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UAH reveals UrbAn Heat

UAH reveals UrbAn Heat16-12-2010 19:18
Frank Lansner
How UAH satellite temperature data supports Urban Heat (UHI) as a real and significant factor when estimating global temperatures.

NH temperatures in recent years:

Fig1. The black temperature graph - average RSS+UAH satellite NH (Land + Sea) - has a smaller warming trend than the other (brown) land data series – but in fact resembles the cooler Sea Surface Temperature trend.
(The blue graph "CSST" is an average of the rather similar SST´s: MOHSST6, HADSST1, HASSST2, ERSST.v3b, HADISST1and Kaplan SST 98.)

The satellite data represents both land and ocean temperatures – and yet they resemble only the blue SST´s. Why ?

Satellite temperatures and SST do have one thing in common: They are for sure without the UHI warming error from the cities and airports – they are Excl. UHI:

Fig2. Now we split the UAH data up in a land fraction and an ocean fraction. Both still seems to yield considerably lower temperature trends than the land data (brown) measured from mostly cities and airports on the ground.

So UAH land temperatures have colder temperature trend than the ground based land temperatures. Are the land-data deviations due to general issues with the satellite data then? Perhaps the satellite data happens to show colder trends for some "known" reasons etc?

Not likely: There is a good resemblance between the UAH ocean temperature trends and then the directly measured ocean data, SST ("CSST"). This shows that satellite data and thus also satellite land data are indeed useful and likely to be correct.

So, unless the satellites always starts to fail just when flying over land, the deviation between land data measured on the ground (mostly from cities and airports) vs. satellite land data is likely to originate mostly from the ground based measurements. This "extra heat trend" seen in the ground based land temperature data may be explained by UHI + possibly faulty adjustments of data and siting problems.

In fact, one more result might also support the correctness of UAH data:

Systems will always seek equilibrium.
On fig 2 we see a pattern of gabs between the UAH land and ocean data. However, after the gabs the UAH land and ocean data these data unite again and thus despite the temporary deviations, they still seem to produce a common trend.

Is it surprising that the temperatures over land and sea will seek equilibrium? Or would it rather be surprising if they did not? What force should maintain a still bigger difference in temperatures between land and see trends?

Fig 3. Lets focus on the temporary gabs between satellite land and ocean temperatures. The green curve represents a de-trended version, just the difference between the land and ocean temperature data from satellite. From fig 3 it appears to some degree that land and sea temperatures align or reaches equilibrium mostly when temperature do not change fast.

Lets take a look at the same phenomenon in the decades just before the satellite age – I use original temperature data published en around 1974-84 for this:

Fig 4. On this illustration we have confirmed, that the land-AIR temperatures are fastet to reach a temperature change "100%", then the Marine-AIR temperatures comes soon after "80%" and finally the sea water surface temperatures reaches the new temperature level. Again it seems, that after a given time ocean temeperatures and land temperatures tends to find equilibrium.

With a reasonable argumentation that also the Land fraction of satellite data is useful, lets look at the "extra heat" seen in the ground based land temperature measurements (mostly from cities and airports). How much "extra heat" do the ground based land data contain?

Fig5. The extra heat in CRUTEM3 land data compared to UAH on NH is 0,103 K per decade.

Fig6. On global scale, the extra heat in CRUTEM3 land data compared to UAH on NH is 0,088 K per decade. (0,23K over 26 years from 1981 to 2007).

If the extra heat in data measured on land is applied to a period 1900-2010 – just to get a rough idea of the possible impact - using 35-40% land area as hadcrut does - we get global extra heat of + 0,34 - 0,39 K to the overall warming of the Earth related to the extra heat occurring when measuring from cities, Airports etc.

0,34-0,39 K is roughly half the supposed global warming 1900 – 2010 , but in this context we cannot claim to have quantitative precision, obviously. But the rough estimate of 0,34-0,39 K does suggest that the impact of "extra heat" that cannot be detected by satellites plays an important role when trying to estimate global temperature trends.

The problem of "extra heat" in land temperatures (likely to be UHI and more) is escalated by GISS because they extrapolate the ground based land temperature measurements over the oceans in stead of using real ocean data:

Fig7. In the case of Hadcrut temperature series they use around 35-40% land data when calculating global data, but GISS have a temperature product using roughly twice this fraction for land area as fig 7 shows.

Fig 8 until around 2008 this illustration of land vs ocean temperatures was online at the NASA/GISS website. As we have seen, satellite data indicates that land temperatures from ground has trend around twice the trend of land data from satellite data - and as almost twice the warming trend of SST, ocean data. This tendency is confirmed on fig 8. From 1880 to 2007 we have an ocean warming trend around 0,6K and for land its around 1,2 K - twice.

Again, we saw from 30 years of satellite temperatures that global satellite data matches ocean temperatures rather closely. If valid, then the fig 8 indicates a 0,6 K faulty extra heat, UHI etc from 1880 to 2007.


Article from which most graphics where taken:
Review and feedback of the above article by E.M.Smith, Musings from the Chiefio:
"The rewritten past":
17-12-2010 17:47
Bo Vinther
Dear Frank

Good to see that you have already made it to, and thank you for the above analysis.

Let me just add that if you use RSS satellite temperature data, instead of the UAH satellite temperature data, then you get somewhat different results (see below figure).

In the RSS data, land temperatures increase ~40% quicker than ocean temperatures, and the trend in RSS land temperatures is only ~10% smaller than in CRUTEM3 (i.e. surface land) temperatures. This does not leave much room for a significant UHI problem in CRUTEM3.

