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.