By Paul Homewood
I ran a post the other day on daily record temperatures in the Southeast of the USA.
Just to recap:
A record daily high means that temperatures were warmer on a given day than on that same date throughout a weather station’s history.
In other words, it does NOT include records set, but subsequently beaten. Also note that subsequent ties are included.
My exercise showed that, in the last decade, across rural stations there were more new daily low records than highs, but at urban stations, the opposite was true. This seemed to be clearcut evidence of UHI effect.
For my selection of rural sites, I used population data on the GISS database, (itself sourced from GHCN), which classifies all sites with less than 10,000 as rural. As I pointed out at the time, this still left small towns in the rural category, and I therefore suspected I was underestimating the UHI effect.
Steven Mosher correctly points out that the GISS data is, at best, crude, and Ronan Connolly suggested I also use the “brightness index” that GISS use to indicate whether a site is truly rural. This is based on satellite data, and allocates three categories – “A” for dark, “B” for dim, and “C” for bright.
So, from the original 18 stations I had identified as rural, using the brightness index, I have filtered the list down to seven sites. While this is a small number, they are well spread geographically:
Highland Home –AL
Lincoln – VA
Highlands – NC
Little Mountain – SC
Santuck – SC
Yemassee – SC
Lake City – FL See Update
The results are startling. The ratio of highs to lows, at rural stations in the last decade, is 0.47, but at non rural sites, the ratio is 1.51. It is clear evidence that the UHI effect is keeping night time temperatures higher.
http://cdiac.ornl.gov/climate/temp/us_recordtemps/ui.html
As the table below makes clear, the big difference between rural and urban is in night time lows, rather than daytime highs.
| 2001-10 | Decadal Average
1911 to 2010 |
% of
Average |
|
| Record Highs | |||
| Urban | 1031 | 1441 | 72 |
| Rural | 191 | 332 | 58 |
| Total | 1222 | 1773 | 69 |
| Record Lows | |||
| Urban | 685 | 1299 | 53 |
| Rural | 409 | 305 | 134 |
| Total | 1094 | 1604 | 68 |
Trends
These are only daily records, so do they tell us anything about overall temperature trends? Well, CDIAC certainly think they do.In their introduction of the new interface, from which my data is drawn, they have this to say:
Changes through time in record high and low temperatures (extremes) are also an important manifestation of climate change (Sect. 3.8 in Trenberth et al. 2007; Peterson et al. 2008; Peterson et al. 2012). Meehl et al. (2009) found that currently, about twice as many high temperature records are being set as low temperature records over the conterminous U.S. (lower 48 states) as a whole. As the climate warms further, this ratio is expected to multiply, mainly because when the whole temperature distribution for a location or region shifts, it changes the “tails” of the distribution (in the case of warming this means fewer extreme cold temperatures and more extreme hot temperatures.
And back in 2009, NCAR’s news release on Gerald Meehl’s paper on daily record temperatures stated:
Spurred by a warming climate, daily record high temperatures occurred twice as often as record lows over the last decade across the continental United States, new research shows. The ratio of record highs to lows is likely to increase dramatically in coming decades if emissions of greenhouse gases continue to climb.
“Climate change is making itself felt in terms of day-to-day weather in the United States,” says Gerald Meehl, the lead author and a senior scientist at the National Center for Atmospheric Research (NCAR). “The ways these records are being broken show how our climate is already shifting.
Significantly, NCAR also go on to say:
The study also found that the two-to-one ratio across the country as a whole could be attributed more to a comparatively small number of record lows than to a large number of record highs. This indicates that much of the nation’s warming is occurring at night, when temperatures are dipping less often to record lows. This finding is consistent with years of climate model research showing that higher overnight lows should be expected with climate change
The evidence, at least as far as the Southeast is concerned, is that the small number of record lows is a result of UHI, and not climate change.
UPDATE
As Latitude points out, Lake City, FL is wrongly categorised as <10000 by GISS. Taking this out of the equation brings the warm to cold ratio for rural sites down slightly to 0.45.
As in voting, where it’s not who votes but who counts the vote that matters, in climate science what matters is who collates and interprets the data.
