NOAA's August global SST record is the result of one data set

Yesterday NOAA announced with much fanfare that:

The world’s ocean surface temperature was the warmest for any August on record, and the warmest on record averaged for any June-August (Northern Hemisphere summer/Southern Hemisphere winter) season according to NOAA’s National Climatic Data Center in Asheville, N.C. The preliminary analysis is based on records dating back to 1880.

Besides the UAH data for August I cited, Bob Tisdale shows that some other datasets don’t agree with NOAA’s conclusion. – Anthony

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

Guest post by Bob Tisdale

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.

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Figure 1

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

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Figure 2

RECORD NOT CONFIRMED BY NOAA SATELLITE SST DATA

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.]

http://www.cdc.noaa.gov/data/gridded/data.noaa.oisst.v2.html

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Figure 3

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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 RESIDUAL 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.

RECORD NOT CONFIRMED BY ANOTHER SHIP- AND BUOY-BASED SST ANOMALY DATASET

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)”.

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Figure 5

CLOSING

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.

SOURCES

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

ftp://eclipse.ncdc.noaa.gov/pub/ersstv3b/pdo/aravg.mon.ocean.90S.90N.asc

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

http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere

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

http://nomad3.ncep.noaa.gov/cgi-bin/pdisp_sst.sh?lite=

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:

http://hadobs.metoffice.com/hadsst2/diagnostics/global/nh+sh/monthly

UPDATE

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:

http://www.ncdc.noaa.gov/oa/climate/research/sst/ersstv3.php

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.

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Figure 6