NOAA Elevated ocean surface temperatures in the eastern Pacific Ocean are a sign of El Niño.
Nature | News: Explainer
Event could bring rain to drought-stricken California and dry conditions to Australia.
The El Niño weather pattern developing in the Pacific Ocean could eventually rank among the strongest on record, forecasters with the US National Oceanic and Atmospheric Administration (NOAA) said on 13 August. A strong El Niño — signalled by the periodic warming of ocean-surface temperatures in the equatorial Pacific — can lead to heavy rain in parts of North America and drier-than-normal conditions in Australia, Indonesia and parts of India. NOAA says that there is an 85% chance that the current El Niño will last through the first few months of next year, with its strength peaking in November or December. Nature explains why this El Niño is unusual, and how it might affect weather around the world.
How does an El Niño form?
The weather pattern is the product of a complex dance between sea-surface temperatures and atmospheric conditions. Normally, trade winds from the east drive cold water from the depths of the eastern Pacific Ocean to the surface. But sometimes those winds weaken, causing the ocean surface to warm and heat the air above it. That warm air rises, and moves north and south from the equator — altering the high-altitude air currents along which storms tend to travel.
How do scientists forecast an El Niño?
Forecasters in the United States, Japan and Australia monitor sea-surface temperatures in the Pacific, paying particular attention to a region called Niño 3.4 in the eastern equatorial Pacific. They also track water temperatures below the ocean surface and the air pressure above, then feed this information into forecast models. If ocean-surface temperatures in the Niño-3.4 region are between 0.5 to 1 °C above average during a three-month window, NOAA declares a weak El Niño. Forecasters label an El Niño as strong if it exceeds the average by 1.5 °C. NOAA projects that the current event could produce temperatures that are 2 °C higher than average, or more. For comparison, the strongest El Niño on record occurred in 1997–98 and produced temperatures 2.3 °C above average.
What makes this El Niño different?
Two things. It started unusually early — in March instead of June. This could be because warm waters left over from last year’s weak El Niño gave it a head start, says Anthony Barnston, chief forecaster at the International Research Institute for Climate and Society at Columbia University in Palisades, New York. And this would be the second El Niño year in a row, following the weak El Niño that developed late last year, Barnston adds. A similar El Niño double-header happened between 1986 and 1988, but forecasters predict that the current El Niño will become stronger than either of those two events.
Could this end the drought in California?
El Niño could offer some relief to the US state, which is now in the fourth year of a historic drought. Forecasters say that there is a good chance that southern California will receive more rainfall than usual throughout the winter. In the past, very strong El Niños have also soaked the central and northern parts of the state. