|Above: September global temperature departures from 1951-1980 average over the globe, in degrees Celsius, according to NASA's Goddard Institute for Space Studies GISTEMP analysis. Image credit: NASA/GISS.
In its global State of the Climate report issued Wednesday, NOAA reported that last month was tied with September 2015 as the warmest September on record in data going back to 1880. Other agencies agreed that last month was near the top, although their placements varied slightly. Minor differences in rankings can arise because of how the various agencies handle data-sparse regions such as the Arctic, where few surface weather stations exist.
—NASA ranked last month as the second warmest September on record, just behind 2016 and ahead of 2015.
—The Japan Meteorological Agency found last month to be slightly cooler than 2015 and warmer than 2016, making it the second warmest September on record globally.
—The European Union’s Copernicus EU program placed last month as the warmest September on record in data extending back to 1979.
The bottom line is that last month was among the three warmest Septembers globally in 140 years of recordkeeping. As NOAA pointed out in a news release, “The 10 warmest Septembers have all occurred since 2005, with the last five years (2015-2019) being the five warmest Septembers on record.”
|Figure 1. Departures of global temperature for every September since 1880 compared to the 20th-century average. Image credit: NOAA/NCEI.
Last month’s global warmth is especially noteworthy given the absence of an El Niño event, which normally acts to boost global temperatures by transferring large amounts of heat from ocean to atmosphere. One of the strongest El Niño events ever observed pushed global temperatures to record levels in 2015-16.
For the year to date (January-September), NOAA ranks 2019 as the second warmest year on record, behind only the first nine months of 2016—which, again, were heavily influenced by the intense El Niño of 2015-16. The most likely outcome by year's end is that 2019 will be the second warmest full year on record, going back to 1880 (see embedded tweet below).
|Figure 2. Departure of global temperature from average for 2019 to date, compared to previous January-to-September periods going back to 1880. Record-warm Jan.-Sept. temperatures were observed across much of the southern half of Africa, the western Indian Ocean, Madagascar, and across parts of Australia, northern Europe, the western Pacific Ocean, New Zealand, Asia, the Atlantic Ocean, and North and South America. No land or ocean area had record cold year-to-date temperature departures from average. At this grid resolution, the only land area on Earth running cooler than average for the year to date is the north central United States. Image credit: NOAA/NCEI.
The current warmth is right in line with ongoing long-term warming related to human-produced greenhouse gases. According to NOAA, the year-to-date global temperature is 1.69°F (0.94°C) above the 20th-century average of 57.5°F (14.2°C). Global temperatures are now running more than 1°C above the levels observed in preindustrial times of the 19th century—a flashing warning sign, given the IPCC’s special 2018 report on the myriad risks to the stability of global climate and ecosystems if sustained warming exceeds 1.5°C above preindustrial values.
Global temperatures in 2019 will likely be between 1.1C and 1.2C warmer than the late 1800s in the @NASAGISS record. Warming to date has been around 1.1C globally, but 1.8C over land regions and 0.7C over ocean regions: 2/9 pic.twitter.com/2UzBeyF5h2— Zeke Hausfather (@hausfath) October 16, 2019
Standout events from September
—September had four billion-dollar weather disasters, bringing the tally for the year to 23. Ten of these 23 disasters have been in the U.S., making it the fifth year in a row for ten or more billion-dollar U.S. weather disasters—an unprecedented occurrence, even with inflation taken into account.
—One nation or territory (Guadeloupe) set an all-time heat record in September. As of October 15, all-time high temperature records have been tied or broken in nineteen of the world’s nations and territories, making 2019 the second most prolific year on record for all-time national heat records.
—Arctic sea ice extent during September was the third lowest in the 41-year satellite record; the annual minimum in sea ice extent occurred on September 18 and was tied with 2007 and 2016 for the second lowest yearly minimum on record, behind 2012. Because this autumn's refreeze has been so slow, Arctic sea ice extent was once again approaching record lows for the time of year as of October 15.
Full details on the record-breaking events for September 2019, and national/territorial heat records this year to date, are at Jeff Masters’ Eye of the Storm blog at Scientific American. We'll have an update on the Atlantic tropics in our next post.