

› Larger image

mortality and temperature graph from 2003 Paris heatwave

Heat islands can be deadly. This graph shows how the number of deaths spiked in Paris during a sweltering heat wave in 2003. Credit: University of Hawaii at Manoa/Benedicte Dousset

› Larger image

heat island graph estimating the impact of air conditioning

Air conditioning systems release waste heat into the atmosphere such that their widespread use can inadvertently elevate city air temperatures. This graph shows the result of a model that calculated the likely magnitude of the effect during the 2003 heat wave in Paris. Credit: Météo France/Cécile de Munck

› Larger image

day vs. night effects of the heat island

Surface temperatures vary more than air temperatures during the day, but they both are fairly similar at night. Credit: EPA

› Larger image Development produces heat islands by replacing vegetation, particularly forests, with pavement and other urban infrastructure. This limits plant transpiration, an evaporative process that helps cool plant leaves and also cools air temperatures, explained Robert Wolfe of Goddard, one of the scientists who developed the method.

Dark city infrastructure, such as black roofs, also makes urban areas more apt to absorb and retain heat. Heat generated by motor vehicles, factories, and homes also contributes to the development of urban heat islands.

A New View

The new method for comparing cities, which the team of scientists has honed for about two years, involves the use of maps of impervious surface area produced by a United States Geological Survey-operated Landsat satellite, and land surface temperature data from the Moderate-resolution Imaging Spectroradiometer (MODIS), an instrument aboard NASA’s Aqua and Terra satellites.

Impervious surfaces are surfaces that don’t absorb water easily, such as roads, roofs, parking lots, and sidewalks. Land surface temperatures tend to be higher and more variable than air temperatures, but the two generally vary in sync with each other.

By analyzing data from thousands of settlements around the world, the Goddard team has pinpointed key characteristics of cities that drive the development of heat islands. The largest cities, their analysis shows, usually have the strongest heat islands. Cities located in forested regions, such as the northeastern United States, also have stronger heat islands than cities situated in grassy or desert environments.

Most recently, the Goddard group has shown that a city’s development patterns — whether a city is sprawling or compact — can also affect the strength of its heat island.

By comparing 42 cities in the Northeast, they found that densely-developed cities with compact urban cores are more apt to produce strong urban heat islands than more sprawling, less intensely-developed cities.

The compact city of Providence, R.I., for example, has surface temperatures that are about 12.2 °C (21.9 °F) warmer than the surrounding countryside, while similarly-sized but spread-out Buffalo, N.Y., produces a heat island of only about 7.2 °C (12.9 °F), according to satellite data. Since the background ecosystems and sizes of both cities are about the same, Zhang’s analysis suggests development patterns are the critical difference.

She found that land cover maps show that about 83 percent of Providence is very or moderately densely-developed. Buffalo, in contrast, has dense development patterns across just 46 percent of the city. Providence also has dense forested areas ringing the city, while Buffalo has a higher percentage of farmland. “This exacerbates the effect around Providence because forests tend to cool areas more than crops do,” explained Wolfe.

Cities in desert regions, such as Las Vegas, in contrast, often have weak heat islands or are actually cooler than the surrounding rural area. Providence, R.I.; Washington, D.C.; Philadelphia, Pa.; Baltimore, Md.; Boston, Ma.; and Pittsburgh, Pa.; had some of the strongest heat islands of the 42 northeastern cities analyzed.

“The urban heat island is a relative measure comparing the temperature of the urban core to the surrounding area,” said Marc Imhoff, the leader of the Goddard research group. “As a result, the condition of the rural land around the city matters a great deal.”

Heat Island Impacts

Ratcheting up temperatures can have significant — and deadly — consequences for cities. Heat islands not only cause air conditioner and electricity usage to surge, but they also increase the mortality of elderly people and those with pre-existing respiratory and cardiovascular illness.

