In case you missed it, I want to call your attention to an important essay by Werner Brozek posted last week on Anthony Watts’s blog, Watts Up with That (WAWT).
NASA supports two main satellite-based global temperature monitoring systems: the University of Alabama in Huntsville (UAH) program headed by John Christy and Roy Spencer, and the Remote Sensing Systems (RSS) program headed by Frank Wentz.
Climate activists have generally been boosterish about RSS and negative about UAH. The RSS found a mid-troposphere warming trend from the start of its satellite record in July 1987 whereas the UAH found a cooling trend from 1979 through 1995.
In 1998, Wentz published a study in Nature arguing that uncorrected instrument error associated with satellite orbital decay injected a spurious cooling bias into the UAH dataset. Spencer and Christy accepted the criticism, made the adjustment, and since 1998 their dataset has shown a long-term warming trend. However, at least through 2004, the UAH record showed less warming (0.09°C/decade) than the RSS record (0.12°C). So activists continued to take potshots at Spencer and Christy, implying (or asserting) that their political biases accounted for the discrepancy.
Ah, but how quickly the wheel turns! During the 2000s, the divergence began to go the other way as the RSS record showed less warming than the UAH record.
Which brings us back to Brozek and his post in WUWT. Brozek shows there has been no warming in the RSS data from Dec. 1996 through July 2013 — a 200 month warming pause.
Figure explanation: “The graphic above shows 3 lines. The long line shows that RSS has been flat from December 1996 to July 2013, which is a period of 16 years and 8 months or 200 months. The other slightly higher flat line in the middle is the latest complete decade of 120 months from January 2001 to December 2010. The other slightly downward sloping line is the latest 120 months prior from present. It very clearly shows it has been cooling lately, however this cooling is not statistically significant.“
Brozek examines all the major global temperature datasets and finds various periods during which “a slope that is at least very slightly negative ranges from 8 years and 7 months to 16 years and 8 months”:
- For GISS [NASA Goddard Institute for Space Studies], the slope is flat since February 2001 or 12 years, 6 months (goes to July).
- For Hadcrut3 [UK Hadley Meteorological Office Climate Research Unit], the slope is flat since April 1997 or 16 years, 4 months (goes to July).
- For a combination of GISS, Hadcrut3, UAH and RSS, the slope is flat since December 2000 or 12 years, 8 months (goes to July).
- For Hadcrut4 [a newer version of the Hadley surface temperature dataset], the slope is flat since December 2000 or 12 years, 8 months (goes to July).
- For Hadsst2 [Hadley sea surface temperature dataset], the slope is flat since March 1997 or 16 years, 4 months (goes to June).
- For UAH, the slope is flat since January 2005 or 8 years, 7 months (goes to July using version 5.5).
- For RSS, the slope is flat since December 1996 or 16 years and 8 months (goes to July).