This is such a simple and sensible way of looking at the problem, if indeed there is a problem. Thank you, Paul Homewood.
And every meteorologist is familiar with the UHE. But Warmists seem mysteriously oblivious.
Agree with all the evidence cited here (how could one not?) but this is simply preaching to the converted, as with Anthony’s own stations project. To the warmists this is just denialism, end of story.
Nice work Paul.
http://youtu.be/t-sXHl3l-rM
I’ve seen the snow each winter 6 feet deep. My granddad was only 4 foot 9 inches. We never saw him from December until march.
“This indicates that much of the nation’s warming is occurring at night, when temperatures are dipping less often to record lows. This finding is consistent with years of climate model research showing that higher overnight lows should be expected with climate change”
I’m not sure about that claim, but I do know that the effect of a nearby heat sink will produce exactly those results – the heat sink radiates its heat most actively when the surrounding temps dip
significantly below the temp of the sink (typically at night), as opposed to during the day when surounding temps are close to those of the heat sink. If the temps are the same, the heat sink won’t radiate at all.
“This finding is consistent with years of climate model research showing that higher overnight lows should be expected with climate change”
Thousands of such linear thinkers would never in a thousand years make the discoveries of any scientists whom we know from history. None of the present mechanically educated lot in the ‘consensus’ will find himself in the list when the present era turns into history. No Stefan-Boltzmanns, Planck’s, Lavoisiers, etc. This will merely be part of an era cited when, with the final straw, it became necessary to make a huge overhaul in basic education and higher learning. Shameful, heart rending, embarrassing when we have to decide who is a real scientist by how much abuse has been hurled at him.
Anthony, maybe some of this could make its way into your stations paper.
Excellent post Paul.
I live in the Phoenix, Arizona area – southeast of metropolitan Phoenix a couple of miles north of city’s edge, which is distinct due to land-use rules and Indian reservations. I have measured UHI many times and during summer it is between 5 and 7 degrees F. Not trivial. Also, there is a delta humidity with the urban area being less humid.
Are there any readers of this blog from the Southeastern US who have measured their local UHI? It is easy to do. Buy a temperature logger from this site. Attach it to you car aerial. At just about sundown, drive from a fully developed urban area, to a sparsely populated, preferably rural area at the same elevation. Drive back. Plot data.
It’s easy and fun – I usually take the dogs – they love the ride!
Well, even with heat islands and poorly placed stations I came across this on Y! news (probably the worst source of news I usually read, but interesting in this case, none the less). The article, obviously, blames AGW, but funny enough, discredits it (a first). [source 1=”http://ca.news.yahoo.com/the-winter-that-ruined-everything-203709683.html” language=”:”][/source]
Worst Winter ever
Calgary: With 52.4 cm of snow, it was Calgary’s snowiest December since 1924, when 56.9 cm fell. In November, Red Deer broke records dating back a century, receiving a whopping 62.5 cm of snow.
North Battleford: The city hit 9.3° C on Jan. 15, the warmest January temperature ever recorded
Burwash: On Jan. 24, it reached 16.5° C, the warmest January temperature ever recorded in the Yukon
Winnipeg: Since record-keeping began in 1938, this was the city’s second-coldest winter ever
Yorkton: On Jan. 15, wind gusts reached 117 km/h, the strongest gusts ever recorded for January
Kenora: The city experienced its coldest winter on record
Great Lakes: As of March 7, 92.2 per cent of the Great Lakes were covered in ice—their second-highest level of ice coverage since record-keeping began. The record remains February 1979, when 94.7 per cent were covered in ice.
Hamilton: The city set a record low on Jan. 7, hitting -24° C (-41° with the wind chill)
Ottawa: The capital was colder and snowier than average in December, January and February
Charlottetown: P.E.I.’s capital got 300 cm of snow from December to February, a 52 per cent increase from normal levels
Stephenville: With spring around the corner, the town has more than two metres of snow still on the ground
Toronto: It was the city’s coldest winter in 20 years, and the most snowbound on record (days with at least one centimetre of snow on the ground). The previous record was 81 days; as of March 7, Toronto was at 89 days.
