October 2017 was Earth's fourth warmest October since record keeping began in 1880

Dr. Jeff Masters · November 17, 2017

October 2017 was Earth's fourth warmest October since record keeping began in 1880, said NOAA's National Centers for Environmental Information (NCEI) on Friday. NOAA rated the five warmest Octobers since 1880 as being 2015, 2014, 2016, 2017, and 2003 (tied with 2017.) NASA rated October 2017 as the planet’s second warmest October on record, with the only warmer October coming in 2015. 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 October, according to NOAA, and global land temperatures were the eleventh warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the warmest for any October in the 39-year record, according to the University of Alabama Huntsville (UAH) and Remote Sensing Systems (RSS).

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Third-warmest year on record thus far

Each of the first ten months of 2017 have ranked among the top four warmest such months on record, giving 2017 the third highest January–October temperature in the 138-year record: 1.33°C (2.39°F) above the 20th-century average. This is behind the record year of 2016 by 0.18°C (0.33°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 very 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 will be the second or third warmest year in recorded history. 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 October 2017 was the fifth lowest in the 38-year satellite record, according to the National Snow and Ice Data Center (NSIDC). Sea ice surrounding Antarctica reached its yearly maximum extent on October 12, and had the second lowest maximum extent on record, behind 1986.

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