An Introduction To The Hadley Centre’s New HADSST3 Sea Surface Temperature Data

The Royal Netherlands Meteorological Institute (KNMI) has added the Hadley Centre’s new Sea Surface Temperature (SST) dataset HADSST3 to their Climate Explorer. (Thanks to Dr. Geert Jan van Oldenborgh for the update.) The following post is a quick introduction to the revisions to their global SST data. We’ll take a look at the individual ocean basins in a future post.

The new dataset was introduced in a two-part Kennedy et al (2011) paper:

Reassessing biases and other uncertainties in sea-surface temperature observations measured in situ since 1850, part 1: measurement and sampling uncertainties

And:

Reassessing biases and other uncertainties in sea-surface temperature observations measured in situ since 1850, part 2: biases and homogenisation

Note: The HADSST3 data ends in December 2006. Hopefully the Hadley Centre will be able to update the data in the near future.

Figure 1 is a time-series graph that compares the new HADSST3 Global SST data to its predecessor HADSST2. The data have been smoothed with 13-month running-average filters to reduce the noise and the seasonal signal. The largest correction occurs in 1945 to account for the discontinuity presented in the Thomson et al (2008) paper Identifying Signatures of Natural Climate Variability in Time Series of Global-Mean Surface Temperature: Methodology and Insights.

Figure 1

By subtracting the Global HADSST2 data from the HADSST3 data, Figure 2, the magnitude of the correction at that time becomes apparent. The Hadley Centre appears also to have increased the response to the 1883 eruption of Krakatoa, and reduced the rise from 1920 to 1940.

Figure 2

The long-term linear trends of the Global HADSST3 data are basically the same as HADSST2 at about 0.335 deg C per Century, as shown in Figure 3.

Figure 3

Let’s take a look at the trends during the two 20^thCentury (plus) warming epochs and the mid-century cooling period. From January 1975 to December 2006, Figure 4, the global HADSST2 and HADSST3 linear trends are basically the same at 0.16 deg C per decade.

Figure 4

The corrections made to the early warming period, Figure 5, has reduced the linear trend for the period of January 1910 to December 1941 from 0.165 deg C per decade for the global HADSST2 data to 0.137 deg C per decade for the HADSST3 data.

Figure 5

The biggest change, of course, occurs during the mid 20^thCentury cooling period. Figure 6 illustrates the Global SST anomalies for the two HADSST datasets for the period of January 1941 to December 1975. By correcting the discontinuity in 1945 and gradually aligning the data again in the early 1970s, the linear trend has dropped drastically from -0.008 deg C per decade for HADSST2 to -0.033 deg C per decade for the global HADSST3 data.

Figure 6

And that’s the period the IPCC models have difficulty reproducing. Figure 7 is a comparison of the global HADSST3 data to the IPCC Multi-Model Mean (20C3M) for the mid-century cooling era.

Figure 7

SOURCE

The IPCC Multi-Model Mean TOS data and the data for the two Hadley Centre SST datasets are available through the KNMI Climate Explorer:

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