Finally – an honest quantification of urban warming by a major climate scientist

This is a small bombshell. I’ve been telling readers about UHI since this blog started. One notable example that I demonstrated by actual measurement is Reno, NV:

Click for larger image

The IPCC reports have minimized the effects of UHI on climate for quite some time.

From Warwick Hughes:

The IPCC drew that conclusion from the Jones et al 1990 Letter to Nature which examined temperature data from regions in Eastern Australia, Western USSR and Eastern China, to conclude that “In none of the three regions studied is there any indication of significant urban influence..” That has led to the IPCC claim that for decades, urban warming is less than 0.05 per century.

A paper in JGR that slipped by last fall without much notice (but know now thanks to Warwick Hughes) is one from Phil Jones, the director of the Hadley Climate Center in the UK. The pager is titled:  Urbanization effects in large-scale temperature records, with an emphasis on China

In it, Jones identifies an urban warming signal in China of 0.1 degrees C per decade.  Or, if you prefer, 1 degree C per century. Not negligible by any means. Here is the abstract:

Global surface temperature trends, based on land and marine data, show warming of about 0.8°C over the last 100 years. This rate of warming is sometimes questioned because of the existence of well-known Urban Heat Islands (UHIs). We show examples of the UHIs at London and Vienna, where city center sites are warmer than surrounding rural locations. Both of these UHIs however do not contribute to warming trends over the 20th century because the influences of the cities on surface temperatures have not changed over this time. In the main part of the paper, for China, we compare a new homogenized station data set with gridded temperature products and attempt to assess possible urban influences using sea surface temperature (SST) data sets for the area east of the Chinese mainland. We show that all the land-based data sets for China agree exceptionally well and that their residual warming compared to the SST series since 1951 is relatively small compared to the large-scale warming. Urban-related warming over China is shown to be about 0.1°C decade−1 over the period 1951–2004, with true climatic warming accounting for 0.81°C over this period.

Even though Jones tries to minimize the UHI effect elsewhere, saying the UHI trends don’t contribute to warming in London and Vienna, what is notable about the paper is that Jones has been minimizing the UHI issues for years and now does an about face on China. And even more notable is that Jones result are directly at odds with another researcher at Hadley, Dr. David Parker.

It seems that Parker is looking more and more foolish with his attempts to make UHI “disappear” To back that up, the National Weather Service includes the UHI factor in one of it’s training course ( NOAA Professional Competency Unit 6 ) using Reno, NV.

In the PUC6 they were also kind enough to provide a photo essay of their own as well as a graph. You can click the aerial photo to get a Google Earth interactive view of the area. The ASOS USHCN station is right between the runways.

reno-nv-asos-relocation.jpg

This is NOAA’s graph showing the changes to the official climate record when they made station moves:

reno-nv-asos-station-moves-plot.png

Source for 24a and 24b: NOAA Internal Training manual, 2004-2007

What is striking about this is that here we have NOAA documenting the effects of an “urban heat bubble” something that Parker 2003 et al say “doesn’t exist“, plus we have inclusion a site with known issues, held up as a bad example for training the operational folks, being used in a case study for the new USHCN2 system.

So if NOAA trains for UHI placement, and Hadley’s Dr. Jones admits it is real and quantifies it, I’m comfortable in saying that Parker’s claims of UHI being negligible are pure rubbish.

Its all about location, location, location. And climate monitoring stations that are poorly sited and that have been overrun by urban growth clearly don’t give a pure signal for assesment of long term climate trends. This puts a real kink in the validity of the surface temperature data in GISS and HadCRUT and could go a long way towards explaining the divergence between satellite and surface temperatures in recent years.

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Stephen Wilde

A problem arises in that if UHI effects could account for much if not all of the observed warming then where does that leave the supposed effects of a high level of solar activity and a positive PDO with an exceptional dominance of El Nino during the same period ?

Chris R

Roger Pielke Sr. strikes again: Land use IS a first-order climate forcing after all!

