September 2016 hottest on record: NASA

Last month was the warmest September in 136 years of record-keeping, meaning 11 of the past 12 consecutive months dating back to October last year have set new monthly high-temperature records, NASA said.

According to a monthly analysis of global temperatures by scientists at NASA's Goddard Institute for Space Studies (GISS) in the US, September 2016's temperature was a razor-thin 0.004 degrees Celsius warmer than the previous warmest September in 2014.

The margin is so narrow those two months are in a statistical tie. Last month was 0.91 degrees Celsius warmer than the mean September temperature from 1951-1980.

The record-warm September means 11 of the past 12 consecutive months dating back to October 2015 have set new monthly high-temperature records.

Updates to the input data have meant that June 2016, previously reported to have been the warmest June on record, is, in GISS's updated analysis, the third warmest June behind 2015 and 1998 after receiving additional temperature readings from Antarctica.

The late reports lowered the June 2016 anomaly by 0.05 degrees Celsius to 0.75.

"Monthly rankings are sensitive to updates in the record, and our latest update to mid-winter readings from the South Pole has changed the ranking for June," said GISS director Gavin Schmidt.

"We continue to stress that while monthly rankings are newsworthy, they are not nearly as important as long-term trends," said Schmidt.

The monthly analysis by the GISS team is assembled from publicly available data acquired by about 6,300 meteorological stations around the world, ship- and buoy-based instruments measuring sea surface temperature, and Antarctic research stations.

The global temperature record begins around 1880 because previous observations did not cover enough of the planet.

Monthly analyses are updated when additional data become available, and the results are subject to change, NASA said.