Spurious SST Warming Revisited
Dr. Roy Spencer August 31st, 2009
My previous post described what I called “smoking gun” evidence of a spurious drift in the NOAA sea surface temperature (SST) product when compared to SSTs from the TRMM satellite Microwave Imager (TMI). The drift seemed to be mostly confined to 2001, almost a ’step’ jump. The moored buoy validation statistics of the TMI sea surface temperatures from Frank Wentz’s web site (SSMI.com) suggested that the TMI SSTs had good long-term stability.
But 2001 was also the year that the TRMM satellite was boosted into a higher orbit, which concerned me. I asked Frank about the effect of this event on the TMI SSTs (which also come from his web site). Frank couldn’t remember the details, but said he spent quite a bit of time correcting for the altitude change on the retrieved SSTs since the microwave emission of the sea surface depends upon the TMI instrument’s view angle with respect to the local vertical.
I know from our many years of work together on the AMSR-E Science Team that Frank is indeed a careful researcher, yet it seemed like more than a coincidence that the TMI and NOAA sea surface temperatures diverged during the same year as the orbit boost. So, I went back to see what might have caused the problem. I went back and thought about the different ways in which one can compute area averages from satellite data.
To make a long story short, because the orbit boost caused the TMI to be able to “see” to slightly higher latitudes, the way in which individual latitude bands are handled has a significant impact on the resulting temperature anomalies that are computed over time. The previous results I presented were for the 40N to 40S latitude band, which is nominally what the TMI instrument sees today. But before 2001, the latitudinal extent was slightly smaller than it was after 2001.
As shown in the following figure, if I restrict the latitude range to 38N to 38S, which was always covered during the entire TRMM mission, I find that the divergence between the TMI and NOAA average SST measurements essentially disappears.
Even though I was processing the NOAA and TMI datasets in the same manner, I should NOT have been. This is because there were not as many gridpoints over cooler SST regions going into the ‘global’ averages before the satellite altitude boost as after the boost. So, for example, one must be very careful in computing a latitude band average, say from 39N to 40N, to make sure that there has been no long-term change in the sampling of that band.
Based upon the above comparisons, I would now say there is no statistically significant difference in the SST trends since 1998 between TMI, the NOAA ERSSTv3b product, and the HadSST2 product. And it does look like July 2009 might well have experienced a warmer SST anomaly than July 1998, as was originally claimed by NOAA. (Remember, TMI can not see all of the global oceans, just equatorward of about 40 deg. N and S latitude.)
In the bottom panel of the above figure, I also have a comparison between the TMI and AMSR-E sea surface temperatures, which are available only since June of 2002 from the Aqua satellite. As can be seen, there is no evidence of a calibration (or sampling) drift in that comparison either.
So, what’s the moral of this story? Always question your results…even after finding the obvious errors. And maybe I should eliminate the term ’smoking gun evidence’ from any results I describe in the future.
Oh…and don’t believe everything you read on the internet.
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Richard (00:20:36) :
Interesting that you saw fit to link to a two week old article which no longer has any relevance since all the yachts referred to have left the NW Passage. At the date it was published the Passage wasn’t clear last year either (see below). The Fleur Australe, which wasn’t mentioned in the article, had already passed through the ice and was in Gjoa Havn and is now anchored in Nome!
WEDNESDAY, 13 AUGUST 2008
The Plan
If such it could be said to be – we should be in Gjoa Havn this afternoon. The ice and weather are not looking at all good in the short term so we will wait in GH and see what happens. Options are to go back and look around the western and northern sides of King William and see whether we can get through to the west, or to nose out into James Ross Strait and feel the ice, or just to sit and wait for an easterly storm to open up a lead for us. If none of these, then we will have to park Berri somewhere for a possibly 50(F) below winter. I don’t know what facilities there are in GH, but I think that we might be able to get her out of the water in Cambridge Bay so contingency plans are hatching for any or all of the above. Appendages please – it’s early yet but not looking too rosy. If it all goes pearshaped, we will aim to be back in Cambridge Bay or GH by the end of September at the very latest.
What whiplash Dr Roy ?
We can dance as fast as you can; so don’t worry about us being able to adjust to your adjustments. Don’t you wish they had left the blasted satellite alone where it was ? I bet it even has a different orbital period than what it used to have, so I’m sure you will find some new knobs you have to tweak as well, to try and compensate for what those vandals did when they moved your gizmo.
But I can tell you are having fun doing this; so that is a good thing; we are certainly having fun keeping up with your adventures.
There’s a certain satisfaction that comes with figuring out what really is going on; so thank you for your diligence, and for letting us in on the progress.
