Urban 'heat island' effect is only a small contributor to global warming, and white roofs don't help

[OKIsItJustMe]

http://news.stanford.edu/news/2011/october/urban-heat-islands-101911.html

Stanford Report, October 19, 2011

Urban 'heat island' effect is only a small contributor to global warming, and white roofs don't help to solve the problem, say Stanford researchers

Heat emanating from cities – called the "urban heat island" effect – is not a significant contributor to global warming, Stanford researchers have found. They also concluded that if all the roofs in urban areas were painted white, it would increase, not decrease, global warming.

BY LOUIS BERGERON

Cities release more heat to the atmosphere than the rural vegetated areas around them, but how much influence these urban "heat islands" have on global warming has been a matter of debate. Now a study by Stanford researchers has quantified the contribution of the heat islands for the first time, showing that it is modest compared with what greenhouse gases contribute to 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 Z. Jacobson, a professor of civil and environmental engineering who led the study. He and graduate student John Ten Hoeve compare this with the greenhouse gas contribution to gross warming of about 79 percent and the black carbon contribution of about 18 percent.

…

Jacobson and Ten Hoeve are authors of a paper describing the research that will be published in Journal of Climate. The paper is available online http://www.stanford.edu/group/efmh/jacobson/Articles/Others/HeatIsland+WhiteRfs0911.pdf">now. The study modeled climate response from 2005 to 2025.

…

[kestrel91316]

1. White roofs won't decrease global warming? O RLY??

Funny, I thought the purpose of them was to decrease AC bills for occupants and theoretically decrease energy usage.

Not sure anybody complained that they would do anything other than that. Nor that the heat island effect was anything more than a SYMPTOM of the problem.

[Viking12]

2. You've pointed out the limitation of this paper's results...

As the paper expresses....

"A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ~0.02 K but to
warm the Earth overall by ~0.07 K. White-roof local cooling may also affect energy use, thus emissions, a factor not accounted for here."

[marybourg]

3. Yes. Here in AZ they've been touted as a remedy for our

urban heat island effect.

[OKIsItJustMe]

5. Painting roofs white has been suggested as a method of geoengineering by increasing global albedo

See, for example:

http://www2.ucar.edu/news/1385/computer-model-demonstrates-white-roofs-may-successfully-cool-cities

Computer model demonstrates that white roofs may successfully cool cities

January 28, 2010

BOULDER—Painting the roofs of buildings white has the potential to significantly cool cities and mitigate some impacts of global warming, a new study indicates. The new NCAR-led research suggests there may be merit to an idea advanced by U.S. Energy Secretary Steven Chu that white roofs can be an important tool to help society adjust to climate change.

But the study team, led by scientists at the National Center for Atmospheric Research (NCAR), cautions that there are still many hurdles between the concept and actual use of white roofs to counteract rising temperatures.

"Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat," says NCAR scientist Keith Oleson, the lead author of the study. "It remains to be seen if it's actually feasible for cities to paint their roofs white, but the idea certainly warrants further investigation."

The study is slated for publication later this winter in Geophysical Research Letters. It was funded by the National Science Foundation, NCAR's sponsor.

…

http://dx.doi.org/10.1029/2009GL042194


http://thinkprogress.org/romm/2009/01/06/203098/geo-engineering-adaptation-mitigation-green-stimulus-white-roofs-albedo/

Geoengineering, adaptation and mitigation, Part 2: White roofs are the trillion-dollar solution

By Joe Romm on Jan 6, 2009 at 12:16 pm

Part I introduced urban heat island mitigation (UHIM). It discussed how lighter colored (or reflective) roofs and pavement, plus urban trees, can save energy, cut CO2 emissions, cool a city, and reduce smog.

But a global “cool roofs” strategy can achieve far bigger benefits — the equivalent of several trillion dollars worth of CO2 reductions — since it can increase the albedo (reflectivity) of the planet, thereby directly reducing the absorption of incoming solar radiation and hence planetary warming. The strategy proposed below “is equivalent to taking the world’s approximately 600 million cars off the road for 18 years.”