Malcolm

Correction: This is a MAJOR BOMBSHELL.
Though the science may be considered minimal the politics surrounding this issue are huge. The IPCC and their reports have taken a direct and massive hit on this matter and the sooner that news is broadcast to the IPCC and worldwide the better.

Denis Hopkins

That is very interesting. Also interesting that Geography departments in schools discuss UHI yet, in the main, do not relate it to the “warming” of AGW.
It would be helpful if Exam Boards were to introduce a discussion section on this and for schools’ publishers to use these examples as discussion points. The physics syllabuses have been overrun with discussion points to the exclusion of any “hard, mathematical” points. The discussions they suggest are so contrived and puerile. One on the effects of UHI on the climate models would be valid in the context of real discussion and argument.
Perhaps we could try a research project to see the effects of man in producing heat islands and how that can lead to catestrophic warming. If they see “man” and “catestrophic warming” in an application I am sure it would get funding!

ak

what is the percentage of sites that are in urban vs. non-urban locations for GISS and HadCRUT?
if a site has always been in a city, the data is still valid for showing the temperature at that location and likewise, the temporal trends. should we stop using data from a site because in 1940 it was in a field and a forest has grown up around it since?

Ron Michaels

This should only show that the land monitoring sites are affected not the satellite measuring and possibly explain some of the difference in them. The Solar activity, PDO changes, etc are an explaination of the changes in temperature which is happening all of the time.

Mark Fawcett

“Urban-related warming over China is shown to be about 0.1°C decade−1 over the period 1951–2004, with true climatic warming accounting for 0.81°C over this period.”
Mixing units like this requires some care when reading; at first glance they appear to minimise the UHI contribution. However, let’s put them in the same ballpark:
UHI = 0.1C per Decade
Climatic warming = 0.81C per 53 years = 0.15C per Decade
Now that’s something that should be shouted about – I make it that UHI is therefore responsible for ~40% of the “measured” temp rise per decade at certain sites.
No doubt this “won’t affect the trend – it’s robust”
Mark.

ak

does the 0.81C of observed warming in china include the 0.1C/decade urban effect? or is that in addition to that number?
or for the the ~50 years of the study is it:
0.81 = (0.1C/decade * 5) + 0.3C
or
1.31C = 0.81C + (0.1C/decade * 5)
sorry it’s not quite clear to me

Dave Day
Antonio San

“We show examples of the UHIs at London and Vienna, where city center sites are warmer than surrounding rural locations. Both of these UHIs however do not contribute to warming trends over the 20th century because the influences of the cities on surface temperatures have not changed over this time.”
Obviously there is quite a contradiction here: so year 2000 London’s UHI contribution over the XX century of greatest expansion, use of fossil fuels, industries, cars etc… has not changed compared to 1900 London? Well Dr. Jones that’s a good news -if you are right- because since we are also told that cities are the biggest CO2 “polluters” -if CO2 is supposed to be a pollutant- as seen on the google map of CO2, then Londoners should rest: they are not responsible for global warming or climate change. Viennese idem. Parisians probably too! Yahoo: we’re off the hook; please charge your carbon tax to someone else…

Juraj V.

Compared with satellite measurements, up to half of warming observed by ground stations during the last 30 years may be caused by UHI. This is kind of “unconvenient truth”, since in the period 1910-1940 (low CO2 growth), observed warming rate was steeper than in 1977-2003 (higher CO2 growth).