There really is a law of unintended consequences; when you change something; it’s a bit like Oliver Cromwell’s axe, in the British Museum. It has only had two new heads, and five new handles since Oliver last used it !
George
Of course the obligatory question is, what’s wrong with the data now? 🙂
Phil. (08:51:53) : Interesting that you saw fit to link to a two week old article which no longer has any relevance since all the yachts referred to have left the NW Passage.
Phil was any yacht referred to in that quote? It compares this years ice to the last.
I dont remember if the Fleur Australe had already passed the passage, but if they had then that confirms that conditions got worse after that, when they should have got better. And the Fleur Australe had a mighty tough time getting through. It wasnt a “clear passge” like the last two years.
Can you post a link to that bit you have posted?
Ok found it and here is the very next post on the same date:
“Wednesday, 13 August 2008 The Berri is going for it!
I just talked to Alex on the sat phone.
He just received my “It’s open” message. ..Alex was very excited about the ice report. The full length of western coast Boothia is open or very thin (East side of Ross- Larsen- Franklin). The Berri is going to skip Gjoa Haven and move up into Ross for the attempt…” and on the 18th of August they got through. They went north of Baffin Island which is blocked this year.
Phil please dont quibble over inconsequential stuff.
Focus on whether or not records were broken might be missing the more important issue.
In the eyes of an administrator, strength usually takes precedence over truth…
–
Exaggerated scenario for the purpose of illustration:
If temperatures suddenly doubled, I would suspect natural causes.
The problem is that the public has been conditioned to think like this:
“If temperature goes up, it means anthro-CO2 is the cause.”
Like screwy economic models based on bad assumptions, this overly-simplistic reasoning constitutes a threat to civilization.
The arrival of the information age does not mean common sense can be abandoned – rather, it means that we now have easy access to statistics that are orders of magnitude more difficult to interpret sensibly.
Richard (11:51:59) :
Phil. (08:51:53) :” Interesting that you saw fit to link to a two week old article which no longer has any relevance since all the yachts referred to have left the NW Passage.”
Phil was any yacht referred to in that quote? It compares this years ice to the last.
So you didn’t read the piece before you linked it? The title is ‘Northwest Passage wrap-up: Boats blocked by ice in Gulf of Amundsen’, the first two sentences name 4 boats and is headed by a photo of three of them!
I dont remember if the Fleur Australe had already passed the passage, but if they had then that confirms that conditions got worse after that, when they should have got better. And the Fleur Australe had a mighty tough time getting through. It wasnt a “clear passge” like the last two years.
It confirms nothing of the sort, they sailed along a lead (just like last year) which either closed or the later yachts picked a wrong line. Last year was not a “clear passage” either, here’s Berrimilla’s description of their passage last year a couple of days later:
“The Berri is just below the tip of the Tasmania Islands. Ice all around, “it’s a wall” but they can see one small opening to the NW. That is consistent with the ice charts and so that is where he will be heading.
Last night, Alex steered to”what seemed sensible” and is still underway.The Amodino is not so lucky.
The Berri crew has all been up all night dodging/fighting ice. They have not had time to do anything but handle the boat. (And I would hope to think- a quick bite) The call was short as Alex had to return to deck at once. He sounded tired and stressed. A long, long few miles and they will be out of it.
……….
The Amodino is stuck in the ice. They are much larger and can hopefully push their way around. Good luck to them. The Berri is too small and under powered to help, if there was a prayer to get close enough to help. ……….
Ice this dense,1/10 to 2/10, doesn’t just float around, it plays bumper penguin. One moving piece bumps into the next stopping but causes the next piece to take off, and so on. Openings close quickly and new opening happen just as fast.”
Richard (12:09:54) :
They went north of Baffin Island which is blocked this year.
No it isn’t, but this year the W-E yachts went through Bellot which was open this year but not last year and cuts some distance off the trip.
Phil please dont quibble over inconsequential stuff.
Well I suggest that you stop posting such inconsequential stuff then>
Phil. (22:06:58) – Whatever
Dr Spencer, You had posted a while back that you thought that there was a spurious warming of 0.2 C in the SST anomalies. Then you said you were mistaken.
However I just came across this little piece of information which made me wonder.
“..to enable them to make the case the oceans are warming, NOAA chose to remove satellite input into their global ocean estimation and not make any attempt to operationally use Argo data in the process. This resulted in a jump of 0.2C or more and ‘a new ocean warmth record’ in July.”
According to this NOAA has not used Argo data in computing their anomaly and with the Argo data the July temperature would have been 0.2C less.
Would you care to comment on this?
Regards
Richard