Earth’s Second Warmest October on Record

November 18, 2019, 6:44 PM EST

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Above: Temperature departures from average for October 2019 as calculated by NASA’s Goddard Institute for Space Studies and mapped by Zachary Labe (University of California, Irvine). Image credit: Zack Labe, @ZLabe.

NASA, NOAA, and the Japan Meteorological Agency are in solid consensus that last month was the second warmest October in global records that extend back to the late 1800s. The agencies agreed that October 2019 came in just behind October 2015. The Copernicus EU office found that October was narrowly the warmest on record in its dataset, which extends back to 1979. Variations in how different groups analyze data-sparse regions such as the Arctic can lead to minor differences between groups in the rankings of a particular month.

The NOAA report, released on Monday, found that October 2019 was 0.98°C (1.76°F) above the 20th-century average and only 0.06°C (0.11°F) cooler than October 2015. The last five Octobers are the five warmest on record globally, according to NOAA, as evident in Figure 1. To find an October that was cooler than the 20th-century global average, you have to go all the way back to 1976.

Global temperature anomalies for October, 1895-2019
Figure 1. Departures from the 20th-century average temperature for each October since 1895. Image credit: NOAA/NCEI.

Also finding that last month was the second warmest October was the University of Alabama Huntsville, based on data from NOAA’s satellite-based Microwave Sounding Units for the lowest five miles of the atmosphere (the lower and middle troposphere). October 2017 is the warmest October in the UAH database, which goes back to December 1978.

NOAA found that areas of record-warm October temperatures were focused across parts of the northern and western Pacific Ocean and northeastern Canada, as well as scattered across parts of the South Atlantic Ocean, Africa, Europe, the Middle East, the Indian Ocean, and South America. Record cold for October was limited to a patch of the northwest U.S. (see "Standouts from October" below).

Departures from average temperature by region, Oct 2019
Figure 2. Departure of global temperature from average for 2019 to date, compared to previous January-to-September periods going back to 1880. Image credit: NOAA/NCEI.

With two months left to go, 2019 will likely come in as the second warmest year on record globally, according to NOAA, and it’s a virtual lock to be one of the five warmest years on record globally. If this happens, then the five warmest years in more than a century of recordkeeping, and perhaps for centuries before that, will be (not in this order) 2015, 2016, 2017, 2018, and 2019. This warmth is even more amazing considering that the sun has been in the declining phase of its least active 11-year activity cycle in more than a century. In their initial consensus forecast, a NOAA-NASA team is predicting that the next solar cycle is likely to be just as weak.

Standouts from October

One of the most extreme temperature contortions on the planet in October was the flip-flop between North America and the adjacent Arctic. Record warmth prevailed over the Arctic and adjoining Alaska and northern Canada, reinforced by still-unfrozen waters (especially over the Chukchi Sea, which has smashed records for delayed freeze-up). The National Snow and Ice Data Center reported that Arctic sea ice extent was the lowest on record for October as a whole, and ice volume also remains at ominously low levels.

Meanwhile, the upper-level ridging that helped keep the Arctic warm also funneled unusually chilly air into southern Canada and the central and western U.S. during much of October. Part of Scandinavia were also unusually cool. As we reported earlier this month, every contiguous state from Kansas northward and westward had one of its ten coolest Octobers on record, and it was Idaho’s coldest.

In the global perspective, the chill over parts of western North America stands out like a numb thumb. As Zack Labe (University of California, Irvine) put it, “Your backyard is not representative of global weather/climate.”

Another noteworthy event in October was the continuation of one of the strongest positive Indian Ocean Dipole (IOD) modes on record. Much like the El Niño/Southern Oscillation, the IOD features a semi-cyclic “sloshing” of warm water across the Indian Ocean. When the IOD is positive, unusually warm water extends west into the Arabian Sea, while the waters near Southeast Asia and Australia are cooler than average. October 2019's near-record IOD index makes 2019 one of three years in records going back to 1982 to see a monthly IOD value above 2.0°C.

Atop long-term oceanic warming, the strongly positive IOD led to unusually supportive conditions for tropical cyclones over the Arabian Sea. Cyclone Kyarr peaked on October 27 with sustained winds of 150 mph, according to the Joint Typhoon Warning Center, making it the second strongest cyclone on record in the Arabian Sea. As of November 18, the North Indian Ocean (including the Arabian Sea) had racked up a record 85.5 units of accumulated cyclone energy in 2019, almost six times more than the average to date of 14.9 units.

Also noteworthy: October had two billion-dollar weather disasters (Typhoon Hagibis in Japan and severe drought in China), bringing the tally for the year to 25. Ten of these 25 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.

Full details on the record-breaking events for October 2019, and national/territorial heat records this year to date, are at Jeff Masters’ Eye of the Storm blog at Scientific American.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Bob Henson

Bob Henson is a meteorologist and writer at, where he co-produces the Category 6 news site at Weather Underground. He spent many years at the National Center for Atmospheric Research and is the author of “The Thinking Person’s Guide to Climate Change” and “Weather on the Air: A History of Broadcast Meteorology.”

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