Calculating the global land temperature trends for the 5 different data sets covering the period 1979-2010 I get the following:

GISS (surf. obs.): 0.20 K/decade
CRUTEM3 (surf. obs.): 0.22 K/decade
NCDC (surf. obs.): 0.29 K/decade
RSS (sat. obs.): 0.20 K/decade
UAH (sat. obs.): 0.18 K/decade

Hence to me it looks like that it's only the NCDC land data that might have a problem.
The GISS, CRUTEM3, RSS and UAH observations all agree on the same trend within 10% (0.20 +/- 0.02) for global land areas. An agreement that I find impressive given the difference in observation techniques (satellite detection vs. surface thermometers).

Attached image:

18-12-2010 02:40
Frank Lansner
Dear Bo!

That i used UAH is infact pure coincidence.. and then you find that RSS behave differently ??? Thats odd. But thanks for impressing response!

1) I am very curious. Who/what/howcome did you start testing with RSS data - where ??? did that idea come from? Normally UAH and RSS are considdered rather alike? "who told you" :-)

2) As I argue in the article: In UAH data, every time there is some years with pause or a little reverse in temperatures for some years, the land data equals ocean data. They reach equilibirum.

Now, as a son of the DTU professor in thermodynamics, i HAVE to considder this important and there fore still, UAH appears best choice. or?

K.R. Frank
19-12-2010 04:07
Bo Vinther
Dear Frank

1) I looked at the RSS data, simply because you had done the analysis with UAH. No need to just repeat your work - that would be too boring....and I trust your calculations.

2) The equilibrium between land and ocean could change with incerasing greenhouse gas concentrations. One way could be that more greenhouse gasses over land means less radiation to space and thereby higher nighttime temperatures. Over the ocean the great heat capicity of the water means that nighttime temperatures can't drop very much no matter what, so there the effect of the greenhouse gas increase would be smaller.

I will, however, admit that UHI effects also yield higher nighttime temperatures, so it cannot be ruled out that some of the extra warming we are seeing in the surface observations from land areas are due to UHI problems.

Finally I would like to stress that even if the UAH data are correct (trend 0.18K/decade over land) then the UHI effect can only be responsible for ~20% of the trend in CRUTEM3 (trend 0.22 K/decade). Extrapolating this possible UHI effect to the whole period 1880-2007, would mean that 0.2-0.3K (not 0.6K as you write) of the 1.2K increase in temperature from 1880 to 2007 seen in CRUTEM3 could be due to UHI problems.

19-12-2010 17:05
Frank Lansner
Dear Bo!
Again-again im simply thrilled to read you answers. i can guarantee you, that if the "alarmistic" voice in general where of the Bo Winther type, the climate debate would be a very interesting scientific goldmine of exciting thoughts and perspectives.
If the "Alarmist" site was like you, then there would be no polarised trench fight but only truth seeking debate.

Now what you say is put Frankly: "Frank, the UAH numbers in fact also set a limit to how high UHI can be"

And of this I am aware, and I respect. Because, even though the UAH number might indicate more UHI than some scientist believe, it does seem that the UAH data also indicate a lower UHI than some sceptics believed.

When I worked with the article, i was therefore a minor revelation to me that at least the high-end estimates of UHI i myself have considdered possible to me now looks a little less likely.

I calculated around 0,108 K per decade "extra heat" on NH per decade (where extra-heat of the lad based temperatures could be UHi, adjustments and siting issues).
So far i have not diged too much into the SH and global numbers, but for now the global CRUTEM vs UAH globally diference (from land numbers) is perhaps more like 0,06K/decade "extra heat" in the global.

And this number appears to set an upper limit to what UHI, adjustmenst and siting problems combined can be.
The heating from the 1940 peak to present peak is often referred to as being around 0,5 K. And with a "max" for artificial errors on perhaos the 0,06 K per decade, even if UAH is THE correct dataset, this wont make the 1940 as hot as the present peak, but around 0,15 K colder.

This is "obvious" to you, perhaps but with this info in hand I think its possible that the 2000 - peak is in fact the hottest period since 1850 as we often hear.

BUT :-) since the 1850 temperatures were in very cold period of the Little iceages, and trend since then has been a return from a very cold period, the "warmest since 1850" is obviously a misleading overdramatised twist of the real situation.

The real situation is, that we are pehaps slightly slightly warmer now than the 1940 - warm peak, while the explosion of human CO2 took place in the 1950-60´ies. This does not really fit as evidence for anything.

now: The equilibrium thought: Yes, its true, both UHI and the supposed CO2 effect should according to somes lead to higher night temperatures, over land. But still , if UAH measures more heat that land based temps, it certainly points more to UHI and other problems for land based temps.

And then come RSS with a more muddy result... hmm. Science is not supposed to be simple :-)

K.R. Frank
20-12-2010 00:16
interesting posts, very civil

I have a couple of questions on the global mean calculations, I am not well informed on the issue or the terminology.

How are the global means calculated across the different methods? (as in where do the temp. data points come from)
Have we geographically selected fixed points around the globe to calculate the temp.? if so are these arbitrary or has some rationale been applied)
Can a single global figure have any meaning for a dynamic system such as the climate?
I find it hard to imagine that it can but then again I am not that well informed.
RE: Global Weather29-05-2012 19:10
Thanks for this wealth of climate information and for your analysis. That makes a good theory.

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