Selected significant climate events and anomalies for September 2015. Graphic: NOAA / NCDC

By: Jeff Masters
21 October 2015 (wunderground.com) – September 2015 had the largest departure of temperature from average of any month among all 1629 months in the record that began in January 1880, said NOAA’s National Centers for Environmental Information (NCEI) on Wednesday. (Note that since July and August are typically the warmest months globally in absolute terms, September was not Earth’s warmest month in that regard.) NASA rated September 2015 slightly cooler, as the 2nd warmest September on record, falling below September 2014’s mark. September 2015’s warmth makes the year-to-date period (January – September) the warmest such period on record, according to both NOAA and NASA. September 2015 was the fifth consecutive month a monthly high temperature record has been set in NOAA’s database, and the seventh month of the nine months so far in 2015. A potent El Niño event in the Eastern Pacific that crossed the threshold into the “strong” category in early July continues to intensify, and strong El Niño events release a large amount of heat to the atmosphere, typically boosting global temperatures by at least 0.1°C. This extra bump in temperature, when combined with the long-term warming of the planet due to human-caused emissions of heat-trapping gases like carbon dioxide, makes it virtually assured that 2015 will be Earth’s second consecutive warmest year on record–with 2016 a good bet to exceed even 2015’s warmth. NOAA’s top ten warmest global monthly departures from average:

  1. 0.90°C, Sep 2015
  2. 0.89°C, Aug 2015
  3. 0.89°C, Mar 2015
  4. 0.89°C, Feb 2015
  5. 0.89°C, Jan 2007
  6. 0.87°C, Jun 2015
  7. 0.86°C, Feb 1998
  8. 0.85°C, May 2015
  9. 0.85°C, Mar 2010
  10. 0.84°C, Dec 2014

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September 2015: Earth’s Warmest Month in Recorded History, Says NOAA September 2015 blended land and sea surface temperature percentiles. Graphic: NOAA / NCDC

Global highlights: September 2015

  • The September average temperature across global land and ocean surfaces was 1.62°F (0.90°C) above the 20th century average. This was the highest September temperature on record, surpassing the previous record set last year by +0.12°F (+0.19°C). September’s high temperature was also the greatest rise above average for any month in the 136-year historical record, surpassing the previous record set in both February and March this year by 0.02°F (0.01°C).
  • The September globally-averaged land surface temperature was 2.09°F (1.16°C) above the 20th century average. This was also the highest for September in the 1880–2015 record, surpassing the previous record set in 2009 by +0.16°F (+0.09°C). Record warmth was observed across much of South America and parts of Africa, the Middle East, Europe, and Asia.
  • The September globally-averaged sea surface temperature was 1.46°F (0.81°C) above the 20th century average. This was the highest temperature for September in the 1880–2015 record, surpassing the previous record set in 2014 by +0.13°F (+0.07°C).
  • On September 11th, Arctic sea ice reached its annual minimum extent at 1.70 million square miles, the fourth smallest extent in the 1979–2015 satellite record, according to the National Snow and Ice Data Center. This was 699,000 square miles below the 1981–2010 average, but 394,000 square miles larger than the record small minimum that occurred in 2012.
  • The average Arctic sea ice extent for September 2015 was 720,000 square miles (28.88 percent) below the 1981–2010 average. This was the fourth smallest September extent since records began in 1979, according to analysis by the National Snow and Ice Data Center using data from NOAA and NASA. Below-average sea ice was observed across most regions of the Arctic, while near-average sea ice was observed in the Barents Sea.
  • Antarctic sea ice extent during September 2015 was 100,000 square miles (0.53 percent) below the 1981–2010 average. This was the 16th smallest Antarctic sea ice extent on record and smallest since 2008. The maximum Antarctic sea extent was not reached until the month of October, and will be reported next month.

Global highlights: Year-to-date (January–September 2015)

  • The year-to-date temperature across global land and ocean surfaces was 1.53°F (0.85°C) above the 20th century average. This was the highest for January–September in the 1880–2015 record, surpassing the previous record set in 2014 by 0.19°F (0.12°C).
  • The year-to-date globally-averaged land surface temperature was also the highest for January–September in the 1880–2015 record at 2.32°F (1.29°C) above the 20th century average. This value surpassed the previous record of 2007 by 0.31°F (0.17°C).
  • The year-to-date globally-averaged sea surface temperature was 1.24°F (0.69°C) above the 20th century average and the highest for January–September in the 1880–2015 record. This value surpassed the previous record of 2010 by +0.11°F (+0.06°C). For extended analysis of global temperature and precipitation patterns, please see our full September report

Global Summary Information – September 2015