In the coming weeks, separate teams of scientists in the United States, Britain, and Japan are expected to announce that 2015 was the warmest year on record. Although their number-crunching is still under wraps, there’s little doubt that last year’s global heat was unprecedented.
That’s partly because of the pulsating red streak across the eastern tropical Pacific shown in the video above. You’re looking at the growth of an El Niño — the warm phase of a natural ocean cycle that disrupts normal weather conditions across the Pacific and beyond.
And not just any El Niño. The current event, which may last until May, is already tied for the strongest ever, and over the next few months may well exceed the intensity of the monster El Niño of 1997-98, which saw Southeast Asia’s forests go up in smoke and beset California with floods and landslides.
Indonesian forests are ablaze again, and El Niño is being blamed for freak weather conditions as far afield as the U.K., hit in recent weeks by heavy floods. Its effects are global, as warm water from the western Pacific sloshes to the east — and, crucially, reaches the surface.
“The tropical Pacific Ocean stores a lot of heat that is buried underneath the ocean surface,” Michael Mann, a climatologist at Pennsylvania State University, told BuzzFeed News by email. “During an El Niño event, much of that heat reaches the surface and warms the atmosphere.”
Global air circulation then spreads the heat around. Right now, this means the planet’s average temperature is about 0.2 degrees Celsius higher than it would otherwise be, Kevin Trenberth, a climatologist at the National Center for Atmospheric Research in Boulder, Colorado, told BuzzFeed News.
The current El Niño only began to build toward a crescendo in the second half of last year. So averaged over the whole of 2015, Trenberth estimates that El Niño will have boosted the global temperature by between 0.1 and 0.15 degrees C above normal.
But “normal” is a moving target, driven by the long-term trend of global warming.
Blue shows years that were cooler than the 20th-century average; red, years that were warmer than this baseline.
The previous record year, 2014, was 0.74 degrees C warmer than the 20th-century average. And data from the U.S. National Oceanic and Atmospheric Administration, complete to the end of November, shows that monthly temperatures in 2015 were averaging 0.87 degrees C above the last century’s baseline.
So by some simple arithmetic from Trenberth’s estimates, 2015 would have been close to matching 2014 even without El Niño. The Pacific Ocean phenomenon simply provided the final push to remove any doubt that 2015 would go down in the record books.
Here are the two most recent years, plus 1998, the last year in which El Niño gave a similar boost to the average global temperature.
From this chart, it’s clear why scientists are so sure that 2015 will set a new record. The El Niño year of 1998 looks chilly in comparison. But at the time, it was the hottest on record — indeed, the slightly cooler years that followed were seized upon by some opponents of the scientific consensus on climate as evidence that global warming had halted.
No such luck. Add just a few years of steady warming to the picture, and 1998 seems nothing special — in addition to the last two years, 2005, 2010 and 2013 were all warmer than the most recent El Niño-assisted record.
If El Niño can warm the planet, will global warming change El Niño?
That’s less clear, but a team led by Wenju Cai of CSIRO Oceans and Atmosphere in Melbourne, Australia, has run climate models suggesting that extreme El Niños, like the current one and the event of 1997-98, will become more common.
As the planet as a whole warms, Cai told BuzzFeed News, climate models suggest that the eastern Pacific is likely to warm faster than the western part of the ocean, making it easier for the system to tip over into El Niño.
If the world’s nations do nothing to halt the rise in greenhouse gas emissions, Cai’s computer simulations indicate that similarly powerful El Niños will by the end of this century come round every 10 years or so, rather than roughly every two decades.
But it’s hard to tell whether we’re already starting to see any change in the pattern of El Niño and its cool counterpart, known as La Niña, because the cycles are irregular, and occur on a timescale of several years.
“It’s very reasonable, but not yet cast in stone,” David Neelin, a climatologist at the University of California, Los Angeles, told BuzzFeed News.
Whether or not powerful El Niños become more common, Mann argues that superimposing the phenomenon over an already warm eastern Pacific is likely to cause increasingly severe disruption.
“This is part of why we are seeing such unprecedented weather extremes here and around the world right now,” Mann said.
Not so much El Niño, perhaps, as El Hombre.
Peter Aldhous is a Science Reporter for BuzzFeed News and is based in San Francisco. His secure PGP fingerprint is 225F B2AF 4B8E 6E3D B1EA 7F9A B96E BF7D 9CB2 9B16
Contact Peter Aldhous at firstname.lastname@example.org.
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