Reposted from Dr. Roy Spencer’s Global Warming Blog
November 10th, 2022 by Roy W. Spencer, Ph. D.
Now that I’m back to researching the surface air temperature record and the Urban Heat Island (UHI) effect, I decided to revisit the temperatures in Las Vegas, Nevada. It’s been over 8 years since I posted about Las Vegas being the poster child for the UHI effect and I showed some warming trend calculations from the hourly temperature data at McCarren International Airport (now Harry Reid International Airport… not kidding) which suggested that much of the warming there has been from the urban heat island, not global climate change.
And this is the trouble with monitoring global climate trends — most of the land data are gathered where people build things… increasingly so. In June of last year, The Guardian, predictably, conflated the urban heat island effect with climate change when it stated,
“Driven by the climate crisis and intensified by the city’s expansive growth, Vegas is already cooking — and it is going to get worse.”
Many people don’t really make a distinction between the two. It is reasonable to ask the question, how much has the region around Las Vegas warmed in the last several decades, compared to in the city itself? The trouble is that there are few hourly temperature measurement locations with data extending back at least 50 years in the region that are rural in nature. The area is, after all, a desert, and people don’t usually choose to live in such locations.
I computed 50-year trends for Las Vegas and for a rural Nevada station, Winnemucca from 24-hourly data, which allows us to see how the trends change with time of day. I did this for the warmest half of the year, April through September. The following plot shows a remarkable feature… the strong warming in Las Vegas has been entirely at night. Winnemucca shows the background climate signal, with fairly uniform (and weak) warming trends throughout the day. But the impervious surfaces in Vegas — buildings, concrete, asphalt — absorb more sunlight during the day than the surrounding desert, and then at night release that heat into the air.
Part of the reason this happens is the albedo of the city is lower than that of the surrounding desert (thanks to Anthony Watts for reminding me of this). But at least as important is that fact that concrete has a thermal conductivity 9 times as large as sand does, so when it is heated by the sun, much more energy is stored down into the pavement. Sand would have gotten exceedingly hot, but just at the surface, and the extra energy would radiate away (infrared) as well as drive stronger atmospheric (dry) convection which would carry that heat away during the daytime.
Why would such a thing not show up during the day just as well? Because turbulent mixing driven by a strong super-adiabatic lapse rate near the surface spreads the heat up through the atmosphere and cooler air comes down to replace it, cooling the city during the day. But then at night, a temperature inversion forms, and the lowest levels of the atmosphere no longer exchange energy convectively with higher altitudes. In effect, the strong nighttime inversion that naturally occurs in the desert has weakened over the city as the pavement releases the extra energy it has stored during the day.
The actual background climate warming in the last 50 years in Las Vegas (whatever its cause), based upon the above plot, looks to be around 0.25 deg. C/decade. This is also part of the reason why it is important to monitor global temperature trends with satellite measurements of the deep troposphere — it provides a more robust measurement that is not as influenced by surface effects, such as the Urban Heat Island, and avoids conflation of Las Vegas heat with the “climate crisis”.
Very nice analysis. I posted a similar example using an evening transect of Phoenix from rural to downtown to rural and back (just noting the cars reported outside temperature) in essay When Data Isn’t in ebook Blowing Smoke. The later evening return thru downtown after dark was warmer than the earlier downtown. And now you have explained why.
Among other things, observationally shoots down the Zeke Hofstetter/BEST study claim that UHI is unimportant.
No on else in the climate industry thinks the UHI effect is unimportant or they would have removed their adjustments, although inadequate, from their analyses. After all, it would increase the heating rate. Watts’ analysis of US land temperatures using well-sited thermometers versus poorly-sited thermometers shows the effect as well.
How many thermometers in the Southern Hemisphere in 1850? Dr Roy has trouble finding an extra-urban comparator. What about a whole hemisphere? We only have half a degree to go before climate catastrophe. From where measured?
A few. Sidney AUS, Buenos Aries, São Paulo, Santiago, Capetown SA… enough to get a general land, not ocean, picture.
