Effects Of Urban Heat Island On Climate

[morfius]

With the human race altering ever increasing amounts of the Earth's surface, I have always wondered if the urban heat island effect could be affecting global temperatures.

Take London as an example - on satellite photos it never fails to amaze me how massive the urban area actually is. The fact that we can see London from space shows just how significant it is. Now take all the other major urban areas, roads, and other man made surfaces, and you can see the big picture. Surely all of this across the entire planet acts as a massive central heating system, absorbing an increased amount of solar energy and radiating it out.

Is it not conceivable that our altering of the planets surface is sufficient to have caused the rise in global temperatures?

It would be interesting if someone could post figures of percentage land use across the U.K. - could someone calculate the percentage of the land area covered in tarmac/concrete?

If my theory is in any way plausible, then perhaps global temperature could be correlated against world population or total developed land area.

[Yeti]

Not sure about the radiation idea tbh, but it's certainly possible that *some* climate data has been construed to look higher because of the urban heat island; i.e. 100 years ago a site may have been relatively isolated, and if now it has been engulfed by urbanisation, it will give a higher reading.

Then, of course, there are the secondary effects of building cities such as deforestation which increases atmospheric CO2.

Thinking about it though, I would imagine that any heat that tarmac does radiate out into space, acting like a mirror (and it's pure speculation) would actually lower temperature as more heat would "bounce back" away from the Earth.

[jethro]

With the human race altering ever increasing amounts of the Earth's surface, I have always wondered if the urban heat island effect could be affecting global temperatures.

Take London as an example - on satellite photos it never fails to amaze me how massive the urban area actually is. The fact that we can see London from space shows just how significant it is. Now take all the other major urban areas, roads, and other man made surfaces, and you can see the big picture. Surely all of this across the entire planet acts as a massive central heating system, absorbing an increased amount of solar energy and radiating it out.

Is it not conceivable that our altering of the planets surface is sufficient to have caused the rise in global temperatures?

It would be interesting if someone could post figures of percentage land use across the U.K. - could someone calculate the percentage of the land area covered in tarmac/concrete?

If my theory is in any way plausible, then perhaps global temperature could be correlated against world population or total developed land area.

This guy has done lots of work on UHI, have a look around his site, it may provide you with some answers.

http://www.climateaudit.org/

[LadyPakal]

Have a look here, it's an illuminating ongoing project looking at US surface station siting:

http://www.surfacestations.org/

I found this very interesting - scroll down to fig 2-5.

http://www.appinsys.com/GlobalWarming/GW_P...TempMeasure.htm

Then watch this animation to illustrate the above graph:

http://climate.geog.udel.edu/~climate/html...ghcn_T_stn.html

Animation is linked from here:

http://climatesci.org/2006/12/19/land-surf...ange-over-time/

Comment 6 made me wonder...

It's all very interesting and leaves me wondering exactly how much we can trust any of it.

[Chris Knight]

Have a look here, it's an illuminating ongoing project looking at US surface station siting:

http://www.surfacestations.org/

I found this very interesting - scroll down to fig 2-5.

http://www.appinsys.com/GlobalWarming/GW_P...TempMeasure.htm

Then watch this animation to illustrate the above graph:

http://climate.geog.udel.edu/~climate/html...ghcn_T_stn.html

Animation is linked from here:

http://climatesci.org/2006/12/19/land-surf...ange-over-time/

Comment 6 made me wonder...

It's all very interesting and leaves me wondering exactly how much we can trust any of it.

Ahh, trust - it is such a wonderfully human, if not totally a scientific term.

[LadyPakal]

A tad condescending...

Every scientist should be able to 'trust' (maybe you'd prefer the word 'believe') that the data he is using has been recorded correctly.

[Chris Knight]

A tad condescending...

Every scientist should be able to 'trust' (maybe you'd prefer the word 'believe') that the data he is using has been recorded correctly.

Here's a wonderful quote from R.A. Pielke Sr.'s home page:

“Koutsoyiannis et al. (2009) claim that climate is not changing due to human activities (climate is “naturally trendy”: Cohn & Lins, 2005), and that climate models do not provide a credible basis for assessing possible future impacts.

Rather than "deniers" or any other soubriquet, those who doubt AGW should be known as "Naturally Trendy People"

[cheeky_monkey]

Thinking about it though, I would imagine that any heat that tarmac does radiate out into space, acting like a mirror (and it's pure speculation) would actually lower temperature as more heat would "bounce back" away from the Earth.

as somebody who works in construction the opposite is true. Tarmac acts like heat sponge because of its make up and its colour, not only does it absorb solar radiation..it also gains heat relative to its surroundings through friction of moving traffic..much more than concrete roads. However the area of tarmac roads globally is minute and in terms of heat gain it is most effective during the summer months.

[LadyPakal]

I remember a road trip - open top car. As we arrived in Vegas and slowed down due to the traffic, the heat was tremendous and it mostly seemed to be coming up from under the car. The car thermometer was quite a few degrees higher than it had been in the desert just a few miles away. I think it was in the low 40's in Vegas that day.

Walking across dark tarmac covered parking lots was much hotter than the relatively cool sidewalks.

Standing beside Treasure Island watching the pirate ship battle was a pleasure because of the cool water misters along the pavements.

However, just how much of the temp increase was due to the massive air conditioners the huge hotels have on 24 hours a day, I have no idea!

Anecdotal I know, but I thought it was interesting.

