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Discussion > What's The Difference Between Measured UHI and Met Office weather forecasts

To the West of London and Heathrow are reservoirs and gravel pits along the Thames Valley and M4 Motorway. Heathrow Airport was built after WW2. So were some or all the gravel pits, M4 and M25. I do not know the timing of the Staines Reservoirs. Water is good at buffering temperature change. Tarmac is not.

Irrespective of any differences in solar gain and UHI, the amount of petrol and diesel burned on that section of the M4 and M25 must be huge. The M4 was built in the 60s/70s, and M25 later but has been widened since with more traffic and tarmac.

Should we now assume the M4 and M25 preheat air before it reaches the UHI of Heathrow? Staines Reservoirs are relevent because of ......?

Nov 3, 2016 at 3:21 PM | Unregistered Commentergolf charlie

golfCharlie.
I think it must be that some missing heat lies in their depths and when it emerges....!

Nov 3, 2016 at 4:09 PM | Unregistered CommenterACK

ACK, is it large carp burping methane and lighting it? With Eton College not too far away, you never know what frightful habits might have been acquired from the elite.

Nov 3, 2016 at 4:40 PM | Unregistered Commentergolf charlie

Victor Venema

Thank you for finding your way here, and for commenting. However, I must take issue with this:

"You find it so counter intuitive that it is not ever worth studying?"

If you read the whole thread, you will see that although I am not a scientist and have limited spare time, I am trying to study the subject to the best of my ability. I have made a number of points on this thread other than just with regard to airports. By the way, I wouldn't be surprised if Heathrow was warmer than the centre of London. It shouldn't surprise you, either, given the size of the airport, the amount of fuel burned there, and the extent of the concrete, runways, etc.

Petersen's paper contains this in its summary:

"Contrary to generally accepted wisdom, no statistically significant impact of urbanization could be found in annual temperatures. It is postulated that this is due to micro- and local-scale impacts dominating over the mesoscale urban heat island. Industrial sections of towns may well be significantly warmer than rural sites, but urban meteorological observations are more likely to be made within park cool islands than industrial regions." Do you agree? Where's the consistency?

Nov 3, 2016 at 7:26 PM | Unregistered CommenterMark Hodgson

Mark Hodgson, this is what you wrote on page 1 at Oct 20, 2016 at 8:21 PM:
"No worries, and I appreciate the link to Victor Venema's blog. I accept that he is the guru of homogenisation etc, and I will read the link carefully. However, having got this far, I'm already struggling to take it all too seriously:

"The best known inhomogeneity is the urban heat island effect. The temperature in cities can be warmer than in the surrounding country side, especially at night. Thus as cities grow, one may expect that temperatures measured in cities become higher. On the other hand, with the advent of aviation, many meteorological offices and thus their stations have often been relocated from cities to nearby, typically cooler, airports (Trewin, 2010). It would be worth studying which of these two effects are strongest for urban stations. My European colleagues expect it is the cooling due to the relocation to airports."

"cooling due to relocation to airports" indeed. In the UK we seem to have heat records reported regularly at Heathrow. The idea that airports are cooler (and presumably should see their temperatures adjusted upwards?) isn't one I can take terribly seriously, and I'm surprised Victor can write this apparently with a straight face."

So if you also find it worth studying, then we agree. But then I wonder why you write that have such a hard time taking me all too seriously and why you are surprised that I write that with a straight face. Still happy we agree.

Nov 3, 2016 at 9:15 PM | Unregistered CommenterVictor Venema

Victor Venema, you wish to quote previous comments so...

You wrote favourably about Gergis et al 2016 on aTTP's blog, and were contemptuous of those who queried the maths.

Has your maths improved?

Mine is just as bad but I never claimed otherwise.

Nov 3, 2016 at 10:28 PM | Unregistered Commentergolf charlie

https://andthentheresphysics.wordpress.com/2016/07/13/gergis/

Nov 3, 2016 at 11:06 PM | Unregistered Commentergolf charlie

Victor Venema

You seem to have side-stepped my last question. Would you like to answer it? I am genuinely interested in your opinion, I am keen to keep things polite, and I wish to learn. Can you enlighten me, please?

Nov 4, 2016 at 8:22 AM | Unregistered CommenterMark Hodgson

Victor Venema
I'd like to echo Mark Hodgson's Nov 4, 2016 at 8:22 AM posting.

My problem was, and still is that any urbanised location, which includes airports, will having a overall warming compared to the same location in a virgin rural condition , is that correct? The warming is nothing to do with GHG but due mainly to the urbanisation itself, is that correct? When measuring the effect of GHG as opposed to building of cities then one must remove the effect of the UHI first -is that correct? In order to remove the UHI one must compare the pristine rural location with its current urbanised condition - is that correct? As that is not possible in most cases the next best thing is to compare the urbanised (including airports) location with a (virgin) rural nearby - is that correct? The weather forecasts as given by the BBC say that city centre to pristine rural can be "more than several degrees" - are they correct? So what is the actual difference in the measured temperature of an urban area and its virgin rural predecessor?

Nov 4, 2016 at 9:01 AM | Unregistered CommenterSandyS

Mark is incredulous of Victor's assertion that temperatures at airports are generally cooler than those measured in town and city centres and gives Heathrow as a single counterexample. But if one takes the trouble to read the reference Victor supplies it gives the context:

The potential for a large-scale bias exists, however, if there is a widespread pattern of a particular type of site relocation in an individual country or region. A possible example of this is the establishment of many observing stations at airports during and after the Second World War, as aviation (and the influence of weather information on aviation) grew in importance. If these airport sites generally replaced town center sites, as occurred in some countries,[49] this would be expected to cause a general negative bias in mean minimum temperatures.