Sorry, source: http://ca.news.yahoo.com/the-winter-that-ruined-everything-203709683.html
Lake City – FL
population 1850 – ~7500
population 2014 – more than 70,000
Funny how during the late 60’s and early 70’s when we had the cooling scare, thermal mass was understood to be a good thing to try and get some extra warmth for homes etc.
Is the new low-temperature always a night-temperature? I don’t have any data to disprove or approve, but I can’t imagine. At least You should drop a word or two in your text upon this topic?
The impact of ‘brightness’ has another factor too.
I don’t know the situation elsewhere, but in the UK it is becoming increasingly common for alternate streetlights to be switched off. Whole sections of streetlights are switched off overnight (…) in places too. Obviously this is described as saving on CO2 emissions, but costs for local authorities are probably as big a reason.
Where this may be introducing a further warm bias in the GISS temperature index is that, while the Brightness value for an area with less street lighting may be lower than 10 years ago, its level of urban development probably is not, and may even have increased. However, GISS may well be making a smaller UHI adjustment than would have been the case ten years ago.
It would take a lot of investigation to quantify this, but it’s surely another new factor causing a warm bias in GISS’ index.
This is huge, especially if it applies to the entire US, and to the entire world.
Is this data just for the Southeast U.S.?
Do we have the data for the US as a whole and the world?
Having seen some of the examples from Anthony’s surface stations, I’d guess that a large proportion of the uhi comes from the initial urbanisation. If this is so, how long would it be before we would expect to see the uhi effect drop out of the calculation?
Recently the BBC weather forecasters (or sometimes people more accurately described as weather presenters) have been saying “These temperatures are for built-up areas. It may be several degrees colder in the countryside.”
“Significantly, NCAR also go on to say:
… This finding is consistent with years of climate model research showing that higher overnight lows should be expected with climate change”
Higher overnight lows are also, and more solidly, consistent with UHI, where all the added urban concrete releases the daytime heat longer into the night.
Strike
Is the new low-temperature always a night-temperature? I don’t have any data to disprove or approve, but I can’t imagine. At least You should drop a word or two in your text upon this topic?
Quite right, it does not have to be night time, simply the minimum. Night time tends to be used as an easily understood moniker!
It gets a bit complicated talking about “high daily minimums”, or “low daily maximums”.
Latitude
Lake City – FL
population 1850 – ~7500
population 2014 – more than 70,000
GISS still show as <10000.
Wiki show 12000, but as "Principal City of the Lake City Micropolitan Statistical Area", which has pop of 67000.
I guess it shows what Mosh was saying about GISS is right!
BTW – Lake City has a ratio of 0.75 warm to cold, so if I exclude this the ratio for rural drops even further to 0.45.
@Francisco
I confirm your collection from across Canada. It will be -20 C or colder tonight and tomorrow night in Waterloo, Southern Ontario and the wind chill will be about -30. We lost nearly 30 cm of snow cover to a sort of melting/consolidation in the past two days but it is still so high it is hard to see cars coming at most neighbourhood intersections in the city.
I didn’t heat about Kenora. What is the ice thickness around there?
[“Hear” about heating up Kenora? 8<) Mod]
@Gary Young Pearse says:
“Thousands of such linear thinkers would never in a thousand years make the discoveries of any scientists whom we know from history. None of the present mechanically educated lot in the ‘consensus’ will find himself in the list when the present era turns into history.”
Well, that highlights the difference between schooling and education.
Keith says:
March 16, 2014 at 11:01 am
The impact of ‘brightness’ has another factor too.
I don’t know the situation elsewhere, but in the UK it is becoming increasingly common for alternate streetlights to be switched off. Whole sections of streetlights are switched off overnight (…) in places too. Obviously this is described as saving on CO2 emissions, but costs for local authorities are probably as big a reason.
——————-
That’s the result of government-imposed energy poverty kicking in. I hope you Brits can fix that.
Crispin, on the Wet Coast, the daffodils are up and I just grilled lunch on the deck in shirtsleeves. We did have some snow a few weeks ago, just in case anyone asks. Just a normal winter, not as bad as ’93 here.
gregole says:
March 16, 2014 at 9:43 am
Anthony will sell people the kit you need. I have two temperature loggers that are currently in a friend’s refrigerator. (And a voltage logger I’ve used to monitor the charge state on the supercaps on Davis’ solar powered weather station.)
http://wattsupwiththat.com/2010/04/04/measure-uhi-in-your-town-with-this-easy-to-use-temperature-datalogger-kit/
Remember this study? Significant UHI in China.
http://wattsupwiththat.com/2011/07/28/new-paper-uhi-alive-and-well-in-china/
“The UHI trends are 0.398°C and 0.26°C decade−1.”
“Off Topic”, but I see that “The Day After Tomorrow” is popping up again on the TV schedules here in the US. (The movie’s basic premise was that it’s cold because of Global Warming.)
I wonder if this winter’s “polar vortexes” had anything to do with the scheduling?
A carefully chose seven representatives rural settings, er, make that six actual rural settings and one urban interloper.
That makes for a 14.3% error rate. Potentially throughout GISS; well, given the crusader almost a gavin. heh.
” This indicates that much of the nation’s warming is occurring at night”,
Okay, I will bite.
How does the something warm at night when the sun is not present and the net energy flow is away from the ground straight through the atmosphere and into space.
You can can cool something (remove energy) and at the same time warm it.
If the sun is not present, and warmer air is not being moved into an area that is relatively cooler, warming can not occur!
This guy works at NCAR?
Embarrassing to say the least!
He opened his mouth and has shown the world has stupid and ignorant he is. The universities that ‘awarded’ him degrees need to pull them back.
Wrong, what he said was just plain wrong.
Gunga Din says:
March 16, 2014 at 3:48 pm
The film was supposed to inspire a national dialog on global warming. Instead
the scientifically literate laughed at it, and others went on to the next movie.
This fool wrote a web page to get ahead of the discussion, probably not worth the effort, but I learned some useful stuff. http://wermenh.com/2016.html – “2016: The [Next] Year without a Summer – Notes on Abrupt Climate change”
The movie’s science advisor was listed as “Michael Molitor” who seems to have kept a low profile ever since. He seems to be at The Climate Change Research Centre at USNW, see http://www.ccrc.unsw.edu.au/staff/adjunct.html (his photo has the movie marquee behind it), and his blurb:
Many of us with retired parents know that Lake City Florida is a big place now (think The Villages). 😉
At last count, there were about 250k senior folks down there (they have an age requirement of at least 35, no children).
Really dumb question here. Regarding the Tmax and Tmin measurements; does it matter how long it takes to reach those temps? Or how long the temps remain close to those highs/lows? Is rate of daily temperature change studied at all, or does it have any meaning in the overall context of climate change?
@paul
Is there time-stamped intraday temperature data that will allow you break urban area daily highs into new highs set during the day and new highs set during the night?
Is there an official NOAA stance on UHI in plainly worded English? I tried looking for it once, but I recall that I felt like I was drowning in bullshit and started thinking, “Wait, they want me to believe that going from 390 to 410 parts per million of CO2 is catastrophic, but somehow paving over ~10% of the U.S. doesn’t affect temperatures?” Maybe I misunderstood. If the warmists have a clearly worded summary of their stance on UHI, please provide a URL because I’d like to understand their position.
Curious as to the density of weather stations in our vast very rural expanses out West. Seems to me the data needs to be from evenly spaced sources, even when no one lives there. No sense in having ten stations in every city in the East when there aren’t any cities within hundreds of miles where I live. It seems they are collecting more temperature data points in heavily populated areas, like national voting in large red states with fewer people versus packed blue states with more votes. Rural areas are just underrepresented.
The part that is missing in the discussion of record this and record that is the underlying physics of the surface energy transfer. There are 3 different temperatures that are important, and only two are recorded in the historical weather station record.