The U.S. Environmental Protection Agency estimates that, between 1979 and 2003, heat exposure has caused more than the number of mortalities resulting from hurricanes, lightning, tornadoes, floods, and earthquakes combined.

“It is the lack of cooling at nighttime, rather than high daytime temperatures, that poses a health risk,” said Benedicte Dousset, a scientist from the University of Hawaii who also presented data about heat islands at the AGU meeting.

Dousset recently analyzed surface temperature images of Paris and showed the spatial distribution of heat-related deaths during a sweltering heat wave in 2003. Some 4,800 premature deaths occurred in Paris during the event, and excess mortality across Europe is thought to be about 70,000.

The risk of death was highest at night in areas where land surface temperatures were highest, she found. Buildings and other infrastructure absorb sensible heat during the day and reradiate it throughout the night, but the cooling effect of evaporation is absent in cities. The lack of relief, particularly among the elderly population, can be deadly, she explained.

Ramped up air conditioning usage may have even exacerbated the problem, other data presented at the meeting suggests. Cecile de Munck, of the French Centre for Meteorological Research of Meteo-France, conducted a series of modeling experiments that show excess heat expelled onto the streets because of increased air conditioner usage during heat waves can elevate outside street temperatures significantly.

“The finding raises the question: what can we do to design our cities in ways that will blunt the worst effects of heat islands?” said de Munck, who notes also that her research shows that some types of air conditioning exacerbate heat islands more than others.

Making sure cities have trees and parks interspersed throughout the compact urban cores can also help defend against heat islands. And studies shows that painting the surfaces of roads and buildings white instead of black and creating “green” roofs that include vegetation can soften urban heat islands.

“There’s no one solution, and it’s going to be different for every city,” said Dousset. “Heat islands are complex phenomena.”

Related Links:

Beating the Heat in the World’s Big Cities

http://earthobservatory.nasa.gov/Features/GreenRoof/

EPA Heat Island Resources

www.epa.gov/heatisld

Ecosystem, Vegetation Affect Intensity of Urban Heat Island Effect

www.nasa.gov/mission_pages/terra/news/heat-islands.html

Urban Heat Island: Baltimore

http://earthobservatory.nasa.gov/IOTD/view.php?id=36227

Scientific Visualization Studio: Related Materials

http://svs.gsfc.nasa.gov/vis/a010000/a010600/a010699/index.html

Briefing Materials: Slideshows

Lead Author Ping Zhang; Goddard Space Flight Center

› Download pdf

Benedicte Dousset, University of Hawaii

› Download pdf

Cecile de Munck; French Centre for Meteorological Research of Meteo-France

› Download pdf Adam Voiland

NASA’s Earth Science News Team

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JEM

I think we have a new cause.
Stop Urban Warming.
Roll The Bulldozers Now!

Paddy

As I recall the assumption/adjustment for UHI in most GCMs is +0.5C. If I am correct, why hasn’t Hansen been shackled and perp-walked into a paddy wagon for a journey to the slammer?

Wyguy

Wow! Detroit may be on to something, bulldozing buildings the make open land!
Who knew!

latitude

“However, accurate comparisons have long eluded scientists because ground-based air temperature sensors tend to be unevenly distributed and prone to local bias. The lack of quantifiable definitions for urban versus non-urban areas has also hindered comparisons.”
=====================================================
It’s only 1/2 a degree….
…..I thought they knew what they were doing
😉

David

Now, I thought that when us ‘skeptics’ have raised the issue of urban heat islands in the past as having a significant effect on perceived ‘warming’, we were told sniffily by the warmists that the effect was ‘negligible’.
Surely we’re not being shown to have been right all along…!

jorgekafkazar

“…The U.S. Environmental Protection Agency estimates that, between 1979 and 2003, heat exposure has caused more than the number of mortalities resulting from hurricanes, lightning, tornadoes, floods, and earthquakes combined…”
And what about ice, snow storms and cold weather?

Dave F

7 to 9C warmer. Hmm, that might be enough to screw with an average…
What happened to using night lights?

LearDog

It is gratifying to finally see some explicit acknowledgment of this – the magnitude of which is frankly, larger than I expected.
Now – to just find out how GISS ‘corrects’ for their official data in these areas ….
Intra-Goddard politics ought to be interesting right about now …. I did note that there was no earth lights at night image to compare to the surface heat image.

keith at hastings uk

Well, we’ve known about this but quantification must be good. To know growth of UHI over time would very useful I suppose, given all those thermometers in Urban areas/airports, used to calculate Global warming. Sorry, estimate Gw, I mean guess, I mean show what we knew was true all along….

latitude

David says:
December 14, 2010 at 10:33 am
we were told sniffily by the warmists that the effect was ‘negligible’.
================================================
“”The compact city of Providence, R.I., for example, has surface temperatures that are about 12.2 °C (21.9 °F) warmer than the surrounding countryside””
========================================================
Are they really saying 20F warmer!
If they are, that is a whole lot more than even I thought.

Alan S. Blue

This is excellent.
Now we “just” need to locate the surface stations on those plots and compare “actual UHI” to the current “adjustments”.

Common Sense

Heck, who needs a thermometer? Just drive by a gold course with the windows open, then drive by a large shopping area.
People have known about this effect for hundreds of years. That’s why the aristocracy in Europe had summer houses in the country. In the Denver area, Molly Brown had a summer house in what was then the country (now it’s a suburb). They knew that being surrounded by grass and trees was cooler than being surrounded by buildings and concrete.

Gary

Heat in Providence and other coastal cities may be greater than the surrounding forested areas because of the ocean influence. Summertime afternoons are dominated by sea breezes that will cool the countryside while the city is still absorbing sunlight.

crosspatch

“Heat islands can be deadly.”
Which is one reason I actually support such things as cool roofs and cool pavements. In places where the dominant climate control cost is cooling, such activities (according to a study by UCLA) can cut urban temperatures by up to 2 degrees F. That 2 degrees amounts to a lot of energy that doesn’t have to be spent cooling things down that additional 2 degrees. It turns into savings for everyone in the area.
Also, things like “cool roof” technologies also help in even Northern winter areas. They provide greater insulation resulting in less heat loss and the white coating reflects heat back into the building rather than allowing the roof to act as an efficient radiator of energy into space (when it isn’t covered with snow).
We have the technology at hand to reduce UHI by a degree or two in most places. Winter UHI is mostly due to heat loss, the same technologies that reflect heat away in summer also reflect heat back in during winter again resulting in lower energy costs.
We might have a flake for the head of our Dept. of Energy but when he called for people to paint their roofs white, he was dead on the right track.. Doing that simple thing would save a large amount of energy in the US.

RHS

21.9 °F? Holy phun, that’s got to be statistically significant at any level. To bad it isn’t helping the East Coast right now. Ok, so that’s the extreme observation. Even an average of 13°F to 16 °F has got make Al Gore want new numbers. Wait, never mind, the only numbers we’ll see from him are from his weight…
Can’t wait to see the results after they re-run their predictive models with new and “correct” information…

Varco

Its interesting that the lack of vegetation seems to be so important. Is that why there is such a non-linear response to population? As I recall the urban heating effect kicks in pretty quickly as an area first moves from rural to lightly populated and then saturates quickly as population increases – at least this was the understanding before this paper? As developers move in the first thing they do is remove the vegetation, long before back-filling with concrete and people etc?

etudiant

Wow!!
These are just massive numbers, over 10 degrees C.
I’ve never ever seen an UHI estimate of the magnitude given here.
The usual estimate is 2 or 3 degrees, at least afaik.
It has been my understanding that the AGW proponents dismissal of UHI effects is based on the perception that the UHI impact is pretty stable, so that the larger scale trend in temperature will be the same, just with a different base. If however the UHI effect is as large and as variable as is reported in this study, that assumption is clearly in error and the debate about the impact of UHI on AGW is going into extra innings. A 10+degree C UHI effect will drown any 1 degree per century AGW signal.