…

http://dx.doi.org/10.1007/s10584-008-9515-9

Global cooling: increasing world-wide urban albedos to offset CO2

Hashem Akbari, Surabi Menon and Arthur Rosenfeld

Abstract

Increasing urban albedo can reduce summertime temperatures, resulting in better air quality and savings from reduced air-conditioning costs. In addition, increasing urban albedo can result in less absorption of incoming solar radiation by the surface-troposphere system, countering to some extent the global scale effects of increasing greenhouse gas concentrations. Pavements and roofs typically constitute over 60% of urban surfaces (roof 20–25%, pavements about 40%). Using reflective materials, both roof and pavement albedos can be increased by about 0.25 and 0.15, respectively, resulting in a net albedo increase for urban areas of about 0.1. On a global basis, we estimate that increasing the world-wide albedos of urban roofs and paved surfaces will induce a negative radiative forcing on the earth equivalent to offsetting about 44 Gt of CO2 emissions. At ∼$25/tonne of CO2, a 44 Gt CO2 emission offset from changing the albedo of roofs and paved surfaces is worth about $1,100 billion. Furthermore, many studies have demonstrated reductions of more than 20% in cooling costs for buildings whose rooftop albedo has been increased from 10–20% to about 60% (in the US, potential savings exceed $1 billion per year). Our estimated CO2 offsets from albedo modifications are dependent on assumptions used in this study, but nevertheless demonstrate remarkable global cooling potentials that may be obtained from cooler roofs and pavements.

…

[Viking12]

7. neither of the articles suggest the albedo increase from white roofs would have global significance

No global geoengineering implied. Both are quite focused on the local, urban warming relief created by increased albedo (although the second does suggest broader effects due to reduced carbon emissions from cooling savings). Although the UHI effect does not play a significant role in global temps, it makes a big difference to the local inhabitants, especially the influence on air quality.

Understanding the nuance of scientific articles is important.

[OKIsItJustMe]

8. Seriously? They don’t? Would you like something a little more explicit?

http://www.energy.ca.gov/2008publications/CEC-999-2008-031/CEC-999-2008-031.PDF

Research Highlights LBNL Heat Island Group November 10, 2008

White Roofs Cool the World,
Directly Offset CO₂ and Delay Global Warming

As the threat of global warming becomes widely recognized, scientists have proposed using geo-engineering (manipulation of the Earth’s environment) to quickly respond to this threat. Most proposed geo-engineering techniques are novel and unproven. Two simple technologies that have been around for thousands of years, cool roofs and cool pavements, should be the first geo-engineering techniques used to combat global warming.

Increasing the solar reflectance of urban surfaces reduces their solar heat gain, lowers their temperatures, and avoids transferring heat back into the atmosphere. This process of “negative radiative forcing” counters global warming. In a recent study to be published in journal Climatic Change, Akbari, Menon and Rosenfeld have calculated the CO₂ offset, or equivalent reduction in CO₂ emission, achieved by increasing the solar reflectance of urban surfacesCO¹.

…

If only roofs are changed from their current dark colors to white for flat roofs and cool colors for sloped roofs, we can offset 24 billion tonnes of CO₂. If we take 20 years to implement just the cool roofs portion, it’s the equivalent of taking half of the cars in the world off the road for every year of the 20 year program (see table). The offset provided by cooling urban surfaces affords us a significant delay in climate change during which we can take further measures to improve energy efficiency and sustainability.

Akbari et al. propose an international campaign to use solar reflective materials when roofs and pavements are initially built or resurfaced in temperate and tropical regions. They point out that such an international “cool cities” program is a win, win, win proposition. Cool roofs reduce cooling-energy use in air conditioned buildings and increase comfort in unconditioned buildings (win #1). Cool roofs and cool pavements mitigate summer urban heat islands, improving outdoor air quality and comfort (win #2). This latest research shows that cool roofs and cool pavements can cool the entire globe (win #3). Installing cool roofs and cool pavements in cities worldwide does not require delicate international negotiations about capping CO₂ emission rates.

…

[Viking12]

9. Did you read the article?

Conclusion:
"Converting to cool urban surfaces does not address the underlying problem of global warming, which results from the emissions of greenhouse gases and absorbing particles. The problem of global warming emissions must be resolved by developing and implementing a complete portfolio of measures to reduce GHG emissions. We also note that the cool urban surfaces, particularly cool roofs, yield significant energy savings and hence a reduction in GHG emissions. The global cooling effect of increasing urban solar reflectance is an added effect that is quantified here." (p. 9)

[OKIsItJustMe]

12. Did you read it?

The paragraph you cite simply says that that the problem of Greenhouse gases will still need to be addressed.

The paper itself is quite clear that they’re talking about global effects through albedo changes: (emphasis added by me)

Global Cooling: Increasing World-wide Urban Albedos to Offset CO₂

Hashem Akbari and Surabi Menon
Lawrence Berkeley National Laboratory, USA

Arthur Rosenfeld
California Energy Commission, USA

January 14, 2008

ABSTRACT

Modification of urban albedos reduces summertime urban temperatures, resulting in a better urban air quality and building air-conditioning savings. Furthermore, increasing urban albedos has the added benefit of reflecting some of the incoming global solar radiation and countering to some extent the effects of global warming. In many urban areas, pavements and roofs constitute over 60% of urban surfaces (roof 20-25%, pavements about 40%). Using reflective materials, both roof and the pavement albedos can be increased by about 0.25 and 0.10, respectively, resulting in a net albedo increase for urban areas of about 0.1. Many studies have demonstrated building cooling-energy savings in excess of 20% upon raising roof reflectivity from an existing 10-20% to about 60% (a U.S. potential savings in excess of $1 billion (B) per year in net annual energy bills).

On a global basis, our preliminary estimate is that increasing the world-wide albedos of urban roofs and paved surfaces will induce a negative radiative forcing on the earth equivalent to removing ~22 - 40 Gt of CO₂ from the atmosphere. Since, 55% of the emitted CO₂ remains in the atmosphere, removal of 22 - 40 Gt of CO₂ from the atmosphere is equivalent to reducing global CO₂ emissions by 40 - 73 Gt. At ~$25/tonne of CO₂, a 40 - 73 Gt CO₂ emission reduction from changing the albedo of roofs and paved surfaces is worth about $1,000B to 1800B. These estimated savings are dependent on assumptions used in this study, but nevertheless demonstrate considerable benefits that may be obtained from cooler roofs and pavements.

1 INTRODUCTION

In many urban areas, pavements and roofs constitute over 60% of urban surfaces (see Table 1; roof 20-25%, pavements about 40%) (Akbari et al., 2003, Rose et al., 2003, Akbari and Rose 2001a, Akbari and Rose 2001b). Many studies have demonstrated building cooling-energy savings in excess of 20% upon raising roof reflectivity from an existing 10-20% to about 60%. We estimate a U.S. potential savings in excess of $1 billion (B) per year in net annual energy bills (cooling-energy savings minus heating-energy penalties). Increasing the albedo of urban surfaces (roofs and pavements) can reduce the summertime urban temperature and improve the urban air quality (Taha 2002; Taha 2001; Taha et al. 2000; Rosenfeld et al. 1998; Akbari et al. 2001, Pomerantz et al. 1999). The energy and air quality savings resulting from increasing urban surface abedos in the U.S. alone can exceed $2B per year.

Increasing the urban albedo has the added benefit of reflecting more of the incoming global solar radiation and countering to some extent the effects of global warming (Kaarsberg and Akbari, 2006). Here we quantify the effect of increasing the albedo of urban areas on global warming.

…

[kristopher]

13. Jacobson and Ten Hoeve are showing a problem with Akbari's approach

One geoengineering proposal to ameliorate the effects of the UHI contribution to global warming has been to use reflective roofing material or to paint existing roofs white. White roofs have generally been thought to reduce summer air conditioning energy demand and change the albedo of the surface. In such cases, the impact of converting roofs to white coatings should be to cool roofs initially . Akbari et al. <2009> estimated the surface albedo change from using reflective coatings on all roofs and pavements worldwide. That study used scaling arguments to estimate the equivalent carbon dioxide savings due to cooler global temperatures following such a conversion. However, they did not use a global model to simulate whether the conversion caused a net cooling or warming of global climate.

Menon et al. <2010> went further by using a land-surface model to calculate the change in surface temperature due to changing all urban albedos worldwide by 0.1 and estimated a cooling. However, they did not calculate the climate response with an atmospheric model. As a result, they did not account for the effects of the albedo change on atmospheric stability, clouds, or the feedbacks to large-scale meteorology or climate. Oleson et al. <2010> expanded on these studies by treating white roofs in a global climate model as subgrid phenomena, also accounting for changes in air conditioning and space heating demand. Although their model included feedbacks to the larger scale, they reported temperature differences only between urban areas and nearby rural areas, so they did not determine the globally-averaged temperature change due to white roofs. While they found a net cooling in urban areas due to white roofs as with the previous studies, they also found that white roofs increased space heating in the annual average more than they decreased air conditioning use (which occurs mostly in the summer).

[OKIsItJustMe]

15. The OP also shows that painting roofs white won’t help cool the planet

The question seems to be over whether anyone ever claimed that it would or not.

[kristopher]

16. The Jacobson & Ten Hoeve paper IS the study in the OP

Also, your post #14 makes an explicit point to note that preliminary work indicates that the global significance might be limited to only a delay in the warming trend. In sum either of your opinions could be supported. It's too bad so much discussion wasn't devoted to integrating the *important* meaning of the entire body of work for those who have less experience understanding how to interpret ongoing research.

[Viking12]

20. ...or, more precisely, whether the scientific articles actually claimed that it would.

You've largely built your position on press releases and popular publications and not the actual findings of the studies. While it appears from press releases that the article referenced in the OP is contrary to the other articles (again, based on press releases), they are in fact quite consistent in their findings. In short, UHI is negligible in the big picture. Thus, albedo changes that may reduce UHI are negligible in the big picture. That doesn't lead to the conclusion that white roofs are useless. To the contrary, they can influence local temps increasing air quality and reducing energy used for cooling. This latter aspect is ignored in the OP -- that doesn't make it a bad study, only that the study has limited utility and that's what my first point was. I'm not sure hoqw it got to here but that's DU....

As I mentioned above recognizing the nuance in scientific article is important.

[kristopher]

21. 1/2 of 1% of Earth's non-ice surface is covered with urban surfaces

Based on their method of resolving the details, "0.128% of the total Earth or 0.504% of the world’s non- permanent ice-covered land (which represents 25.4% of the Earth) was covered with urban surfaces in 2005 " which equated to 656,040 km2.

A comparison to previous data indicates that in the 13 years preceeding 2005 the urban surface area might have increased 249%.

They also note that their results with the more refined resolution showed that the urban surface area is only about 1/5th what was found in a 2010 study that used more coarse modeling based on city lighting.

More than half the urban area 52.2% was vegetated soil. "1.57% was estimated to be bare soil, 27.8% was estimated to be rooftops, and 18.5% was estimated to be impervious surfaces. As such, 46.3% of urban pixels consisted of rooftops plus impervious surface material."

They estimate global roof area as 181,900km2 and road areas at 121,300 km2.

"These areas compare with 380,000 km2 and 530,000 km2 assumed in Akbari et al. <2009> without the benefit of satellite analysis. They estimated that urban surface areas comprised 1% of all land (or 0.29% of the total Earth), which is about 2.26 times greater than that estimated by the satellite analysis here. They also assumed a roof to road ratio of 0.71:1 versus 1.5:1 estimated here. Walls were ignored here for radiative calculations since radiative transfer and subsurface heat/moisture fluxes were calculated in columns."

There is a treasure trove of information in this paper...

Thanks for the OP OK...
Download link
http://www.stanford.edu/group/efmh/jacobson/Articles/Others/HeatIsland+WhiteRfs0911.pdf

[OKIsItJustMe]

25. Well, no, that would be less precisely

Here’s the original question:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=314310&mesg_id=314317

1. White roofs won't decrease global warming? O RLY??

Funny, I thought the purpose of them was to decrease AC bills for occupants and theoretically decrease energy usage.

Not sure anybody complained that they would do anything other than that. Nor that the heat island effect was anything more than a SYMPTOM of the problem.

To which, I replied:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=314310&mesg_id=314331

5. Painting roofs white has been suggested as a method of geoengineering by increasing global albedo

See, for example:

…

http://dx.doi.org/10.1029/2009GL042194

…

http://dx.doi.org/10.1007/s10584-008-9515-9

…

These citations were to papers in scientific publications. (I also cited press releases about the papers, since I have found that many people prefer to read what amounts to a digest of the actual papers. It’s become my general practice to post an extract of a press release, and URL’s for the press release and the actual paper.)

Personally, I’m no skeptic regarding the “greenhouse effect,” “global warming,” “anthropogenic climate change,” (or whatever we may call it tomorrow) but I never thought that painting roofs white would have as significant effect on the Earth’s albedo as Akbari and company thought that it would, and Akbari’s work has been cited everywhere: http://www.google.com/search?q=Hashem+Akbari+white+roofs

I’ve gotten tired of reading about it again and again.


Do I just not appreciate nuance? Is that it?

Even the idea that white roofs save energy (due to less air conditioning) is bogus. It might be true for the South where air conditioning is heavily used, but it isn’t for the North, where we make more use of furnaces.


http://dx.doi.org/10.1029/2009GL042194

GEOPHYSICAL RESEARCH LETTERS, VOL. 37, L03701, doi:10.1029/2009GL042194, 2010

Effects of white roofs on urban temperature in a global climate model

K. W. Oleson and G. B. Bonan
Climate and Global Dynamics Division, National Center for Atmospheric Research,
Boulder, Colorado, USA

J. Feddema
Department of Geography, University of Kansas,
Lawrence, Kansas, USA

Abstract

|1| Increasing the albedo of urban surfaces has received attention as a strategy to mitigate urban heat islands. Here, the effects of globally installing white roofs are assessed using an urban canyon model coupled to a global climate model. Averaged over all urban areas, the annual mean heat island decreased by 33%. Urban daily maximum temperature decreased by 0.6°C and daily minimum temperature by 0.3°C. Spatial variability in the heat island response is caused by changes in absorbed solar radiation and specification of roof thermal admittance. At high latitudes in winter, the increase in roof albedo is less effective at reducing the heat island due to low incoming solar radiation, the high albedo of snow intercepted by roofs, and an increase in space heating that compensates for reduced solar heating. Global space heating increased more than air conditioning decreased, suggesting that end-use energy costs must be considered in evaluating the benefits of white roofs.

1. Introduction

|2| An analysis by Akbari et al. |2009| indicated that increasing the albedo of urban roofs and pavements globally could produce a negative radiative forcing equivalent to a 44 Gt CO₂ emission offset. This is equivalent to offsetting the effect of the growth in CO₂-equivalent emission rates for the next 11 years. It was also noted that potential energy savings may be realized due to a reduction in the amount of energy consumed by air conditioning to cool buildings. The effects of increasing the albedo of cities on near-surface climate, in particular air temperature, were not addressed.

…

3. Conclusions

|19| These results suggest that increasing the albedo of roofs is an effective way of reducing the urban heat island. The degree to which the heat island decreases depends on the importance of roofs relative to the rest of the urban system (i.e., building walls and canyon floor) in generating the heat island. This approach to heat island mitigation is less effective in winter at higher latitudes. At these latitudes, any benefits gained from a reduction in the summertime heat island need to be considered in the context of increased heating costs in winter. Increasing the albedo of roofs is also less effective for thin roofs constructed with high thermal admittance materials because these roofs have low storage capacities. Globally, white roofs cause a net increase in HAC fluxes due to a larger increase in space heating than decrease in air conditioning flux. As air conditioning more thoroughly penetrates the global market, however, white roofs might be expected to play a larger role in reducing this flux.

…

[Viking12]

26. Now where I have heard this before?

These results suggest that increasing the albedo of roofs is an effective way of reducing the urban heat island.

Either you don't read what you post or you have serious reading comprehension deficiencies.

Never said you were a skeptic, a denier. I only said you were wrong concerning the conclusions of the paper. I showed you in the very clear language of the paper's conclusion that the paper does not make the claims you and others may ascribe to it.

[OKIsItJustMe]

29. Others, like Akbari you mean

http://articles.latimes.com/2008/sep/10/local/me-roofs10

New anti-warming tool: white roofs

A major cooling effect could result from such structures and from reflective pavement, data show.

September 10, 2008|Margot Roosevelt | Times Staff Writer

…

According to Hashem Akbari, a physicist with the Lawrence Berkeley National Laboratory, a 1,000-square-foot roof -- the average size on an American home -- offsets 10 metric tons of planet-heating carbon dioxide emissions in the atmosphere if dark-colored shingles or coatings are replaced with white material.

…

Akbari's paper, "Global Cooling: Increasing Worldwide Urban Albedos to Offset CO2," to be published in the journal Climatic Change, was written with his colleague Surabi Menon and UC Berkeley physicist Arthur Rosenfeld, a member of the California Energy Commission. All three have been associated with the laboratory's Heat Island Group, which has published extensive research on how roofs and pavement raise urban temperatures.

Akbari and Rosenfeld said they will mount an effort to persuade the United Nations to organize major cities to alter their roofing and pavement.

"I call it win-win-win," Akbari said. "First, a cooler environment not only saves energy but improves comfort. Second, cooling a city by a few degrees dramatically reduces smog. And the third win is offsetting global warming."

http://www.azcoolroof.com/downloads/Resources/To%20Go%20Green,%20Roofs%20Should%20Go%20Green.pdf

Hashem Akbari's cool anti-global-warming plan

Justin Berton, Chronicle Staff Writer Friday, February 20, 2009

If Hashem Akbari's plan to stave off global warming is realized, it will come one rooftop at a time.

Akbari, a senior scientist at the Lawrence Berkeley National Laboratory, and a group of fellow geoengineers who are trying to counter the effects of climate change, have developed a relatively simple idea to offset carbon emissions and cool the Earth's urban surfaces: Make all rooftops and paved surfaces white.

Or at the very least, convert them to cool gray colors to reflect the sun's rays, instead of attracting and absorbing heat.

"We won't be solving the problem of global warming, by any means," Akbari said, "but we will be buying ourselves a little bit of breathing time."

…

[OKIsItJustMe]

14. Kaarsberg and Akbari, 2006 — COOL ROOFS COOL THE PLANET

http://heatisland.lbl.gov/content/cool-roofs-cool-planet

COOL ROOFS COOL THE PLANET

There’s an important, although little-known, advantage to cool roofs: They help cool the planet.

BY TINA KAARSBERG AND HASHEM AKBARI

The Summer 2006 heat wave resulted in dramatic increases in both A/C electric bills and homeowners’ interest in cool roofs. As Home Energy readers know, cool roofs can reduce A/C use by up to 20% and improve a home’s comfort in the event of a power loss (see “Cool Colored Roofs,” HE March/April ’06, p. 12). This article focuses on a lesser known cool roof benefit—their contribution to the Earth’s albedo or reflectivity. Approaches such as cool roofs that instantly reduce global warming may well turn out to be a critical tool in countering the risk of abrupt climate change.

…

The Global Benefits

Recently Hashem Akbari and Art Rosenfeld, of the California Energy Commission, estimated the global cooling impact of cool roofs in just the largest cities (1% of land) on Earth. These urban areas consist of about 25% roof and 35% paved surfaces. Based on their experience in California, Akbari and his collaborators assume that the albedo of roofs and pavements can be cost-effectively increased by 0.25 and 0.15 respectively for a net urban area albedo change of at least 0.1. They estimated the effect of such an albedo change on global warming, using simplified climate models, published global climate model (GCM) simulations, and their own simulations. While the local cooling due to modest cost-effective changes is dramatic (approximately -5°F), the global cooling is less impressive, averaging only 0.02°F, or a three-month delay in the warming due to current world emissions. Even this small global temperature change is equivalent to a reduction in emissions of 10 billion metric tons of CO₂, or a little more than one year of today’s U.S. carbon emissions.

Robert Hamway of the Centre for Economic and Ecological Studies in Geneva, Switzerland, recently conducted another estimate of the impact of raising earth’s surface albedo. His analysis differs from that described above in that he includes all human controlled surfaces, not just those in the largest cities, and he assumes a somewhat larger albedo increase in these areas (up to a = 0.3). His very preliminary estimates are derived using a static two-dimensional model without all the features of a full-blown GCM. He estimates a globally averaged change in radiative forcing of -0.17 W/m², or a delay of about six years in global warming. Note that the current total radiative imbalance of the Earth is approximately 0.9 W/m², so a decrease in forcing of this magnitude would decrease the net positive forcing by nearly 20%.

…

[kristopher]

4. The Abstract

Abstract.
Land use, vegetation, albedo, and soil-type data are combined in a global model that accounts for roofs and roads at near their actual resolution to quantify the effects of urban surface and white roofs on climate. In 2005, ~0.128% of the Earth’s surface contained urban landcover, half of which was vegetated. Urban landcover was modeled over 20 years to increase gross global warming (warming before cooling due to aerosols and albedo change are accounted for) by 0.06-0.11 K and population-weighted warming by 0.16-0.31 K, based on two simulations under different conditions. As such, the urban heat island (UHI) effect may contribute to 2-4% of gross global warming, although the uncertainty range is likely larger than the model range presented, and more verification is needed. This may be the first estimate of the UHI effect derived from a global model while considering both UHI local heating and large-scale feedbacks. Previous data estimates of the global UHI, which considered the effect of urban areas but did not treat feedbacks or isolate temperature change due to urban surfaces from other causes of urban temperature change, imply a smaller UHI effect but of similar order. White roofs change surface albedo and affect energy demand. A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ~0.02 K but to warm the Earth overall by ~0.07 K. White-roof local cooling may also affect energy use, thus emissions, a factor not accounted for here. As such, conclusions here regarding white roofs apply only to the assumptions made.

Broken apart:

Land use, vegetation, albedo, and soil-type data are combined in a global model that accounts for roofs and roads at near their actual resolution to quantify the effects of urban surface and white roofs on climate.

In 2005, ~0.128% of the Earth’s surface contained urban landcover, half of which was vegetated.

Urban landcover was modeled over 20 years to increase gross global warming (warming before cooling due to aerosols and albedo change are accounted for) by 0.06-0.11 K and population-weighted warming by 0.16-0.31 K, based on two simulations under different conditions.

As such, the urban heat island (UHI) effect may contribute to 2-4% of gross global warming, although the uncertainty range is likely larger than the model range presented, and more verification is needed.

This may be the first estimate of the UHI effect derived from a global model while considering both UHI local heating and large-scale feedbacks.

Previous data estimates of the global UHI, which considered the effect of urban areas but did not treat feedbacks or isolate temperature change due to urban surfaces from other causes of urban temperature change, imply a smaller UHI effect but of similar order.

White roofs change surface albedo and affect energy demand.

A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ~0.02 K but to warm the Earth overall by ~0.07 K.

White-roof local cooling may also affect energy use, thus emissions, a factor not accounted for here.

As such, conclusions here regarding white roofs apply only to the assumptions made. (Bold added)

[Fledermaus]

6. Its only a small effect when you don't live in a large city.

When you live in a large city its like living in an oven and increases power consumption to run AC.

[The Croquist]

10. Skeptics have been saying this for years

What they wonder is why so many surface stations are measured in areas with known urban heat island effects.

[Viking12]

11. Yawn

[The Croquist]

17. Brilliant rebuttal there Viking12

Maybe you can explain this to me. If white roofs would increase global warming wouldn't a lack of white ice in the Arctic reduce global warming? just wondering.

[kristopher]

18. Given the information in the thread above...

The fact that you would make such an obviously flawed connection in your mind is a valuable insight into the mental processes of of those who deny climate change.