The surface temperature is exactly that: the surface temperature on the ground under the weather station. The weather station records the air temperature measured in a ventilated enclosure located at eye level 1.5 to 2 m above the ground. Historically, only the maximum and minimum temperatures were recorded using Six’s thermometer. (Some countries used different methods)
The surface temperature is determined by the short term (nominal hourly) surface flux balance. The ground is heated by the absorbed solar flux and cooled by a combination of net LWIR emission, sensible heat (dry convection) and evaporation. In addition, the surface thermal gradient heats the subsurface layers during the day and they return the heat to the surface in the evening. None of these terms can be separated out and averaged individually. The change in surface temperature is the change in heat content (enthalpy) divided by the effective heat capacity of the surface layer.
During the day, the solar heated surface is warmer than the air above. The heat flow follows the thermal gradients. The cooling involves a combination of net LWIR emission and moist convection. At some point in the evening, the surface and air temperatures equalize and the moist convection essentially stops. Cooling is now through net LWIR emission only. The downward LIWR flux from the atmosphere originates from within the first 2 km layer of the troposphere. Typical values are 50±50 W m^-2. Low humidity increases the net LWIR flux and low cloud base thermal emission ‘closes’ the LWIR window.
The surface now acts as a ‘heat pump’ and ‘pulls’ the heat from the surface air layer and radiates it to space.
The minimum MSAT is in general a measure of the base temperature of the air mass of the local weather system as it is passing through. This is modified by the local microclimate, particularly things like ‘cold air drainage’. In many regions, the prevailing weather systems are formed over the oceans and any long term trend in the minimum MSAT follows the relevant ocean surface temperature trends. In California, this is the Pacific Decadal Oscillation. In the UK it is the Atlantic Multidecadal Oscillation. The PDO and AMO can be used as climate ‘references’ to check the weather station minimum MSAT. In simple terms, to get started, the urban heat island effect is the difference in linear slope between the minimum MSAT trend and the relevant ocean trend over the same period of record. The devil of course is in the microclimate details.
The maximum MSAT is a measure of the convective mixing between the upward surface heated air and the cooler air above, as recorded by the MSAT thermometer. Under full summer sun illumination, a dry surface can easily reach 50 C or more. The maximum MSAT depends on the solar flux and the evaporation. Droughts and ‘blocking highs’ produce increased maximum MSATs.
The observed increase of 100 or so ppm in the atmospheric CO2 concentration has produced an increase in the downward atmospheric LWIR flux of approximately 1.5 W m^-2. When this increase is added to the short term flux balance and used to calculate the increase in surface temperature, the effect is too small to measure. The total change in the surface flux balance has to be divided by the heat capacity of the surface layer.
There can be no ‘CO2 signature’ in the weather station climate record. The climate models have been fraudulently ‘calibrated’ using ocean surface temperatures. [This is the source of the ‘pause’]. Over the oceans, the penetration depth of the LWIR flux into the surface is less than 100 microns. Here the increase in LWIR flux from CO2 is coupled to the surface evaporation and dissipated as a minute part of the ocean surface cooling flux.
Instead of arguing over the MSAT record, please start to do some quantitative analysis. There are thermal engineering analysis programs that should be capable of calculating UHI.
References
Clark, R. Energy and Environment 24(3, 4) 319-340 (2013) ‘A dynamic coupled thermal reservoir approach to atmospheric energy transfer Part I: Concepts’
Clark, R. Energy and Environment 24(3, 4) 341-359 (2013) ‘A dynamic coupled thermal reservoir approach to atmospheric energy transfer Part II: Applications’
These unfortunately are pay walled. More info is available on my website at: http://venturaphotonics.com/GlobalWarming.html
Of the many ways to present climate data related to extremes, I find this quite useful.
http://www.geoffstuff.com/Melbourne%20very%20hot%20days%20curve.jpg
I’d be most interested in this type of analysis from other countries where, for example, the instrumentation had different historic ‘noise’ properties.
Excellent article and it confirms what all of us already know. We live 1.5 hours outside of a major urban centre and we have tracked the delta in temperature from 4 to 7 C from our place to the UH sink. Indeed even in our rural location you can put 2 stations 2 miles apart and register temps 2-3 C different or higher, on any given day. As often-stated, there is no globaloney-anything, just the interplay of physical thermodynamics, regional variations and globalized factors such as sun irradiation.