Edited April 8, 2009 by LadyPakal

[Android]

Setting any lag time aside, remember that you need an increase in urbanization to cause an increase in warming. Just as you need the sun to increace in output or greenhouse gases to increase in concentration for an increase in warming.

ie if UHI stays the same it won't result in a warming trend. If London, or rather the area of london around a temperature sensor, has had about the same level of "urbanness" for 30 years, which is probably true, then in that time period UHI shouldn't have contributed much if any to any increase in warming.

Chinese cities on the otherhand have been built up recently and so they have gone from low UHI to high UHI in a short space of time that will cause a larger increase in temperature at those locations.

[Chris Knight]

Setting any lag time aside, remember that you need an increase in urbanization to cause an increase in warming. Just as you need the sun to increace in output or greenhouse gases to increase in concentration for an increase in warming.

ie if UHI stays the same it won't result in a warming trend. If London, or rather the area of london around a temperature sensor, has had about the same level of "urbanness" for 30 years, which is probably true, then in that time period UHI shouldn't have contributed much if any to any increase in warming.

Chinese cities on the otherhand have been built up recently and so they have gone from low UHI to high UHI in a short space of time that will cause a larger increase in temperature at those locations.

Not exactly true that you need an increase in urbanisation for the heating potential to increase:

The vertical profile of city centres change, invariably towards taller buildings, increasing the potential to warm from early morning and late evening sun, where the rays fall perpendicular to the buildings. Taller buildings mean more people per square metre, more journeys per day, more work equipment for the added personnel, more heat to get rid of in summer, more space to keep warm in winter. The downside is longer shadows. More people working in city centres requires longer commuting times, and increasing housing concentration in the suburbs. Supplies and services increase for increased populations.

Suburbs change - gardens become hard-standings for vehicles, warmer suburbs lose lawns and shrubberies to mediterranean patios and decking. Overgrown areas are made more "manageable". Roadside trees are removed when they become a cause of uneven pavements or blocked drainage gulleys, and remain unreplaced.

Buildings darken with age due to dirt, algae and weathering of surfaces, decreasing the albedo.

Warmer cities get upgraded with added air conditioning, older air conditioning units get upgraded by more efficient air conditioning units.

Urban areas are far from static, and rarely shrink.

[SleepyJean]

I have wondered about this aspect of things myself. Never mind the thermometers becoming engulfed by urbanisation, never mind the effects of concrete and tarmac, or the use of fossil fuels increasing co2 emmissions. There are millions of air conditioning units pumping out heat during the summer, and heating systems pumping out heat in the winter months. Where does that heat go? It doesn't just disappear, does it?

Supposing the co2 has nothing to do with? Supposing we are simply and purely heating up our planet with heat! Would that not tally with the highest rises being in the northern hemisphere, where there are more populated areas in temperate areas of the planet?

Ok, that's just my thoughts. I'm off to look at all the websites mentioned above now....

[Devonian]

Not exactly true that you need an increase in urbanisation for the heating potential to increase:

The vertical profile of city centres change, invariably towards taller buildings, increasing the potential to warm from early morning and late evening sun, where the rays fall perpendicular to the buildings. Taller buildings mean more people per square metre, more journeys per day, more work equipment for the added personnel, more heat to get rid of in summer, more space to keep warm in winter. The downside is longer shadows. More people working in city centres requires longer commuting times, and increasing housing concentration in the suburbs. Supplies and services increase for increased populations.

Taller buildings also mean more shade - so their net effect must be closer to zero. I remember walking it the city of London in the morning - cold and windy it was....

Suburbs change - gardens become hard-standings for vehicles, warmer suburbs lose lawns and shrubberies to mediterranean patios and decking. Overgrown areas are made more "manageable". Roadside trees are removed when they become a cause of uneven pavements or blocked drainage gulleys, and remain unreplaced.

Buildings darken with age due to dirt, algae and weathering of surfaces, decreasing the albedo.

Warmer cities get upgraded with added air conditioning, older air conditioning units get upgraded by more efficient air conditioning units.

Urban areas are far from static, and rarely shrink.

Yes, but are roads and building warming with time? Because if UHI is then they must be as well. Somehow I just can't see it.

No, I think there is UHI set up by a city but, as Android says, for UHI to increase over time a city has to get bigger over time.

[cyclonic happiness]

I have seen at first hand the urban heat island effect.

Where we live in bedworth, we sit on a hill and if i ride 4 miles to the west i have a good view of Birmingham.

i have sat on that hillside often and looked over the valley towards Brum and seen the towers of thunderstorms rocket as the drifted over Brum towards coventry and Nuneaton & Bedworth.

Some days the forecast has said that we were for light showers, but the modified showers from Brum are really really severe and very localised within the belt directly in line with us and Brum.

[Chris Knight]

Taller buildings also mean more shade - so their net effect must be closer to zero. I remember walking it the city of London in the morning - cold and windy it was....

It's called the 'canyon effect', and research has shown the effects are real with regard to nocturnal heat retention in urban areas.

I wish you would back up your thoughts with more than just personal anecdotes, Dev, not like you at all!

Yes, but are roads and building warming with time? Because if UHI is then they must be as well. Somehow I just can't see it.

No, I think there is UHI set up by a city but, as Android says, for UHI to increase over time a city has to get bigger over time.

The Metoffice has a nice article on microclimates.

The increase over time is a positive feedback, an overall knock-on effect, and particularly noticeable when mean temperature is calculated from maximum and minimum temperatures, rather than integrated dT.

[Methuselah]

A tad condescending...

Every scientist should be able to 'trust' (maybe you'd prefer the word 'believe') that the data he is using has been recorded correctly.

So, why do deniers appear to trust no one...Too many X-Files? <_<

[LadyPakal]

Could be - personally I find that those using specific terms to denigrate lead to a loss of trust from me.