Jim

In December I took a drive from Durham, NC to a state park north of Winston-Salem for a planned day hike. The downtown air temp when I left at 4am was 12F degrees per our local weather station.
My initial car temp gauge was showing 14F in my driveway but quickly dropped to 8F as soon as I got on the freeway out of town. As I drove through Burlington it climbed to 10F. Out of the city it fell back to 8F. When I drove through Greensboro the temp rose to 11F. Out of Greensboro it fell back to 8F. When I entered Winston-Salem it climbed to 10F and dropped to 7F upon leaving town.
Anecdotally, the temp gauge rose from 8F to 10F while out on the open (8F)road, but following 2 semi-trucks. As soon as I passed them the temp decreased back to the 8F ‘background’.
So there is little question in my mind that city UHI’s exist and the effect is quite visible in the coldest part of the early morning when human activity is at a minimum. To say that UHI’s have virtually no effect is non-sensical. Any model that does not contain significant UHI adjustments in there temp predictions is also non-sensical.

John Galt

@ Stephen Wilde (07:42:59)
I can’t tell you how all the pieces of the puzzle go together. I can say that the IPCC doesn’t have it right and the prevailing assumption of AGW through greenhouse gas emissions — especially CO2 — is falsified by all the evidence.
By my count, at least half the warming is due to ocean currents, half is due to UHI, half is due to changes in the sun, etc.
Does that mean these factors don’t influence our climate? By all means, no! That the evidence is contradictory means we don’t have a good understanding of the climate system.
Since climate is complex and chaotic, this is quite understandable. That fact that nobody can really explain the climate and the observed changes over the last century, reinforces the fact that the IPCC is incorrect.

MattE

For all the money going to climate science, why doesn’t someone actually just study UHI? Take a 100 thermometers, spread them out over a grid in a city and surrounding countryside and measure temps for a year. Viola. Of course then they’d actually “know” the answer they might not want to hear.

EW

Did you know, that the 19th century geneticist Gregor Johann Mendel (of the pea fame) also made a quick excursion in the climatological realm? And his observations concerned UHI in the city of Brno.
http://www.amet.cz/webmendel/GJMurbanenvironment.pdf

Aron

Whenever Groucho Marx returned from the UK and was asked how did he find things in London, he used to reply “The fog lifted and there everything was!”
Since the late 80s London is no longer known for fog. I can’t remember an instance of the type of fog that I grew up with. That fog I knew was dew mist, which was nothing compared to what Londoners lived with for several hundred years before the Clean Air Act. That fog was smog – a dense and poisonous mix of particulate matter from millions of chimneys of homes and factories, as well as dirt.
Under such conditions there was no chance for sunlight to penetrate to ground level as much as it does today. There was also less urban infrastructure to absorb and maintain heat. No asphalt, no tar roads, no concrete pavements. It was nearly all wood, earth and stone.
So when Dr. Jones tries to downplay London’s UHI and the effect of the Clean Air Act on heating the city and surrounding areas, he is simply incorrect (I want to use harder language but am not in the mood). He has no ground to stand on to make such claims that London’s UHI is negligible.
London is not a unique case either. Liverpool, Edinburgh, Dublin, Paris, New York, and other major cities have an identical history of urban changes and reduced air pollution.
A side note to those who believe humans have overpopulated the planet and other Malthusian ideas: London’s population today stands at half a million less than it did in the 1930s. This is despite increasing its territory by eight times and a large influx of immigrants since the 1950s. There is less urban sprawl and more space per capita. There is less homelessness, less poverty, less class division and less disease.
Contrast that with the various experiments with socialism that have taken place around the world. China and India are two good examples where socialism resulted in lower standards of living, widening class division, disease, famine and very high birth rates. India was rescued once by the Green Revolution (not to be confused with today’s Greens. The founder of the original revolution detests modern environmentalists), and then had to rescue itself again.
If it weren’t for the free market reforms of the 90s both nations would have faced disasters that even global warming alarmists can’t imagine (and if they could they would blame it on everything but socialism).
The moral of the story is that government should stick to defence and policing and leave most of the rest to the free market, only stepping in when absolutely necessary. The global warming hysteria is an example of government and politically motivated organisations overstepping the mark.

Marc

Mostly unrelated to this topic but I had to share.
A week or two ago XKCD posted a cartoon about correlation everyone here should note.
http://xkcd.com/552/ When you hover your mouse over the image you get this text.
“Correlation doesn’t imply causation, but it does waggle its eyebrows suggestively and gesture furtively while mouthing ‘look over there’.”
Too many researchers are seduced by ‘Correlation’.

