“Mean” is the statistical term for “average. The “running mean” averages each successive periods like, January through December, February though January, March through February, etc. The 12-month running mean shows the peak of El Nino in early 2017 at about 1.34 C.
Feedbacks kick in: 2017 is second warmest without El Niño influence
by Bruce Melton
First published on The Rag Blog, February 1, 2018
NOAA, the UK Met, and World Meteorological Organization (WMO) have all stated that 2017 was third warmest. But these three organizations use data that only averages temperature in the Arctic out to 150 miles from reporting stations. This is a big problem when thousands of miles of Arctic Ocean have no weather reporting stations and we know from those reporting stations that the Arctic is warming at least twice the global rate.
In 2010, NASA began using a polar temperature averaging approach that looks out 750 miles from reporting stations to better capture polar warming.