Half a degree to Climate Catastrophe?? Based on what provably erroneous model? 1.5C catastrophe was invented after Schellnhuber’s fanciful 2C catastrophe failed because EBM ECS was only about 1.7C.
Perhaps you were being sarcastic and forgot the /s?
Sydney not Sidney.
The mockery in the second-last sentence is pretty obvious, telegraphing satire undermines the whole point of it.
“Perhaps you were being sarcastic and forgot the /s?”
Seemed pretty obvious.
To most regulars here. But anyone who doesn’t know better might not see it that way, since they’ve been saturated with the climate propaganda for decades…
And remember what Phil Jones said about the normals for the ocean temperature for the SH.
Have to disagree with your “general land picture”. I argue because you cite Cape Town as a data point.
Cape Town has a unique climate, not replicated anywhere in Africa below the equator. I’m only a thousand miles north, and we do not even have the same rain season… nor have the people a hundred miles from Cape Town. Even the plant life is from different planets!
I mention this just to point out that Cape data gives you absolutely zero usable information about African, or even just southern African climate, thus any model that uses that data for hindcasting, is fishing from it’s own hole.
This just illustrates the problem with a “global average” temperature. It really doesn’t tell you anything about anywhere.
Half a degree, a degree, there is NO “climate catastrophe” that will happen.
What will they say if we reach their pulled-out-of-their-nether-region amount of “warming” (of the “average” temperature, and mostly in the coldest and driest air masses, and mainly at night) and nobody even notices any meaningful difference?!
They’ll just move the goal posts a bit further, and continue their wailing.
THERE IS NOTHING “CATASTROPHIC” ABOUT 1.5 DEGREES WARMER THAN THE “LITTLE ICE AGE” – the Little Ice Age climate is closer to a catastrophe than where we are now. Millions starved during the Little Ice Age for want of food when there were fewer than 1 billion humans to feed. Today we’re at or close to 8 billion to feed – we would probably see BILLIONS starve if the Little Ice Age climate returned. COOLING is the catastrophe, not warming.
And if we returned to the climate conditions of The Little Ice Age and massive human starvation DOESN’T result, the reason will be…FOSSIL FUELS!
I know the remark a out the “climate catastrophe” was probably sarcastic, but for the education of those who might be lurking here and don’t necessarily know better, please don’t feed the “warming = catastrophe” bullshit, especially using their arbitrary “line in the sand” set so it is close enough to keep their climate ghost story “scary.”
I don’t think that NOAA and the NWS should have any atmospheric measuring device within 20 miles of any city. The only place that needs right now weather conditions are airports.
and airports readings should not be incorporated into climate data.
20 miles is the MINIMUM distance. Even then, 20 miles is far enough that all kinds of differences in temperature can occur due to elevation, pressure fronts, geography, terrain, land use, etc. It’s why homogenization of temperatures is such a bad approach at trying to infill locations that have no measuring station.
Attached is a graphic of area temps in northeast Kansas for 7am on 11/11/2022. You can see as much as 3F differences in locations that are 20 miles apart. Trying to infill using surrounding stations is going to be as inaccurate as all git out. Uncertainty in such an infill would be far greater than the assumed 0.5C assumed for most stations (which is probably way too low for actual field instruments). Of course most climate scientists today assume all uncertainty cancels out so they would say uncertainty due to distance is insignificant.
“Part of the reason this happens is the albedo of the city is lower than that of the surrounding desert”
Albedo varies naturally anyway, but that doesn’t of itself create a trend. It’s true that there may be a period of development, where the albedo changes.
Here is a plot of the last 50 years at that Nevada airport. It shows rapid warming up to about 1995, and then stationary.
The real test of all this, of course, is the comparison between the ClimDiv average temperature for ConUS, airports and all, and that for the pristine USCRN locations. Here is the NOAA plot. It’s hard to make out, because the numbers are basically identical. Yet you’d expect USCRN at least to be free of UHI.
Your graph shows no “rapid warming”.
“The real test of all this, of course, is the comparison between the ClimDiv average temperature for ConUS, airports and all, and that for the pristine USCRN locations.”
Such averaging provides nothing of value.
“Your graph shows no “rapid warming”.“
Indeed. But Roy’s complaint was that UHI exaggerates warming. How can that be?
Stop averaging everything together and maybe you’ll find out.
Perhaps because Spencer is graphing hourly maximum’s and you are graphing monthly averages?
Try comparing apples to apples instead of to oranges.
In general, as an urban location gets bigger, taller, more developed and taking over more rural areas, more UHI results.
Your graph shows a warming trend from about 1970 up to about 2000 – ok, why? If you want to talk about UHI then you need to match that graph with one showing how the airport and surrounding areas have gotten more developed – there’s probably some nice Landsat pictures of the area and time frame that would help.
One would be hard pressed to explain the temperature DROP 1950-1970 from your graph – CO2 was rising for sure and certainly the area wouldn’t be getting LESS developed. But actually one would have to check to make sure.
Airports move into less densely populated areas as urban areas expand – leading to a cooling from previous temperatures. You have to look at the entire demographic situation to see what is going on. The period of 1950-1970 was a huge urban growth period in the US as population moved from rural, agriculture-oriented areas into the cities. This resulted in lots of larger airports relocating. It happened in Kansas City and Denver. I’m not sure about the overall picture but I’ll bet something similar happened in lots of places.
I love the way Nick tries to over simplify every problem to the point of meaningless.
When you only look at Vegas temperatures, you have no idea whether the temperatures in the region are going up down, or sideways.
Without subtracting the regional temperature trend, a simple examination of Vegas itself yields no useful data.
Picking short time periods, and then not comparing to nearby stations is what someone who doesn’t know what they are doing would do. Or someone who is trying to hide something.
What matters is what is happening in Vegas vs. what is happening in the nearby rural areas.
Ironically, UHI is, in part, the greenhouse effect, not The Greenhouse Effect.
The real “greenhouse effect” with the sun warming the objects inside the greenhouse, or the upholstery of your car, and the glass preventing the heat from leaving. With UHI, the concrete and asphalt are the upholstery and the temperature inversion and possibly lack of wind substitutes for the glass.
Nice work – thanks. However, note that UHI is purely anthropogenic. It is warming. It just isn’t global. And we’ll have to wait to see if it is catastrophic.
Yes Jim, but who’s got 1,000 years or so of life left to determine what might be in store.
Maybe we should just do what all our ancestors had to do –
make the best of the circumstances they were born into, and improved during their lifetimes?
ATheoK points out a good particular reason how it could be catastrophic, but in general the urban build up reaches a plateau and the effect levels off, even if the total urban area keeps growing in width and breadth. Increasing height would allow better cooling from wind and more surface area to cool from and block sunlight to the asphalt, so the effect levels off – maybe even decreases if fancy skyscrapers are topped with shiny metallic ornamentation.
Exactly, most of us have far larger things to worry about than a trivial change in temperature- not that we should totally ignore that issue but it’s not something to panic over and trash our economies and the strength of our nations. And, modern nations should know enough to avoid such cults after many centuries of being dominated by religions. Here in Massachusetts, this new cult is as fanatic as anywhere on the planet.
Obviously, you’ve never crossed a late July asphalt street, picked up melted tar on your sneakers, then tracking into a house across their rug. The rug was cream color to boot.
The lady of the house tracked me down, literally. Catastrophic is one word for the occasion… Mayhem is another.
Living in the dog house afterwards for weeks.
The footprints never came out and every now and then, blood would boil again.
I thought all Americans used their cars to cross the street to avoid all this sort of thing.
Way back in the day I used to inspect new pavement on Interstate construction. The hot asphalt comes off the truck at 220-290F, they generally do 8-12 inches in 2-4 inch lifts with finer grades on the top. Rain has to be taken into consideration as well as the contractor’s desire to get the job done. What will they use instead for Net Zero? Unicorn poop?
You need really good boots to walk on this stuff and they don’t last too long… After 8 hours you are ready for a really, really cold beer. Or two.
“note that UHI is purely anthropogenic. It is warming. It just isn’t global. And we’ll have to wait to see if it is catastrophic.”
And UHI has nothing to do with CO2.
It isn’t “climate change,” so it will never be “catastrophic.”
The only “climate catastrophe” humanity will experience is the descent into the next ice age. WARMING during an INTERGLACIAL period in an ICE AGE (which is, geologically speaking, where we currently are) is GOOD NEWS, not a “catastrophe.”
Warming of the climate is only a “catastrophe” in the wet dreams of Eco Nutters.
according to https://www.acer-acre.ca/resources/climate-change-in-context/the-past/impacts/impacts-on-lithosphere-land/glacial-periods-and-glaciers
“Over 20 glacial advances and retreats have occurred during the last 2 million years.”
So, clearly, there is no reason to think there won’t be another. Perhaps the slight warming occurring now will save us from a severe advance of the ice.
“The only “climate catastrophe” humanity will experience is the descent into the next ice age.”
That’s correct. There is definitely evidence for ice ages in history. There is no evidence for a runaway Greenhouse effect, even though CO2 levels have been much higher in the past than they are today.
Thank you again Dr. Roy.
It’s comforting to know that basic observations of everyday phenomena (e.g. cities are warmer than rural areas) by laymen such as me are simply explained by the formal scientific processes.
Hi, I live i the Las Vegas Valley,
The Official Weather station at the reid Airport is about 100-150 feet from a Major Street.
I can post pictures if wanted.
Tom
Trags, we’d love to see those pics, providing there is no personal or legal risk to yourself obtaining those pictures.
I recommend upload the pics to flickr or public facebook images or your favourite social share, make sure they are publicly viewable, then use “Submit Story” to send the link. If you want to write about how the temperature at the station compares to other parts of town, maybe dig up some historic pics, provide some background on any local green propaganda, take a picture of yourself photographing the station, lets see if we can put it together into an article.
I’ll ask Anthony and Charles to keep an eye out for your pics.
Something else I didn’t convey. The station looks like it is on a large bed of gravel. I will go by there tomorrow and take a few pics. Somewhere I have a satellite pic of the site also.
Hubbard and Lin did a study around 2002 that showed that the microclimates at measuring stations are sufficiently different that adjustments to temperature readings have to be done on a station by station basis. Your description of the microclimate at the LV airport is a prime example of this.
Maybe they should replace the gravel with an array of mirrors that would focus the reflected sunlight right at the temperature reading equipment.
Then they can tell us how “it’s worse than we thought.” 😉
I wonder who the heck was down-voting your comments and Eric’s?! What could possibly be wrong with doing some citizen science??
I can make a pretty good guess!
I was not able to get pictures from the fence as there are big signs prohibiting Pedestrians from crossing the street. So here is the Google Earth pic and a picture I took from the South side of Sunset Rd (looking North). I will see if I can get a better view of the ground around the station from a truck with someone else driving.
Tom
sorry I thought I could post 2 pictures.
Here is the Google Earth Pic.
A while back I did some work for a GeolSoc presentation. I was forward modelling glacial retreat data and tested temperature profiles from:
HadCRUT
CMIP5 & CMIP6 mean models
A linear trend + sinewave
The latter fits much better, with SD of residuals about half of the others.
However, I also noticed that if I add a linear warming trend of -0.08 degC/decade from 1960 onwards to HadCRUT4 (ie reduce the warming by that trend post-1960) I get a much better fit, almost as good as the linear trend + sinewave.
So my modelling would support reducing the warming trend in the surface temperature record to better fit glacial retreat observations.
There are government installations closer to Las Vegas than Winnemucca that might share weather data.
I the oval in the diagram, where Las Vegas is cooler, shows the difference in thermal conductivity Dr. Spencer mentions. Sand and loose soil heat up more quickly and radiate accordingly. Concrete has more “mass in the game”, so to speak and so heats more slowly, but by late afternoon both substances have reached their peak temperatures.
Typo….scratch the I, capitalize the T.