Data shows September was the warmest in modern temperature monitoring following months of record-breaking anomalies this year

Nasa has all but declared this year to be the hottest yet recorded, after September narrowly turned out the warmest in modern temperature monitoring.

Last month was 0.91C above the average temperature for that time of year from 1951 to 1980, the benchmark used for measuring rises.

The new findings follow record-breaking monthly anomalies throughout this year, leading the agency to believe that because of the highs reported so far, 2016 will take the crown as warmest in the 136 years of modern data-keeping.

Dr Gavin Schmidt, director of Nasa’s Goddard Institute for Space Studies, tweeted:

Gavin Schmidt (@ClimateOfGavin) With data now available through September, 2016 annual record (~1.25ºC above late 19th C) seems locked in. pic.twitter.com/Btp3Vutakn

Last month was only just over the previous record, coming in at a razor-thin 0.004C above the previous high for the time of year, reached in September 2014. That tiny margin may be revised in future, as monthly temperature data can be nudged up or down retrospectively as later reports come in. For instance, June 2016 was initially reported as the warmest on record but was subsequently revised downward slightly to the third warmest.

But it makes the trend for the year, and the long-term decadal trends, easier to discern. September’s high temperatures compared with the long-term average means that 11 of the last 12 consecutive months, back to October 2015, have set new records.

Last year was the hottest year since modern records began, brought about in part by a strong El Niño event, a Pacific weather system that can affect sea and air temperatures around the world, but also by strong underlying trends. Schmidt said earlier this year, when 2015’s status was confirmed, that it would have been the warmest year even without the El Niño.

July 2016 was the hottest single month since instruments have been reliably used to measure temperature, followed by a similar effect in August.

This year’s heat has continued to be affected by the tail-end of the El Niño weather phenomenon, as although the system has now dissipated, air temperatures tend to lag behind by several months.

If a new temperature record is set for 2016, it will confirm the longer term trends of climate change. This in turn will help scientists to counter claims from global warming sceptics that the rise in global temperatures has “paused” and therefore that climate change is not a threat.

The monthly reports from Nasa come from publicly available data from about 6,300 meteorological stations around the world, as well as measurements taken from ships and buoys at sea, and Antarctic research stations.

Other agencies, including the UK’s Met Office, the US National Oceanic and Atmospheric Administration and Japan’s Meteorological Agency, also publish temperature estimates. The Met Office forecast last December that this year would be the hottest ever, based on its observations. Also closely watched is the World Meteorological Organisation, which in July made a prediction that this year would be the hottest, based on data available to that date.

Final confirmation of whether this year is record-breaking is likely to come early next year.