Croquist:
"Maybe you can explain this to me. If white roofs would increase global warming wouldn't a lack of white ice in the Arctic reduce global warming? just wondering."

[The Croquist]

22. I guess that easier then explaining a contradiction

kristopher,
That was a pretty mild insult coming from you.

Let me try:
Not all albedos are created equal. Man made albedo bad. Natural albedo good.

PS: Anything done by man bad.

[kristopher]

23. It is clearly explained above.

And you can obviously read.

Therefore your post isn't about the facts of the matter, but something else.

What would that be?

[Viking12]

19. I could explain it to you but you wouldn't understand.

Just like you can't understand that thermometer location isn't influencing the global temperature record. It has been explained to death on this site yet you keep reviving the stupid idea, thus the zombie graphic.

[The Croquist]

24. Just like you can't understand that thermometer location isn't influencing the global temperature re

So putting thermometers next to A/C exhaust vents doesn't impact the temperature record?
Putting thermometers in asphalt parking lots doesn't impact the temperature record?
Putting thermometers in sewage plants doesn't impact the temperature record?
Putting thermometers next to airport runways doesn't impact the temperature record?
Putting thermometers on roof tops doesn't impact the temperature record?
Putting thermometers next microwave transmitters doesn't impact the temperature record?
Putting thermometers next to roads doesn't impact the temperature record?
Putting thermometers next to BBQ grills doesn't impact the temperature record?
Putting thermometers covered by vegetation doesn't impact the temperature record?
Putting thermometers next to buildings doesn't impact the temperature record?
Putting thermometers in a junkyard doesn't impact the temperature record?
Putting thermometers next to a Mig 15 doesn't impact the temperature record?
Putting thermometers in positions so that 93% fail minimum standards set by the Climate Reference Network doesn't impact the temperature record?

And people call me a denier...

[Viking12]

27. It's alive!

Is it the release of the Berkeley study that drives yet another nail in the coffin that's got you all riled up?

[OKIsItJustMe]

28. You may find this paper helpful

http://www.ncdc.noaa.gov/oa/wmo/ccl/rural-urban.pdf

Assessment of Urban Versus Rural In Situ Surface Temperatures in the Contiguous United States: No Difference Found

THOMAS C. PETERSON
National Climatic Data Center, Asheville, North Carolina
(Manuscript received 26 May 2002, in final form 23 February 2003)

ABSTRACT

All analyses of the impact of urban heat islands (UHIs) on in situ temperature observations suffer from inhomogeneities or biases in the data. These inhomogeneities make urban heat island analyses difficult and can lead to erroneous conclusions. To remove the biases caused by differences in elevation, latitude, time of observation, instrumentation, and nonstandard siting, a variety of adjustments were applied to the data. The resultant data were the most thoroughly homogenized and the homogeneity adjustments were the most rigorously evaluated and thoroughly documented of any large-scale UHI analysis to date. Using satellite night-lights–derived urban/ rural metadata, urban and rural temperatures from 289 stations in 40 clusters were compared using data from 1989 to 1991. Contrary to generally accepted wisdom, no statistically significant impact of urbanization could be found in annual temperatures. It is postulated that this is due to micro- and local-scale impacts dominating over the mesoscale urban heat island. Industrial sections of towns may well be significantly warmer than rural sites, but urban meteorological observations are more likely to be made within park cool islands than industrial regions.

…

Follow the link for the whole paper…

[GliderGuider]

30. Oh, snap!

Very nice. :-) Very nice indeed! :-)

:toast:

[Viking12]

31. or any of these...

http://www1.ncdc.noaa.gov/pub/data/ushcn/v2/monthly/menne-etal2010.pdf

ftp://ftp.ncdc.noaa.gov/pub/data/papers/200686ams3.10tpfree.pdf

http://pubs.giss.nasa.gov/docs/2001/2001_Hansen_etal.pdf

http://berkeleyearth.org/resources.php

The denier zombie has been given all of this information previously, yet still continues to resuscitate long dead arguments from anecdote.