Roger Knights

It seems to me that it wouldn’t cost much or take a lot of staffing to do studies of UHI effects, and that there could be a lot of bang for the buck in the results (whichever way they turn out). (Even college or high school kids could do some of them as a project.) This is the “unknown” that could be most quickly resolved. So I hope .1% of that money intended for climate modeling supercomputers gets diverted into this area.

LAShaffer

What I don’t understand is why they have been ignoring obvious heat sources if they are really looking for reasons for the surface temps allegedly rising. Fossil fuels (stored chemical energy) are brought to the surface and BURNED. Looks like heat to me. According to the 2007 world energy outlook, the rate at which we were burning those fuels was ~14billion Btu’s/sec. Not shabby. Now consider that since the early ’90s, nearly the entire world has been on the largest building binge in history. The oil that was not worth burning was poured onto highways and rooftops during this building extravaganza. There has to be multiple tens of millions of extra acres now absorbing massively larger amounts of sunlight than they did when they were covered by plant life, or sand, or even ice and snow. Where do these people think all of this heat is going?

Tom_R

The past decade has forced the warmists to admit that natural climate variations are at least as strong as the theoretical CO2 warming (N >= CO2). Now that a significant UHI effect is added to the warming makes:
N >= CO2 + UHI,
or
CO2 <= N – UHI.
That doesn’t leave much of the late 20th century warming to be contributed by CO2.

Michael D Smith

Anthony –
A little OT but *.wordpress.com items are blocked at my office but wattsupwiththat.com is not… If you were to store images at WUWT instead of .wordpress.com, I could see them… If this would be a convenient change, great… If not, I understand, worth asking.
I post stuff from WUWT on my wall pretty often, but I can’t get the pictures. This article would be a good one. Thanks, Mike S.
Reply: Answered via email ~ charles the moderator

Retired Engineer

I wish I could find the reference. A visiting professor at CU Boulder did a study on U.S. cities that have grown and those that have not, from about 1970 to the min 90’s, study published in late 90’s. Surprise, the cities that grew had the greatest increase in temperature, cities that had not increased in population had little or no temperature change. The prof’s name was Bitte or something like that. Probably got ridden out of town on a rail for contradicting what ‘everyone knows.’

Robert Wood

Satellite data.

Adam from Kansas

No doubt the UHI effect in some chinese cities would be simply massive, all you have to do is look at their mega cities like Chonquing, Shenzen, Shanghai, and Ghangzhou. I think the spelling on some of them may be a tiny bit different, but huge cities like those mean big UHI.

Bob

I don`t get it, why would Jones publish such a study.

Josh

That’s just it, Stephen. All of the “science” involved in proving and/or disproving man’s influence on climate is clearly NOT settled. There are so many variables and unknowns that it is ignorant at best to state AGW is real. At worst, it is a blatant attempt to control population and wealth through lies and propaganda.
Personally, I don’t believe CO2 is doing anything to the overall temperature trend of the earth. I don’t even know if it’s possible to determine with any accuracy what that trend is or should be. Even if we could determine that, I don’t think there is any way to accurately measure it. For example, do we just continue what is done today – (high temp. + low temp)/2? Should we take hourly readings and divide that sum by 24? Should we measure temperature to the hundredth of a degree? Thousandth?

Allen63

I think the UHI effect was intuitively obvious — just didn’t know how much of an effect. Its probably a larger impact than indicated in the report — since its a Hadley report, and its intuitively obvious they will minimize the effect (if for no other reason than peer pressure).
None the less, I applaud Phil Jones and Hadley for the report.

Aron

Remember too that Shanghai suffers from dense smog. When that clears up the city will receive more sunlight and heat up. That from reducing air pollution!

Yep. Kudo’s to Phil Jones for admitting the obvious.