HWR says:
March 16, 2014 at 6:54 pm
NOAA NCDC currently claim that their Menne & Williams, 2009 data “homogenization” method is able to “remove” all the non-climatic biases from their station records, including urbanization bias – see here. Because they use the homogeneity-adjusted versions of their station records for their global temperature trend estimates, they assume that their “global warming” estimates are unaffected by UHI.
However, in our “Urbanization bias III. Estimating the extent of bias in the Historical Climatology Network datasets” article (which we have submitted for open peer review on our Open Peer Review Journal forum), we find that this claim is invalid (see Section 4.3 in particular).
Keith says:
March 16, 2014 at 11:01 am
Moderators: I forgot to close the quote tag in the last comment. Can you delete the last comment and leave this version instead?
Keith says:
March 16, 2014 at 11:01 am
A couple of points, which don’t disagree with what you’re saying, but provide some relevant information:
1. The brightness values Paul is using are the ones from the NOAA NCDC GHCN metadata (“A”, “B”, “C”). The ones that GISS use for their actual adjustments come from a slightly different dataset – the Imhoff et al. NASA night brightness (“1”, “2”, “3”). The two datasets are fairly similar though, so this is just a technicality.
2. Both of these night brightness datasets were compiled in the 1990s. I forget the exact details for the GHCN brightness metadata, but as far as I remember the NASA values were determined from a 6 month period of satellite analysis from late 1994 to early 1995.
3. The night-brightness to urban development ratio varies quite widely from country to country, e.g., the U.S. has one of the highest per capita electricity usages, while many of the developing countries have very low per capita usage, even though their urban metropolises have quite substantial UHIs. So, if you rely solely on the night-brightness data for a global analysis, you quickly start getting serious errors. This is why we recommend using more than one “urbanization metric”, e.g., population and night brightness
However, in Paul’s analysis, he is just focusing on a region of the U.S. The night brightness:population ratio for the U.S. is very well calibrated (the U.S. have decadal census data going back to the 1700s!), so as long as Paul is just limiting his analysis to the U.S. it should be fine.
We discuss some of the serious problems with GISS’ usage of their night brightness dataset in our “Urbanization bias II. An assessment of the NASA GISS urbanization adjustment method” article (which we have submitted for open peer review on our Open Peer Review Journal forum) (see Sections 4.2 and 4.3 in particular).
Has anyone downloaded the temperature data from the USCRN and posted it? The system has been fully operational since 2008 and it should show an unbiased temperature history for the recent time period.
Roy Clark says:
March 17, 2014 at 12:24 am
“..
The surface temperature is determined by the short term (nominal hourly) surface flux balance. The ground is heated by the absorbed solar flux and cooled by a combination of net LWIR emission, sensible heat (dry convection) and evaporation. In addition, the surface thermal gradient heats the subsurface layers during the day and they return the heat to the surface in the evening. None of these terms can be separated out and averaged individually. The change in surface temperature is the change in heat content (enthalpy) divided by the effective heat capacity of the surface layer.
…”
Oh dear here we go again – energy flowing from low areas of energy to high areas of energy..
Something that is 60 Degree F (Air) can not ‘heat’ something that is 70 degrees F (dirt)…..
Energy flow into the surface of the earth from the sun and then the energy is transferred back into space. The only thingie that can vary is the rate….
Roy Clark
Ocean holds 95% of earth surface heat. Atmosphere is < 1%. But we live on land and weather happens in the troposphere so measure air temperature.
"Over the oceans, the penetration depth of the LWIR flux into the surface is less than 100 microns. Here the increase in LWIR flux from CO2 is coupled to the surface evaporation and dissipated as a minute part of the ocean surface cooling flux."
If all 324 W/m^2 of "back radiation" is cancelled by evaporation, the ocean will radiate about 200 W/m^2 to balance incoming solar. Its temperature would be -29 C. The ocean will freeze. Only a small portion is evaporated, the rest is absorbed and re-emitted by seawater.