Jim G

latitude says: December 14, 2010 at 10:39 amDavid says:
December 14, 2010 at 10:33 am
we were told sniffily by the warmists that the effect was ‘negligible’.
================================================
“”The compact city of Providence, R.I., for example, has surface temperatures that are about 12.2 °C (21.9 °F) warmer than the surrounding countryside””
========================================================
“Are they really saying 20F warmer!
If they are, that is a whole lot more than even I thought.”
Don’t know the territory back there well enough to evaluate but here in WY the temp can easily vary that much with as little as 1000ft change of elevation in the winter with the cold settling into the lower areas, particularly along waterways. And that is without any real heat islands to contaminate the situation. Hunting many mornings this year before dawn it would be 5 to 10 F at 5000ft and 10 to 15 below 0 F at 4000ft. The entire notion of monitoring ground level temperatures is very unscientific since there are many, many variables involved in measurement locations that are not well taken into account. Heat islands are just one of them. Obviously, one can get what one wants by location selection.

Harry Doyle

Another group of NASA scientists will have to removed from Hansen’s christmas card list.

Chiefio (E.M. Smith) had an interesting post on his blog re night lights as proxy for urban heat islands.
http://chiefio.wordpress.com/2010/11/01/golden-juarez/

Katherine

So in order to reduce UHI, we should cut down the forests and convert them to farmland? /sarc
Re the deaths in the Paris heat, I seem to remember reading somewhere that a lot of that was because the older folk didn’t have air-conditioning and had no one to check up on them. I can’t believe they’re advocating shutting off air-conditioning when it’s one of the best advances in heat adaptation. Obviously, there’s no mention of cold mortality because that’s just not on message for CAGW.

Billy Ruff'n

Wonder why they didn’t also analyse the accuracy of night time pixel counts as the proxy for UHI in the cities they studied. But then, maybe they did and decided there was nothing to see there and moved on.
Also, it seems funny that there’s no warning that by 2050 UHI will combine with AGW to make the cities of the world uninhabitable in summer months.

mondo

Sorry to be pedantic, but we really should encourage precision in language here. It is vitally important to distinguish between observed UHI (as here) and what we might term Delta UHI – change in UHI over time – as population grows for example.
If there is no change to UHI over time (as might be the case in a city that has reached physical limits and is no longer growing) then UHI will in that case will NOT be making a contribution to observed warming, coz the temperature in that city will likely NOT be increasing. ie Delta UHI will be zero.
In contrast, where a city is growing rapidly, and formerly rural temperature stations are being overwhelmed by development, the Delta UHI will be substantial, and making a contribution to observed warming. Clearly that contribution should be excluded.
The performance of “The Team” in dealing with this issue (actually NOT dealing with it) is one of the main reasons that they have lost credibility.

Dave F

An interesting point. If the Global Mean Temperature can be hindcasted correctly by global climate models without accounting for interference by the Urban Heat Island effect, they are wrong.
If the GMT is skewed by UHI, then the GCMs are DOA, ok?
Another interesting tidbit here. Check out this quote:
“The compact city of Providence, R.I., for example, has surface temperatures that are about 12.2 °C (21.9 °F) warmer than the surrounding countryside, while similarly-sized but spread-out Buffalo, N.Y., produces a heat island of only about 7.2 °C (12.9 °F), according to satellite data.”
It’s only roughly an order of magnitude higher than the GISS anomaly. No biggie, right?

Jeff L

“ground-based air temperature sensors tend to be unevenly distributed and prone to local bias”
And why then do we trust the historic surface temperature record ????