Alan the Brit

I live in a part of rural Britain, south-west England to be accurate. At the risk of some repetition, during the winter when I used to have to pick up my son or daughter 8 miles away in the provincial city, my car’s air-con system would read something like -0.3C, flashing the ice warning. After a couple of miles, allowing for wind friction over the sensor, the temp reading would read something like -0.1C, still flashing the ice warning. By the time I’d reached the outskirts of the city the temp reading is up to 1.0C, & in the city centre it would read 2C! So the heat island effect is real. Everyone I know seems to remark on the same thing during any winter, mild of otherwise, it’s warmer in the city than in the countryside. Whether this “real” effect is truly accounted or “adjusted” for is unknown.
Is there still some enthusiasm to check the UK weather stations on the cards? I would certainly help on the south-west stations. As said before we may encounter restrictons as we’d be accused of spying for terrosist organisations or something ridiculous, but we could have a go! Does anyone know if the CET station system accessible to the public?

Tom in Florida

Perhaps we should look at UHI effect as local weather rather than indication of climate change. I also think we need to distinguish between real temperature increases and measured temperature increases due to UHI effect.
As Anthony has shown, the supposed increases are most likely caused by bad measurments due to siting issues rather than real temperature increases of the climate.

peterxema

I have two questions that have been bugging me for some time. Firstly, is there any accessible info on what proportion of global air temperature recording stations are in urban/airfield locations as against open (not forested) rural locations? Secondly, given that the UHI effect can be so strong, has anyone in, say, Europe or North America constructed and compared temperature trends for these two different environments over the past 50 years or so (and making allowances for land elevation effects)?

MattN

Lemme see if I can guess RC’s response.
“It doesn’t matter…”

TJA

Satellite data

“This should only show that the land monitoring sites are affected not the satellite measuring

This is not true. Satellite measurements are adjusted and calibrated using surface temp records. So UHI also contaminates satellite data. It would be nice if this were as simple as Al Gore and Gavin Schmidt say.

where does that leave the supposed effects of a high level of solar activity and a positive PDO with an exceptional dominance of El Nino during the same period ?

If we are on a long term cooling trend, due to orbital factors, which is likely due to the fact that our current interglacial is somewhat long in the tooth, then it means nothing with regards to those issues.

TinyCO2

I don’t know if anyone has mentioned this before but there is a study of UHI in the UK currently underway. Reading, Manchester, Belfast, Birmingham, Cardiff, Exeter, Glasgow, Oxford, Sheffield and more cities are due to be surveyed under a Royal Meteorological Society experiment. There’s a very nice picture of Manchester’s UHI.
http://www.metlink.org/urban/background.php
I’m not entirely sure what they intend to do with the information but the goals of the hosting organisation seem very compatible with the intentions of the good people here a WUWT and Surfacestations.org
More specifically, the meteorological aims of the project are to:
. improve individuals’ abilities to collect and record weather data;
. appreciate weather differences from region to region;
. understand the reasons for the differences.
The long-term benefits of MetLinkInternational are seen as:
. a wider interest in the teaching of meteorological topics at both primary and secondary levels;
. a greater awareness of, and enthusiasm for, meteorology as a science-based subject;
. the recognition of meteorology as one of the few fields of study that can embrace the full scope of experimental method, scientific analysis and interactive ICT skills in an engaging way;
. the acquisition of a meteorological information and data resource which will be of value long after the project has ended.

John

Can someone explain to me how surface station readings impact satellite readings (in laymans terms)? I’m curious to understand it better.
I assume that the past 10 years or so, the impact would be smaller? the UAH readings have been higher this year than last – I assume UHI issues wouldn’t impact that?
Thanks for any info.

Tim McHenry

Ditto to what Jim, Allen63 and others have been pointing out. Am I missing something? Isn’t this all just common sense? Our local weather broadcasters routinely say things like, “Low of 40 in the city, you may get to mid-30’s in outlying areas.” Anyone with an eye, half a brain, and a temp-gauge can tell that it gets colder outside the city. Combine that with the expansion of the cities around the temp stations over time and you have a factor that simply MUST be taken into account for any accuracy in the record!

Robert Wood

TJA @10:10:47
This is not true. Satellite measurements are adjusted and calibrated using surface temp records
Can anyone tell me or show me how?

Robert Wood (09:01:09) :
Satellite data.
I don’t think they heard you. RW has a point, folks. What about the trend in the satellite record?

crosspatch

I disagree with the notion that areas that are already built up won’t show an increase in warming over time. In other words, the statement:
“Both of these UHIs however do not contribute to warming trends over the 20th century because the influences of the cities on surface temperatures have not changed over this time.”
Is an assumption, not an observation. Look at London in the early 20th century. What did the roofs of the buildings look like and what material was used on them? What did the road surfaces look like? I would be willing to bet that there was more concrete and cobblestone where there is asphalt “black top” today.
One must not only consider the density of development but also the impact of materials used as they change over time. For example, it has been estimated that the use of “cool roofs” and “cool pavements” could reduce the Los Angeles heat island by 1 to 2 degrees in summer. Were the roofing and paving materials in use in 1900 “cooler” than the materials being used in 1999? How has the albedo changed? What was the impact of smokestack output on solar heating of these surfaces in the early 20th century and with clearer urban skies today, are we seeing more solar heating of these surfaces resulting in more heating?
To simply state that the urban heat island signature is doesn’t change of the course of the century ignores changes that have taken place over that century that can greatly impact the UHI signature. No evidence is given to support the notion that there is no change over time in London or Vienna. It is simply an assumption pulled out of thin air.

Adam

TJA (10:10:47) :
“Satellite measurements are adjusted and calibrated using surface temp records. So UHI also contaminates satellite data.”
No. I believe that it has even been discussed on this blog before that satellite measurements are NOT calibrated using surface temp records. Although, what is interesting, is that satellite (RSS and UAH) anomalies are highly correlated to those from GISS and HADRUC…
http://tamino.files.wordpress.com/2008/03/4way.jpg
So, where does the warming trend come from in the satellite data??

Indiana Bones

This is somewhat OT – but funny and related to the movement toward acceptance of AGW as myth:
http://newsbusters.org/blogs/p-j-gladnick/2009/03/18/global-warming-alarmist-irked-cold-weather

George Patch

All I can think of is “Duh”
UHI seems like an obvious concern with urban stations or stations being encroached upon by development, but somehow it is largely dismissed as a “Red Herring” when ever the subject comes up in climate circles.
Maybe the thought is local weather is not climate, but it is when you have enough of it.

Carter

Sort of OT, unless you consider all that asphalt that tends to be found in cities. Long time lurker here, but talk of UHI reminded me of a conversation with my 9 year old son yesterday.
One of the first really nice warm sunny days in Ontario so far this Spring. Driving with my boy, who had his window down. He made a comment about how much his black jeans were absorbing the heat of the sun, which felt good compared to the cool air coming in his window as we drove. He was chattering away about how much heat the colour black absorbs compared to lighter colours (totally without my input, BTW). So I asked him “So if black does such a good job absorbing heat, do you think it’s a good idea to put a thermometer close to a road?” His answer: (with the kind of incredulous superiority in his voice that only a kid can deliver) “Duh! Any moron knows that won’t work. The road will make it hotter.” Mr. Parker… nuf said.

hotrod

MattE (08:19:14) :
For all the money going to climate science, why doesn’t someone actually just study UHI? Take a 100 thermometers, spread them out over a grid in a city and surrounding countryside and measure temps for a year. Viola. Of course then they’d actually “know” the answer they might not want to hear.

