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.
Which still leavers us with the question – “Why is ther a higher than usual peak at intervals of 30 to 37 months?” Murray
I like the stream-of-consciousness approach to issues on blogs like WUWT, Lucia’s The Blackboard and CA. We can see the processes, problems and pitfalls in near real time, rather than being handed results with assurances that everything was done correctly. I suppose that that is the main issue I have with much of mainstream climate science: we are presented with black box results.
This actually is a nice delineation of the difference in mindsets between skeptics and advocates. A skeptic being someone willing to question and still willing to accept reasonable conclusions. When advocates find a mistake they cover it, obfuscate and claim it makes no difference until they cannot.
Thanks Dr. Spencer for your honesty in this. It’s been a very interesting series of posts to say the least.
thanks for the support, guys…and sorry for the whiplash on the SST subject.
BTW La Nina is just showing us one leg (in her way back):
http://www.cgd.ucar.edu/cas/catalog/climind/soi.html
Flanagan (02:44:21) : .. It’s always great to see that two different means of measurement actually lead to the same conclusions… And I hope it will make people understand that hasty analyses and conclusions should not form the basis of any scientific approach. I wonder where all the rumors of data manipulaiton will go now…
Yes it is great when another means of measurement confirms the other. Satellite air temperatures were confirmed with radiosondes I believe and AMSR_E with the bouys. I’m afraid you have picked up the wrong message here. You seem to think that surprising results should never be questioned, in fact all results should always be, and cross checked rigourously.
Doubts about data manipulation will always remain and they should after the infamous hockey stick episode. Besides this there is always the possibility of inadvertent errors. Scepticism is one of the instruments through which science advances.
Finally it does not change the broad picture. Looking at the Earth’s climate over several million years we can see a cooling trend, with the preponderance and inevitability of the ice-ages and the complete absence of any run-away global warming.
Reading disaster from the records of a few decades which remain part of a longer term trend remains dubious.
Bill in Vigo (05:30:03) “It would be a good thing if more of our researchers would add a good statician to their “teams” to perhaps increase the validity of their computations.”
Be careful with that. Academic-level Statistics is a dreamy field. The culture in the discipline leads to methods that lean heavily on untenable assumptions. Crazy assumptions are the problem – i.e. when something complex is not yet understood, that does not mean it is random or that it conveniently follows some abstract notion (despite widespread dreamy mainstream-science conventions that could easily get a practicing engineer in serious trouble).
It is important to keep in mind that each discipline has an interest in its own survival and that trends in methodology within disciplines (particularly the abstract ones) are largely driven internally. Funding structures have created this jealous & selfish mess which interferes with interdisciplinary research.
We may yet need to tear into the university education & research system with firm resolve to restructure it to address interdisciplinary challenges.
Nogw (12:00:18)
BTW La Nina is just showing us one leg (in her way back):
http://www.cgd.ucar.edu/cas/catalog/climind/soi.html
Are you interpreting negative values of SOI as indicative of La Nina?
Lucy Skywalker, I see Ninderthana’s interesting comment in response to your question. Perhaps the mechanism he suggests is working in concert with the other interesting theory being tossed around here lately – i.e. that currently-strong ocean-atmosphere gradients are related to solar minimum and that this has the oceans presently in a state of discharge without net replenishment.
Whatever is happening, I’ve absolutely no doubt whatsoever that natural climate is dramatically more complex than some would like the masses to believe.
–
Comment about the solar minimum / SST theory:
My request of the proponents is this:
Explain why the pattern is reversed pre-1930 (all the way back to 1770). This is not something that can be swept under a rug – on the contrary: it should be a key focus. The fact that it works like a switch that flips to anti-phase-relations is a big clue about something very important. I don’t have a theory ready for presentation, but this is on my mind. For those pondering this: I refer you to the works of Russian scientist Yu.V Barkin and wish you efficient, penetrating insight.
Best Regards.
Re: Bob Tisdale (01:03:57)
Bob you’re doing a great job with your blog. I was just looking at…
“Sea Level Data In Monthly Format”
http://bobtisdale.blogspot.com/2009/07/sea-level-data-in-monthly-format.html
…and wishing I had some time to run some basin- & region-wise contrasts – i.e. Pac-Atl, Pac-Ind, Atl-Ind, & others — for example I’m curious to compare the 70S, 70W area with others after reading several of the recent works of Yu.V. Barkin. (I’m saving the task for a clearer day in case I run into time-sucking data-format issues, as per your comments.)
Such contrasts will yield valuable clues about the spatiotemporal rhythm of the hydrologic cycle (which is a major factor interfering with efforts to understand solar-terrestrial relations).
I’ll keep an eye on your blog in case you beat me to the contrasts.
Down goes the DMI temp above 80N and across level goes the AMSR-E sea ice extent.
All,
Up top, someone was musing about using blogs vs “peer reviewed” and the result of that in light of this “whiplash” episode.
FWIW – Dr. Spencer’s comment “sorry about the whiplash” to me is why the blog process is an important stop in any scientific investigation. A couple of reasons off the top of my head:
1. The audience is wide with many different backgrounds, education levels and beliefs (yes they do count in how we think). In the blog environment the scientist can rub shoulders with someone who asks an innocent question from ignorance which sparks a new avenue of questioning the data.
2. It’s informal – the trappings of academia drop away and anyone can express an opinion, and, if stated with some civility, get an audience to respond.
3. It prevents the “I have a mind like a steel trap, rusted shut” syndrome because someone is always ready to pick apart the conclusion, and while that can get annoying, it often helps to cause questions.
4. It is an open rather than closed discussion. I see few are swayed by the Dr. in front of the names here. That allows us to converse as human beings rather than sycophants looking to the all powerful Oz for enlightenment.
Whiplash? I think not, simply and ebb and flow of a process.
The conversation here may have prevented a really good scientist from getting egg on his face, which would have hampered any future discussions of AGW.
I’ll shaddup now…
Mike
RobP (05:58:33) – Blogs can’t always replace good peer review. Review in some busy blogs with attentive participants can find some problems. But if an RC team member posts on a place like RC, he’ll mostly get echoes of agreement…and disagreements will be deleted (assuming anyone who disagrees still reads there). At most blogs there aren’t enough readers to matter.
However, similar technologies can be used to help communication between a group of participants. Whether the discussion is also open to the public is a policy decision.
Errors in statistical manipulation of any of this stuff seems equal to the “measured CO2 signal”. Dr. Spencer demonstrates this. I think before AGWer’s speak of a warming signal, someone needs to come up with a standard error of measurement for what some are saying is a warming signal.
Richard (12:12:57) :
Bravo. Well said.
Chris
Norfolk, VA, USA
A new 2,000-year-long reconstruction of sea surface temperatures (SST) from the Indo-Pacific warm pool (IPWP) suggests that temperatures in the region may have been as warm during the Medieval Warm Period as they are today.
http://www.sciencedaily.com/releases/2009/08/090827131832.htm
Hey I thought the Medieval warm Period (according to the warmers) was only a local phenomenon? But here it appears in the “the largest body of warm water in the world, and, as a result, it is the largest source of heat and moisture to the global atmosphere, and an important component of the planet’s climate.”
savethesharks (19:43:16) : Thank you Chris.
If Arctic sea ice is any indicator of ocean temperatures then July does seem to have been a warm period for sea surface temperatures.
I am keeping a record of sea ice extents and melting. In July the melt this year exceeded the July 2008 melt by 311,719 sq kms.
However from precisely this date (the 27th of July) this year, the trend reversed and the melt today is 459,063 sq kms less than the same day last year.
The total difference from the 27th of july – 870,000 sq kms. (870,000 sq kms less ice melted from that day, which seems pretty significant to me)
I’m not offering any explanation. Just an observation. Does anyone have any solar data that matches these dates?
Sorry that should be 770,000 sq kms not 870,000
Richard: are you sure you shouldn’t be substracting those numbers?
Flanagan (22:38:17) : No on the 27th of july the ice was 311,719 sq kms LESS than the ice at the same date last year. ever since that day the melt has been less than last year and on the 1st of Sept the ice was 459,063 sq kms MORE than that last year.
Sorry I said the MELT was less – the way I put it was confusing.
This seems to be borne out by the people actually traversing the passage. “”Despite predictions from a top U.S. polar institute that the Arctic Ocean’s overall ice cover is headed for another ‘extreme’ meltdown by mid-September, the Environment Canada agency monitoring our northern waters says an unusual combination of factors is making navigation more difficult in the Northwest Passage this year after two straight summers of virtually clear sailing.”
Re: RobP (05:58:33) & Michael J. Bentley (16:03:01)
Thank you for sharing these interesting comments.
http://www.thepoles.com/news.php?id=18586
Richard, ice extent and area can shift and look like melt when it is actually compaction or movement into another area due to wind.
It did seem that the error you found in the first data sets could have easily been a cooling bias rather than a warming one.
Thank you clearing it up, however maybe you should also edit the original post as many may go there and not read the follow up?