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Thursday, September 17, 2009

Record Sea Surface Temperatures Are Only In NOAA ERSST.v3b Dataset

I’ve moved to WordPress.  This post can now be found at Record Sea Surface Temperatures Are Only In NOAA ERSST.v3b Dataset
The NOAA press release claims the August Global Sea Surface Temperature (SST) was the warmest on record.

The record ERSST.v3b SST for August can be seen in Figure 1.
Figure 1

And of course SST anomalies, Figure 2, were also at record levels in August 2009.
Figure 2


August 2009 SST, Figure 3, and SST anomalies, Figure 4, for the NOAA satellite-based OI.v2 SST dataset were not records. NOAA writes about the Optimum Interpolation (OI.v2) data, “The optimum interpolation (OI) sea surface temperature (SST) analysis is produced weekly on a one-degree grid. The analysis uses in situ and satellite SST's plus SST's simulated by sea-ice cover. Before the analysis is computed, THE SATELLITE DATA IS ADJUSTED FOR BIASES using the method of Reynolds (1988) and Reynolds and Marsico (1993).” [Emphasis added.]
Figure 3
Figure 4

NOAA does not use satellite data in its ERSST.v3b SST dataset. However, when NOAA originally released the ERSST.v3b dataset in 2008, they included satellite data to supplement the buoy- and ship-based data. This was discussed in my post “Recent Differences Between GISS and NCDC SST Anomaly Data And A Look At The Multiple NCDC SST Datasets” and repeated here:

In “Improvements to NOAA’s Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006)”, Smith et al note the use of satellite data for ERSST.v3 data in their abstract, “Beginning in 1985, improvements are due to the inclusion of bias-adjusted satellite data.” That’s a positive description. They further proclaim, “Of the improvements, the two that have the greatest influence on global averages are better tuning of the reconstruction method and inclusion of bias adjusted satellite data since 1985.” In fact there is a whole subsection in the paper about the satellite adjustments.

But the satellite data was removed because it was felt the satellite data caused a downward bias. Reynolds, Smith, and Liu write in a November 14, 2008 attachment to their main ERSST.v3b webpage, “In the ERSST version 3 on this web page WE HAVE REMOVED SATELLITE DATA from ERSST and the merged product. The addition of satellite data caused problems for many of our users. Although, the satellite data were corrected with respect to the in situ data as described in reprint, there was a residual cold bias that remained as shown in Figure 4 there. The bias was strongest in the middle and high latitude Southern Hemisphere where in situ data are sparse. THE RESIDAL BIAS LED TO A MODEST DECREASE IN THE GLOBAL WARMING TREND AND MODIFIED GLOBAL ANNUAL TEMPERATURE RANKINGS.” [Emphasis added.]
The link for that quote is here:http://www.ncdc.noaa.gov/oa/climate/research/sst/papers/merged-product-v3.pdf

Note that the “merged product” referenced above is their ERSST.v3b-based land plus sea surface temperature data.


The Hadley Centre’s HADSST2 does not show record SST anomalies for July, August, or for the Summer of 2009. Far from it. Refer to Figure 5. The Hadley Centre uses different techniques to smooth and infill missing data. The differences between the Hadley Centre and NOAA methodologies are explained in the NOAA paper about the ERSST.v3b data, “Improvements to NOAA’s Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006)”.
Figure 5


It appears that the methods used by NOAA to calculate Global SST in their ERSST.v3b dataset and the removal of the satellite data from those calculations created an upward bias.


NOAA’s ERSST.v3b SST anomaly data is available here:

NOAA’s ERSST.v3b SST data was downloaded from the KNMI Climate Explorer:

NOAA’s OI.v2 SST and SST anomaly data is available through their NOMADS website:

THE HADSST2 SST anomaly data is listed in the second column in the following webpage. The other columns list the uncertainty ranges for measurement and grid box sampling, for coverage, for bias, and for the combination of those uncertainties:


While doing a visual check of the sources against the graphs, I noticed a difference between the SST anomaly data presented by NOAA for the same dataset. I’m noting it in case someone else spot checks the graphs. The Monthly Global Ocean Temperature Anomalies (degrees C) uses 1901 to 2000 as base years, but the ERSST.v3b data uses 1971 to 2000. Confirmation here:

For those who want to split hairs, the difference in the base years changes the rankings of SST anomalies, Figure 6. But it has no impact on the SST data rankings.
Figure 6


Seth Y. said...
This comment has been removed by a blog administrator.
John said...

Bob -

Given the differences in the three data sets, which do you think is the most accurate?

I notice that oiv2 and hadsst2 have a .2 difference in anomaly levels - that seems pretty substantial to me (.3ish vs. .5ish). And ERSST has it at .35ish.

I am assuming, given that you use it for most of your data mapping, that you believe oiv2 is the most accurate?

At some point do you think you'll switch to Aqua?

John said...

A followup - I may have figured out the hadsst difference - different base year, right? I just assumed they all had the same base year range, but it looks otherwise from the graphs.

The rest of my questions stand. :)

Bob Tisdale said...

John: I would have no idea which dataset is more accurate. I originally used the ERSST.v2 data because I could download it for ocean grids that I defined from the NOAA NOMADS website. Then NOAA obsoleted the ERSST.v2 data and removed it from NOMADS. I then switched to OI.v2 data for my monthly updates. I also use it for short-term evaluations. And another advantage to the OI.v2 data is that it's available on a weekly basis, too.

I began using the KNMI Climate Explorer six or seven months ago and all major SST datasets are available through it.

Bob Tisdale said...

Seth Y: Sorry. No political comments on my blog. That's really the only policy I have. It's noted at the bottom of each page. It reads:

Comments that are political in nature or that have nothing to do with the post will be deleted.

D Kelly O'Day said...


I enjoy/ appreciate your detailed data analysis.

I'm curious, what software do you use for your plots?

Bob Tisdale said...

D Kelly O'Day: It's MS EXCEL.

John said...

Hi Bob -

I know you don't like to make predictions, but after reading pretty much every article on your site and finding them all fascinating, I just wanted to ask a sort of global (pun not intended) question. As always, I am not seeking to pigeonhole you or make you commit to something.

Assuming that a) the AMO continues it's downward swing and b) the major step up ENSO events will not recur and we will return to a more normal ENSO cycle, do you believe that SST temperatures should remain steady or even potentially descrease in the comining one to three decades?

On the other hand, if we see more large scale El Ninos, temperatures should (naturally) tend to increase via the step ups.

It seems that absent these two drivers, there is only a very minor increasing temperature trend (be it via CO2 or recovery from the little ice age or whatever you can attribute it to).

Just trying to distill a complicated topic.

Thanks in advance, and thanks for your hard work.

I really look forward to more of your analytical articles - hopefully more news articles won't interrupt your research too much. :)

Anonymous said...

Does anyone know if the surface observations from the ARGO floats are incorporated into any of these datasets? The paper describing the OI analysis says they include drifting buoys, but that was before most of the ARGO system was established.

Bob Tisdale said...

Anonymous: I have looked for and have not found anything that says they are included or excluded.

The paper for the ERSST.v3b data says the XBT data is included, but nothing about ARGO.


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Comment Policy, SST Posts, and Notes

Comments that are political in nature or that have nothing to do with the post will be deleted.
The Smith and Reynolds SST Posts DOES NOT LIST ALL SST POSTS. I stopped using ERSST.v2 data for SST when NOAA deleted it from NOMADS early in 2009.

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