I was having the same thought when I saw you had made the above post.
This would be a wonderful science lab project for some interested college students.
I’m not sure how many of you remember the “Day in the life of ” photography projects, where hundreds of photographers tried to document daily life all over a single country on the same day.
Here is the concept I propose.
Working title – One days temperature profile project
Recruit about 30+ interested students to the project in a location.
Build 30 identical low cost Stevenson screen enclosures with identical thermometers which are calibrated to a common reference source like a water ice solution.
Select a relatively compact moderate sized city surrounded by rural areas.
Pre-plan a grid one or more measurement locations for the Stevenson screens that meet good sighting protocols with photo documentation and GPS coordinates.
Train the students how to set up the screens allow them to stabilize (ventilated screens would stabilize quicker), and record pre-planned temperature readings
Have all the students take temperatures at these pre-determined locations at simultaneous fixed time intervals on the same day.
That would allow you to produce a one day snapshot of the thermal profile for the entire grid area at very high resolution.
Repeat the exercise on several random days.
Some enterprising graduate student could write a thesis on this and do the world a major favor in documenting the daily thermal profile of a community at high resolution.
You could even include some “poor location measurement sites” like roof tops, near roadways etc as reference controls to show how badly such locations bias the apparent temperature of the city.
Any meteorology professors or related professions willing to organize such a One Days Temperature Profile project?
Larry

It seems to me that it wouldn’t cost much or take a lot of staffing to do studies of UHI effects, and that there could be a lot of bang for the buck in the results (whichever way they turn out). (Even college or high school kids could do some of them as a project.) This is the “unknown” that could be most quickly resolved. So I hope .1% of that money intended for climate modeling supercomputers gets diverted into this area.
No, at least 10% should be directed to UHI studies, with the bulk of that money going to the Surfacestations Project, the recognized pioneer and leader in such studies.
I did not purchase the article, and so did not read the citations. I can only hope that the work of Watts et al. was cited and credited.

Paul Wescott

Once again, the Hinkel study of the situation at Barrow, Alaska, is instructive, i.e., a community doesn’t have to be what is commonly thought of as “urban” to experience a significant UHI effect. Because Barrow roughly doubled in size since 1979 (to about 4,700), the increase in cold season average temps with UHI effect looks a lot like Dr. Mann’s hockey stick.
If the other high latitude stations in Alaska, most if not all on airports, are similarly affected, though likely less than fast-growing Barrow, the flat to negative temperature trend at http://climate.gi.alaska.edu/ClimTrends/Change/7708Change.html may in reality be a lot steeper negative.
ISER recently completed a study of economic consequences of climate change in Alaska. I warned them (pre-PDO shift) that examining nothing but positive temperature trends may leave us short of well-thought-out alternative adaptive measures if the climate instead cools. I guess they weren’t being paid to look at that possibility.
Paul

Don Keiller

Could this be Phil Jones trying to back-pedal in an effort to put “space” between him and an alleged fraud over a paper demonstrating the lack of UHI effect in China?
See http://www.informath.org/apprise/a5620.htm

ak (07:56:00) saith: “…if a site has always been in a city, the data is still valid for showing the temperature at that location and likewise, the temporal trends. should we stop using data from a site because in 1940 it was in a field and a forest has grown up around it since?”
Great point, ak. The answer is clearly ‘yes,’ especially if it’s a forest of buildings. Yes, UHIs will not affect (*) any current short-term trends. But they’ve already affected the long-term trends (1940 to present) that are used to pretend to show AGW. Something else must now be done to add more fictitious AGW at the same high rate. Something like, say, tampering with the old records. Do we know anyone who would do such a desperate thing?
(*) exception: heavy asphalt coverage will accentuate even short-term urban heating trends. On a very hot day, asphalted areas can jump ~20°F when the rest of the city is only going up ~10°F. Too bad if there’s a sensor there.
And don’t forget, guys. On April 1, everybody move your BBQ another three feet closer to the sensor. (jk)

MattN (10:10:46) sez: “Lemme see if I can guess RC’s response: ‘It doesn’t matter…’
or “UHI is an outmoded concept.”