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Another month, another monthly temperature record.
Global average temperatures for this past October blew past any previous marks, keeping the Earth on pace for its hottest recorded year, US researchers reported this week. The average was 0.98 degrees Celsius (1.76 Fahrenheit) over the 20th century average of 14 C (57 F) for the month, according to the National Oceanic and Atmospheric Administration (NOAA). Temperatures on both land and sea set monthly records, the agency said.
"This marked the sixth consecutive month a monthly global temperature record has been broken and was also the greatest departure from average for any month in the 1,630 months of record keeping," NOAA reported. The first 10 months of 2015 were also the warmest such period on record, the agency said — making it all but certain that the full year will top 2014 as the warmest in the books.
"There's really no chance, short of an asteroid hitting the planet or something like that, that we're not going to hit a record," said Andrew Dessler, an atmospheric science professor at Texas A&M University.
— NOAA NCEI Climate (@NOAANCEIclimate) November 18, 2015
400.31 parts per million (ppm) CO2 in air 17-Nov-2015 https://t.co/5Q2FLbb4ix
— Keeling_Curve (@Keeling_curve) November 18, 2015
A large part of this year's highs are due to the eastern Pacific warming phenomenon known as El Niño, which NOAA expects to peak over the winter.
"Where it's warm, it's quite warm," said Ken Kunkel, an atmospheric scientist at North Carolina State University. "Very large areas, particularly along the equator, are at record high levels. It's impressive how large those areas are."
Eight of the past 10 months have been the warmest on record, NOAA said. And that's driving the long-term trend relentlessly upward: The coldest month of 2015 topped the warmest month of any year on record before 1990, Dessler said.
"The year-to-year variability is kind of interesting and it makes for good news stories, but what we really like to look at are trends over decades," he said.
"Not every year is going up, and maybe you'll have a decade where the trends aren't very large, like the last decade — but that should give you no comfort," he added.
The last major El Niño peaked in 1998, driving that year's average global temperatures to a record high that stood until 2014. Even when this year's El Niño fades, its effects are likely to linger long enough to boost temperatures well into 2016, Kunkel said. For North America, that's likely to mean a warmer-than-usual winter for the northern latitudes and more wet weather across the southern United States, from drought-stricken California to the already-sodden Southeast.
"It might be that next year would fall short of the records we've set the last two years, but it will start out strong and will probably be well above normal," he said.
Dessler said that's making it harder to argue, as many opponents of climate action have, that there has been no warming since that 1998 peak.
"We are well above the 20th century average now, and we're halfway to 2 degrees Celsius" — the threshold beyond which many scientists warn that warming will likely produce catastrophic effects. "That's sort of the scariest thing."
All four major ocean basins notched record high temperatures during the past 10 months, while on land, only parts of northeastern Canada and the far south of South America were cooler than average.
"Record warmth was observed across the entire southern half of Australia, part of southern and southeastern Asia, much of central and southern Africa, most of Central America and northern South America, and parts of western North America," NOAA reported. "Regionally, Oceania and the African continent were both record warm. Argentina, part of northeastern Canada, scattered regions of western and central Russia, and central Japan were cooler or much cooler than average."
Follow Matt Smith on Twitter: @mattsmithatl