Clyde

Are they, perhaps, setting it up to turn all of the exaggerated temperature trends on their head and take control of the world through a quest to combat global cooling? Certainly once they make the appropriate corrections to the data they’ve been gathering, we’ll be in a hocky-stick drop in temperatures which is “unprecidented in history” and must be man-made.

D Snyder

Err, Doesn’t this mean there’s thermal radiation escaping to space?

Paula Werme

Wait a minute – I lived in Buffalo. It rarely gets over 90 degrees in western NY because of the lake effect. Of course there was a notable exception the day my brother got married – almost 100 degrees in an church with no air conditioning! The reception was a lot better than the wedding!
At any rate, I hope you’re not attempting to compare the climate of Providence with Buffalo – no nearby Great Lake to cool it down. Ocean doesn’t count with most of the weather coming from the west or south.

Dan in Nevada

So when GISTEMP adjusts past temperatures downward by 13-16℉ to properly account for this …

Where will Phil Jones hide the following toilet paper:
http://www.informath.org/apprise/a5620/b90.pdf
Ecotretas

juanslayton

The U.S. Environmental Protection Agency estimates that, between 1979 and 2003, heat exposure has caused more than the number of mortalities
resulting from hurricanes, lightning, tornadoes, floods, and earthquakes combined.

This statement appears to be a non-quantified update from:
http://www.epa.gov/aging/resources/epareportst.htm :
From 1979 -1999, excessive heat exposure caused 8,015 deaths in the United States. During this period, more people in this country died from
extreme heat than from hurricanes, lightning, tornadoes, floods, and earthquakes combined.

My question: Does this figure include the considerable number of heat related deaths on our southern boarder?
http://www.gao.gov/new.items/d06770.pdf :
From the late 1980s through the early 1990s, the
number of border-crossing deaths declined. Then, from the late 1990s
through 2005, the number of deaths approximately doubled. For example,
our analysis of the BSI data shows that the annual number of border-
crossing deaths increased from 241 in 1999 to a total of 472 deaths
recorded in 2005. Further, the majority of the increase in deaths during
this period occurred within the Border Patrol’s Tucson Sector—which
includes much of the Arizona desert. Our analysis of the NCHS data
indicates that, between 1990 and 2003, more than three-fourths of the rise
in migrant border-crossing deaths along the southwest border can be
attributed to an increase in deaths in the Tucson Sector. Over this period,
deaths due to exposure, especially heat-related exposure, increased
substantially…

Changes in the incidence of heat-related deaths may have more to do with changes in border enforcement than with climate.

Phil

@mondo says:
December 14, 2010 at 11:21 am
The amount of warming according to the theory formerly known as AGW over the past century or so is about 0.7 degrees C, IIRC. I doubt there are any cities on Earth that have not had a significant delta UHI over that period. For example, I knew someone who was born on a dairy farm in Brooklyn. How many farms, let alone dairy farms are there in Brooklyn today?
Furthermore, there has been a great shift in population from rural to urban worldwide. Now I believe more than half of the world’s population lives in cities, whereas a century or so ago most of the world’s population was rural.
In addition, if you expand your scale to that of the “hokey stick” (sic), I think a decent argument can be made in most cases that today’s observed UHI is roughly equal to delta UHI over say a thousand years. There is also a paper by Pielke that has a very strong correlation between warming and development, but I need to look that up.
It may well be that there is anthropogenic warming, but that such anthropogenic warming may be due to development, land use, etc. and not necessarily CO2. So spending countless trillions on reducing CO2 may not provide any measurable improvement. Painting roofs white is a great idea. Comparatively speaking (to CO2 reduction), it isn’t that expensive and it does not have any real drawbacks.

noaaprogrammer

Common Sense wrote:
“… That’s why the aristocracy in Europe had summer houses in the country…They knew that being surrounded by grass and trees was cooler than being surrounded by buildings and concrete.”
-not only cities but houses themselves were heat islands before the days of air conditioning. On the farm, my great grandparents had a summer kitchen (a separate building from the house) where the women could cook and bake and the family could eat during the summer without sweating too much. This also kept the bedrooms in the house cooler for better sleeping. (In very large families with many hired farm hands, cooking from scratch meant that preparation for the next meal of the day started after cleaning up from the previous meal, so the wood stoves were going all day long.)

