Posted by drj | Filed under announcement
Tamino gives his results for his GHCN based temperature reconstruction. It is well worth reading. He also gives a comparison between stations that are reporting after 1992, and those that “dropped out” before 1992. He concludes that there is no significant difference in the overall trend. In other words refuting the claim that the 1990s station dropout has a warming effect. His results are preliminary and for the Northern Hemisphere only.
Tamino’s analysis use only the land stations; in order to write this blog post I tweaked ccc-gistemp so that we can produce a land index (python tool/run.py -s 1-3,5 now skips step 4, avoids merging in the ocean data, and effectively produces a global average based only on land data).
It is very easy to subset the input to ccc-gistemp and run it with smaller input datasets. So in this case I can split the input data into stations reporting since 1992, and those that have no records since 1992, and run ccc-gistemp separately on each input. I created tool/v2split.py to split the input data. Specifically I ran step 0 (which merges USHCN, Antarctic, and Hohenpeissenberg data into the GHCN data) to create work/v2.mean_comb then split that file into those stations reporting in 1992 and after, and those not reporting after the cutoff. Then I ran steps 1,2,3, and 5 of ccc-gistemp to create a land index:
It is certainly not the case that the warming trend is stronger in the data from the post-cutoff stations. [edit 2010-03-22: In a subsequent post I add trend lines to this chart]
The differences between these results and Tamino’s are interesting. Both show good agreement for most of the 20th century. These data show more divergence than Tamino’s in the 1800′s. Is that because we’re using Southern Hemisphere data as well, or is it because of the difference in station combining? Further investigation is merited.
We hope to make “experiments” of this sort easier to perform using ccc-gistemp and encourage anyone interested to download the code and play with it.
Update: Nick B obliges with a graph of the differences: