January-September 2016 was the hottest such period on record, at 0.89°C (1.60°F) above the 20th century average of 14.1°C (57.5°F), according to a new report from the U.S. National Oceanic and Atmospheric Administration.
Much-warmer-than-average conditions engulfed the vast majority of the world's land surfaces. Record warmth for this period was notable across Alaska and western Canada, southern Mexico into Central America, much of northern South America, large parts of eastern, south central, and southwestern Africa, central Asia and parts of northern Russia, and the islands of southeastern Asia.
The average global sea surface temperature for the year-to-date was the highest for January–September in the 137-year period of record, at 0.78°C (1.40°F) above average, surpassing the previous record set in 2015 by 0.08°C.
WMO uses a combination of datasets from NOAA, NASA’s Goddard Institute for Space Studies, the UK’s Met Office HadCRUT, as well as reanalysis data from the European Centre for Medium Range Weather Forecasting to compile its assessments on the climate.
The provisional assessment for 2016 will be released during the U.N. Climate Change negotiations in Marrakech in November.
NOAA said that the month of September was the second hottest on record, slightly behind September 2015.
The combined average temperature over global land and ocean surfaces for September 2016 was the second highest for September in the 137-year record, 0.04°C (0.07°F) cooler than the record warmth of 2015.
"A few months after the end of one of the strongest El Niños in at least the past half century, this month effectively snapped the 16-month streak of record warm monthly global temperatures," said NOAA.
It is not unusual that analysis disagree on the assessment because the underlying observations and methodologies are not exactly the same. This is why WMO combines various analysis in its annual assessment .