>But They Fail To Tell You Why
The Met Office begins their December 10, 2009 press release…
…with, “A combination of man-made global warming and a moderate warming of the tropical Pacific Ocean, a phenomenon known as El Niño, means it is very likely that 2010 will be a warmer year globally than 2009.” They continue, “The latest forecast from our climate scientists, shows the global temperature is forecast to be almost 0.6 °C above the 1961–90 long-term average. This means that it is more likely than not that 2010 will be the warmest year in the instrumental record, beating the previous record year which was 1998.”
Most people would assume the “man-made global warming” portion of the opening sentence refers to anthropogenic greenhouse gases. But in this instance I believe “man-made” means the bias in the instrument temperature record, the Hadley Centre’s HADCRUT3GL data, the Hadley Centre created when they spliced two SST datasets together in 1998.
A year ago today, in the post The Step Change in HADSST Data After the 1997/98 El Nino, I plotted the differences between HADSST2 SST anomaly data and the SST anomalies of the three NOAA/NCDC SST datasets: ERSST.v2, ERSST.v3b, and OI.v2 datasets. Refer to Figures 1 through 3 for updated graphs.
The HADSST2 data acquired this man-made shift in Global SST data when they changed source SST datasets from ICOADS to NCEP-GTS in 1998. A coincidence? The supplier writes:
“The total period of record is currently 1784-May 2007 (Release 2.4), such that the observations and products are drawn from two separate archives (Project Status). ICOADS is supplemented by NCEP Real-time data (1991-date; limited products, NOT FULLY CONSISTENT WITH ICOADS).” [Emphasis added.]
Recently I also compared the global SST anomalies of HADSST2 and the other Hadley Centre’s SST dataset, HADISST, again plotting the difference between the two. Refer to Figure 4.
If the Global HADCRUT data is in record territory in 2010, it is in large part the product of poor source dataset splicing of the HADSST2 portion of the HADCRUT data. The period bias in their SST data varies from 0.06 to 0.12 deg C, depending on the dataset one uses for comparison.
The other portion of the record is the product of the multiyear aftereffects of the 1997/98 El Nino that I’ve discussed in numerous posts. The most recent overview of this is included in Global Temperatures This Decade Will Be The Warmest On Record….
ERSST.v2, ERSST.v3b, OI.v2, HADISST, and HADSST2 data is available through the LNMI Climate Explorer: