New GHCN Version Cools The Past Even More

By Paul Homewood

GHCN have just released their latest Version 3.2 and guess what? Yes, that’s right, they’ve cooled the past again, as the pink rash on the map shows.

Readers will recall that the previous version 3.1 was issued last November and produced a number of discrepancies that were never explained by GHCN, such as a large number of significant adjustments in the Arctic , nearly all of which cooled the past, thus creating a spurious warming trend.

They have now reworked some of their software, but instead of correcting these errors, they seem to have added to them.

So what is the overall effect of these changes? According to their technical log

How does this version of GHCN‐Monthly compare to the previous version? The September 2012 release of v3.2.0 has no effect on the unadjusted (raw) data and little effect on global temperature rankings based on the adjusted data. However, the century‐scale global land surface air temperature trend is higher using the adjusted v3.2.0 data. With v3.1.0, the adjusted annual global land surface air temperature trend for 1901‐2011 was 0.94°C/Century. Using data from version 3.2.0 this trend is 1.07°C/Century. The greatest differences between the two versions of the adjusted datasets are in the data for years prior to 1970. There is little difference in the global surface temperature trend during the 1979‐2011 period.

So the warming trend has just been increased by 0.13C/century. And remember this is on top of previous adjustments.

Let’s just recap why, in theory, these adjustments are made. GHCN explain thus

Surface weather stations are frequently subject to minor relocations throughout their history of operation. Observing stations may also undergo changes in instrumentation as measurement technology evolves. Furthermore, observing practices may vary through time, and the land use/land cover in the vicinity of an observing site can be altered by either natural or man-made causes. Any such modifications to the circumstances behind temperature measurements have the potential to alter a thermometer’s microclimate exposure characteristics or otherwise change the bias of measurements relative to those taken under previous circumstances. The manifestation of such changes is often an abrupt shift in the mean level of temperature readings that is unrelated to true climate variations and trends. Ultimately, these artifacts (also known as inhomogeneities) confound attempts to quantify climate variability and change because the magnitude of the artifact can be as large as or larger than the true background climate signal. The process of removing the impact of non-climatic changes in climate series is called homogenization, an essential but sometimes overlooked component of climate analysis.

So let’s look at two of the discrepancies we identified in Version 3.1, where an artificial warming trend had been introduced, Alice Springs in Australia and Vestmannaeyja in Iceland. The new Version 3.2 still seems to produce the same discrepancies.

The graphs on the right hand side tell the story. The top graph gives the raw temperatures, while the middle one shows adjusted temperatures. The bottom one plots the value of the adjustment, with blue indicating temperatures have been adjusted down, and red up. Although the scale is not very clear, in both cases temperatures up to about 1940 have been cooled, and more recent ones increased.

This has resulted in an artificial warming trend of nearly 2C in Vestmanneyja, while the adjustment is even greater in Alice Springs.

Previous work on this topic has already proven that there is no justification for these adjustments and that the original record is reliable – see here and here.

If the new version has failed to correct such obvious errors from Version 3.1, can there be any confidence that Version 3.2 does not contain even more?