So, Trewin is highlighting a potential bias over the whole length of the instrumental record. If one then follows his ref 49, it is to a paper discussing an Australian surface station dataset, which has this

Many changes were identified over the period of record covered by the long term dataset. Changes identified in the station documentation included changes in instrumentation (such as the introduction of the Stevenson screen, usually around the turn of the century), in location (especially away from built up areas to airports, often around the middle of the century), in observer habits and in the environment (such as vegetation growth and urbanisation).

So a slight case of comparing different things, on the one hand the present-day example of the 6th busiest airport in the world (though when the wind is in the West or the South West it will be bathed in air that has passed over substantial bodies of water, not something that happens much in Central London), on the other the historical trend, over decades, for stations to move out from urban centers to airports away from or at the edge of cities. With evidence.

Definitely worth investigating further.

Industrialisation is not the same as urbanisation, of course.

Nov 4, 2016 at 9:40 AM | Unregistered CommenterPhil Clarke

SandyS,

This is why climatologists generally use anomalies rather than absolute temperatures. An anomaly is calculated by computing the average temperature at a station over a given baseline period, and then expressing the temperature as the difference, or anomaly, from that baseline. This removes difference due to siting, elevation etc.

So an urban station might have an average temperature of say, 10C, a rural one 7C, if on a particular day, they record temperatures of 11C and 8C, they will both have the same anomaly, of 1C. Similarly if they both experience the same warming trend the anomaly will record this.

The UHI issue is that some sites over time become more builtup, introducing a spurious warming into the trend, which must be removed (just as with other biases such as instrumentation changes or observation practices). Studies (see previous references) have shown that the effect is small, on a global scale and the techniques used to remove it work well.

Nov 4, 2016 at 9:52 AM | Unregistered CommenterPhil Clarke

Phil Clarke
My point is that, in your example, when compared to the virgin rural site which is now industrialised or urbanised* the anomalies are in fact 4'C and 1'C. In order to calculate the GHG effect the 4'C anomaly is made up of at least 3'C due to UHI.

* In terms of UHI versus virgin rural both have a heating effect.

Nov 4, 2016 at 12:31 PM | Unregistered CommenterSandyS

Phil Clarke
By

the techniques used to remove it work well.

Do you mean they match the models based on little or no UHI?

If so then the increases in 20th century temperatures still have the UHI 3'C anomaly built into them. Global population having grown from 1.6 billion to 7 billion during the 20th century coupled with rural depopulation means most weather stations in use throughout the 20th century will have gone from virgin rural to urban or industrial (if you want to consider them differently). The UK population doubled during the 20th century with similar moves to the cities.

Nov 4, 2016 at 12:44 PM | Unregistered CommenterSandyS

Phil Clarke, when the wind is blowing from the west and south west across Heathrow Airport it is blowing across the M4 and M25 plus numerous other busy roads. Don't you think that counters your arguments about Staines Reservoirs?

The Reservoirs, Thames and other gravel pits will also cause some warming in cold weather which will raise lower temperatures therefore boosting average temperatures and UHI.

I think your Red Herring has been smoked.

Nov 4, 2016 at 1:01 PM | Unregistered Commentergolf charlie

I was very glad that Victor Venema found his way here and sought to engage in discussion. I'm sorry he's disappeared, just when we were winding up to ask him questions. I, for one, do not seek to trip him up, but instead to have some genuine discussion with someone who really should be able to help us with our curiosity on this thread.

Maybe he'll return when he's less busy. I hope so.

Nov 5, 2016 at 8:28 AM | Unregistered CommenterMark Hodgson

Mark Hodgson
+1

Nov 5, 2016 at 9:07 AM | Unregistered CommenterSandyS

This paper in Physics Today has been linked in WUWT today.


Land’s complex role in climate change
Roger A. Pielke Sr, Rezaul Mahmood and Clive McAlpine

Excerpt:

To date, most reporting on climate has focused on the possibility of catastrophic warming due to carbon dioxide and other greenhouse gases released into the atmosphere. The assessment of climate change risk has essentially been distilled to a single metric: the global average surface temperature. That reality was evident at the 2015 United Nations Climate Change Conference in Paris, where the central negotiating point was whether the global temperature rise should be limited to 1.5 °C or 2 °C. Indeed, a 2016 opinion piece by Simon Lewis (University College London and the University of Leeds, UK) states that, “by endorsing a limit of 1.5 °C, the [Paris] climate negotiations have effectively defined what society considers dangerous.”1

I'll try and read it over the next couple of weeks.

Nov 8, 2016 at 7:32 PM | Unregistered CommenterSandyS

Sandy S

Thanks, but the link didn't work - for me, at least. Could you try again, please?

Thanks.

Nov 8, 2016 at 7:47 PM | Unregistered CommenterMark Hodgson

Mark Hodgson
In WUWT today
https://wattsupwiththat.com/2016/11/18/study-uhi-in-hong-kong-accounts-for-most-warming-since-1970/

“The seasonal unit root test makes it possible to determine the stochastic trend of monthly temperatures using an autoregressive model,” says Prof. Wai Ming To. “We found that Hong Kong’s urban mean air temperature has increased by 0.169°C per 10 years over the past four decades using monthly temperature data, or 0.174°C per 10 years using annual temperature data, and the trend is likely to persist.”

Sorry I missed the fact the other link didn't work, the link is

http://scitation.aip.org/content/aip/magazine/physicstoday/article/69/11/10.1063/PT.3.3364

Nov 19, 2016 at 9:23 AM | Unregistered CommenterSandyS

Sandy S

Many thanks - looks interesting. I will read in more detail over the next few days.

Nov 19, 2016 at 3:03 PM | Unregistered CommenterMark Hodgson