GISS Adjustments In Iceland
By Paul Homewood
Following yesterday’s post about GHCN temperature adjustments in Iceland, GISS have now updated the latest numbers with the GHCN data, so we can look at the effect of the adjustments station by station.
For certain years GISS have no data, hence the gaps in the graphs. (This has been raised previously as an anomaly, as both GHCN and the Iceland Met do have figures for these years). But, basically, all three stations show a similar pattern , with the GHCN adjustments reducing temperatures in the years leading up to 1965. Intriguingly, as well, GISS now seem to ignore totally the high temperatures recorded in Reykjavik during the 1930’s and 40’s. They must be far too inconvenient!
One further thing I noticed though. GISS take the GHCN adjusted data and then adjust again themselves. The GISS adjustment is supposedly to take care of the UHI effect, as they explain
The GHCNv3/SCAR data are modified to obtain station data from which our tables, graphs, and maps are constructed: The urban and peri-urban (i.e., other than rural) stations are adjusted so that their long-term trend matches that of the mean of neighboring rural stations.
To do this, either past temperatures should be adjusted upwards, or current ones downwards. This would then offset the fact that, over the years, UHI has added a warming bias. But when we look at Reykjavik, we find that the opposite has occurred; past temperatures have been reduced instead of increased.
Since 1994, the before and after figures are the same. Up to 1971, though, the temperature was adjusted down by 0.5C, with a gradual reduction in the value of the adjustment thereafter. The relevant data can be accessed on the links below.
The effect of the GHCN and GISS adjustments is startling, as the three graphs below illustrate.
Before GHCN Adj
After GHCN Adj
After GISS Adj
GISS and GHCN, between them, have utterly corrupted the Icelandic temperature record beyond recognition.