AJB

All the hyperventilating over stupid windmills and here we see energy being poured into the atmosphere wholesale. What a ridiculous waste. There’s a fortune to be made here in cheap, effective waste heat recovery.

Bernie

Mondo:
What you say is true – it is the delta that is important. However, this research which suggests a very large UHI effect suggests that the actual delta could indeed be significant, i.e., size matters. The interesting data would be the size of the UHI in Siberia and China as development takes place and the UHI of relative small locations close to the Arctic Circle.
The other issue is that spreading temperatures based on a simple algorithm a la GISS and CRU/Jones may lead to many funny results.

harrywr2

mondo says:
December 14, 2010 at 11:21 am
“Sorry to be pedantic, but we really should encourage precision in language here. It is vitally important to distinguish between observed UHI (as here) and what we might term Delta UHI – change in UHI over time – as population grows for example.”
The UHI appears to be a function of impervious surface and surrounding vegetation.
If there is a single industry that has grown exponentially it is air travel. The amount of impervious surface at the airport has grown almost everywhere since the introduction of the Boeing 747. The thermometers are mostly at the airport. Airport runways have gotten longer and wider, the parking areas have gotten so large at some airports you need to take a bus to the actual airport. Grass strips have become gravel runways have become paved etc etc etc.

TerryS

Re: mondo

If there is no change to UHI over time (as might be the case in a city that has reached physical limits and is no longer growing) then UHI will in that case will NOT be making a contribution to observed warming, coz the temperature in that city will likely NOT be increasing. ie Delta UHI will be zero.

Yes that is true. However, at some point in the past Providence (for example) will have gone from 0c difference with the surrounding countryside to a 12.2c difference and this will be represented by an upward trend in the delta. If it took 100 years to go from 0c to 12.2c then the trend for that period has to be decreased by 12.2c/century.

Dr A Burns

The big question is exactly how much of the warming in the past century is UHI ?
If the IPCC included UHI instead of claiming it was negligible, wouldn’t the temperature graph look very different ?

Robuk

Why are urban weather stations used for the temperature sets when there adequate prestine rural stations dating back to 1900, in fact you only have to go back to the 1940`s to understand how UHI has effected these data sets.
Urban and rural stations are compared so that the UHI effect can be removed from the urban signal, why not just use the prestine rural temps, is there a problem with this.
Why has there been no peer reviewed study comparing rural with urban.
This is not science it`s trickery.

Sore_ron

Anybody plotted the position of the weather stations against these data ?

This is certainly a larger than expected result, 10+ °C is very significant. Maybe only 0.5 °C of the total global warming has been the UHI. Oh, 0.5 °C is the entire warming that has happened in the past 70 years.
One more reason to ignore station data. The UAH still shows warming in the Arctic and cooling in the Antarctic. So something is going on, but surprisingly enough it isn’t what warmists would like us to think.
John Kehr

Jeff (of Colorado)

Mondo says “If there is no change to UHI over time (as might be the case in a city that has reached physical limits and is no longer growing) then UHI will in that case will NOT be making a contribution to observed warming, coz the temperature in that city will likely NOT be increasing. ie Delta UHI will be zero.”
True, but would be hard pressed to find a major city (except Venice) that has stayed the same size over the last 100 years. Since cities have grown over the last 100 years, then their UHI has grown and that must be subtracted from recorded temperatures to get accurate changes. If these kind of temperatures as reported are correct, then as rural station records have shown all along, there is no significant global warming.
My initial skepticism looks at the comment about Las Vegas (as having little UHI), contrasted to the Las Vegas UHI report on WUWT showing a large change, and having some doubts to accuracy. True, the WUWT report was one day with one sensor.

