Thursday, April 26, 2007

Uncertainties in sea temperatures, “A gathering storm.”


Last year, a paper by Lyman, et al. was released, entitled “Recent cooling of the upper ocean”. At the time, one of the authors of the report considered it to be a global warming anomaly due to natural variability, Recent disclosures in technical issues in measurement suggest this is now level ie no change in prior reconstructions. That is a slight increase of 0.2-0.5c over the last 160 years.

Of course this suggests that there are no errors in sampling of datasets that prior reconstructions are based on. As the previous post shows there seem to be some inconvenient problems with sampling outside a narrow geographical region.5-15n
As seen on the image here



As we also noted there is degree of arbitrariness in the measurement process for SST reconstructions. Another is this.

Journal of Atmospheric and Oceanic Technology
Article: pp. 476–486 Toward Estimating Climatic Trends in SST. Part II: Random Errors

Elizabeth C. Kent and Peter G. Challenor

ABSTRACT

Random observational errors for sea surface temperature (SST) are estimated using merchant ship reports from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) for the period of 1970–97. A statistical technique, semivariogram analysis, is used to isolate the variance resulting from the observational error from that resulting from the spatial variability in a dataset of the differences of paired SST reports. The method is largely successful, although there is some evidence that in high-variability regions the separation of random and spatial error is not complete, which may have led to an overestimate of the random observational error in these regions. The error estimates are robust to changes in the details of the regression method used to estimate the spatial variability.

The resulting error estimates are shown to vary with region, time, the quality control applied, the method of measurement, the recruiting country, and the source of the data. SST data measured using buckets typically contain smaller random errors than those measured using an engine-intake thermometer. Errors are larger in the 1970s, probably because of problems with data transmission in the early days of the Global Telecommunications System. The best estimate of the global average random error in ICOADS ship SST for the period of 1970–97 is 1.2°C if the estimates are weighted by ocean area and 1.3°C if the estimates are weighted by the number of observations.

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