Last year nudged its way into the books as the warmest year on record globally, according to preliminary estimates from the National Aeronautics and Space Administration and the National Oceanic and Atmospheric Administration.
Surface temperatures for the year, averaged across the globe, ran 1.22 degrees F. above the 1951-80 average, according to NASA. NOAA puts the figure at 1.24 degrees F. above the 20th-century average.
Either way, the results – echoed in a recent analysis from Japan's Meteorological Agency, which found 1.13 degrees F. above the 20th-century average – indicate that global warming continues unabated, despite a slowdown in the pace of warming during the first part of the 21st century.
"There are going to be periods when short-term trends go up and go down. That's just the nature of the beast," said Gavin Schmidt, director of NASA's Goddard Institute for Space Studies in New York, during a briefing Friday laying out 2014's trends. "But there's no evidence that the long-term trend is really much different from what it has been" over the past 45 years or more.
The numbers for last year are preliminary and carry uncertainties. Even so, NOAA's figures indicate that 2014 is 2.5 times more likely to be the warmest year on record versus any other year on record, while NASA puts the likelihood at 1.5 times that of any other year.
The data will be updated throughout this year, noted Thomas Karl, who heads NOAA's National Climatic Data Center in Asheville, N.C. Based on the updating work already under way, "the picture we're presenting today with respect to record warm temperatures is not going to change," he said during the briefing.
With 2014's newfound status, the 10 warmest years on record all have occurred since 1998. This period includes four previous record-breakers.
But 2014's status may be short-lived. A new informal analysis of current climate conditions, including the state of the tropical Pacific, suggests that 2015 could top 2014 in terms of warming.
That analysis – conducted by former NASA climate scientist James Hansen, Dr. Schmidt, and researchers from Trinnovim LLC and Columbia University's Earth Institute – notes that a chance remains that the tropical Pacific region will finally shift into an El Niño state from its current neutral state.
Throughout last year, various groups predicted a shift to El Niño, which even without global warming generally leads to global average temperatures warmer than normal during the year it pops up. Conditions teetered on the verge of a weak El Niño in November and December. But so far, El Niño has been AWOL.
But even without an El Niño event, it's conceivable that 2015 could top 2014, given that 2014 reached its spot when El Niño played hooky, Schmidt noted during the briefing.
"With the help of even a mild El Niño, 2015 may be significantly warmer than 2014," the team concludes in its analysis.
Not surprisingly, global average temperatures for the year mask significant regional differences. The US heartland experienced a colder-than-normal year, with the average temperature for the year approaching record lows in some areas.
But if the central US shivered, most of the rest of the world would have been happy to share some of that coolness. Land and ocean surface temperatures were above normal to well above normal for most of the planet. Hot spots included a region extending from Canada's Yukon west into eastern Siberia – where annual average temperatures ran as much as 7 degrees F. above normal. Even large swaths of Antarctica registered temperatures up to 5 degrees F. above normal, according to NASA's records.
Above-average warmth also covered much of the US West Coast, where drought seems firmly entrenched. Western Eurasia, northwestern Africa, eastern Eurasia, and Australia also felt the heat.
As for how long the slowdown in warming might last, estimates run the gamut – from "by the end of this decade" to another 20 years, based on the mix of mechanisms driving the slowdown, according to several studies presented at the American Meteorological Society's annual meeting in Phoenix earlier this month.
For his part, Schmidt says he expects the slowdown to speed up sooner rather than later.
The increase in greenhouse gases from burning fossil fuels and from land-use changes "is unrelenting, and that, in the end, is going to dominate most of the other things that are going on" that contribute to the slowdown, he said. "In five or 10 years' time, greenhouse gases dominate those things."