Russ R.

My personal view (and I could be convinced otherwise) is that the impact of UHI effects on estimates of CHANGES in global average surface temperature can only be significant on time periods of at least a few decades. Cities tend to take a long time to develop and grow.
Yes, all the data show that any city is warmer than the surrounding countryside, often by a substantial amount, but how much has that temperature difference changed from last year? 10 years ago? 20 years ago? 50 years ago?
The easiest way to look at the impact on global average temperatures is to compare estimates based on surface measurements (which are affected by UHI, and subsequently adjustmented to neutralize the impact) against those based on satellite measurements (which should be completely immune from UHI effects).
A quick comparison of HADCRUT3 vs. UAH from 1979 to present (Oct 2010) shows hardly any difference in trend (+0.158 vs. +0.140 deg C/decade): http://woodfortrees.org/plot/hadcrut3vgl/from:1979/to:2010.75/plot/uah/from:1979/to:2010.75/plot/hadcrut3vgl/from:1979/to:2010.75/trend/plot/uah/from:1979/to:2010.75/trend
So, when the difference between the two estimates is only +0.018 deg C / decade, I can only conclude that either (1) UHI is adequately corrected for, or (2) if the adjustments to correct for UHI are somehow inaccurate, the net impact is close to trivial.

Kev-in-UK

mondo says:
December 14, 2010 at 11:21 am
thats very true – but here in the Uk, there are other issues – such as when central heating was installed and coal fires (where most of the heat escaped out the chminey) stopped being used. Then you have the issue of motor vehicles – as in the actual number of vehicles on the road in a city, and the length of time they are on the road due to increased traffic.
IMO – any records from towns and cities should be given a very wide berth because back analysis will not be able to accurately define warming due to UHI. Has anyone performed a check of GMT trends from ONLY rural stations?

Anonymous Howard

Glad to see those corrupt researchers at NASA’s Goddard Institute for Space Studies are finally being shown the truth by… researchers at NASA’s Goddard Space Flight Center.

Pops
GregS

“”The compact city of Providence, R.I., for example, has surface temperatures that are about 12.2 °C (21.9 °F) warmer than the surrounding countryside””
Careful here. They are talking about temperature on the surface, not the temperature a few feet above the surface. Even in mid-winter Minneapolis when the official temperature is -10F, it is not at all unusual to record streets and parking lot surface temperatures of 40F. That is how why you see dry pavement in mid-winter Minnesota.
But surface temperature is not UHI, though the two are connected.
So….. it may be -10F in Minneapolis, the asphalt in your parking lot may be 40F, and -12F in the distant burbs. The 2F difference is UHI, the 50F diff in the parking lot is merely micro-climate.
I suppose that is clear as mud, but it is the best I can do. (sigh)

UK John

I have always thought that there os some evidence that the smokey/foggy cities of 100 years ago were actually cooler in the winter, if compared to comparable sized cities today, due to the fog and smog.
So in the winter the UHI effect over time has actually gone from sort of negative to extremely positive.
In summer all the heat expelled from air conditioning systems makes modern cities much hotter when compared to comparable sized cities of 100 years ago.

Jimash

Now we know why the urban glaciers are melting.
Seriously though, doesn’t this finding demand a reparametrization,
and re-run of the Monte Carlo Roulette wheel Global Climate Models ?
That is going to leave a mark, methinks a distinctly downward facing mark.
IF the tables turn and a new regime is discerned, will we still have to rely on the same group of numbskulls and frauds to study it ?

Yarmy

What matters is not how much warmer a weather station located in the City is than a weather station located outside but how much warmer that City station has become over time. It’s been suggested that measuring the changing population density would be a useful way to calculate that and this study seems to confirm it.