September 2017: Earth's 4th Warmest September on Record

Dr. Jeff Masters · October 18, 2017, 12:04 PM EDT

September 2017 was the planet's fourth warmest September since record keeping began in 1880, said NOAA's National Centers for Environmental Information (NCEI) and NASA this week. The only warmer Septembers came during 2015, 2016, and 2014. Minor differences can occur between the NASA and NOAA rankings because of their different techniques for analyzing data-sparse regions such as the Arctic.

Global ocean temperatures last month were the fourth warmest on record for any September, according to NOAA, and global land temperatures were the third warmest on record.

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Second-warmest year on record thus far

Each of the first eight months of 2017 have ranked among the top four warmest such months on record, giving 2017 the second highest January–September temperature in the 138-year record: 0.78°C (1.57°F) above the 20th-century average. This is behind the record year of 2016 by 0.13°C (0.24°F). This near-record warmth in 2017 is especially remarkable given the lack of an El Niño event this year. Global temperatures tend to be warmer during El Niño years, when the ocean releases more heat to the atmosphere. Given the lack of an El Niño event in 2017, it is unlikely that we will surpass 2016 as the warmest year on record. However, 2017 is almost certain to be the planet's warmest year on record that lacks any influence from El Niño, and Earth's four warmest years of the last century-plus are likely to be 2016, 2017, 2015, and 2014.

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Arctic sea ice extent during September 2017 was the seventh lowest in the 38-year satellite record, according to the National Snow and Ice Data Center

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Sea ice surrounding Antarctica had the second lowest extent on record in September 2017, and has been at record- to near-record lows since September 2016.

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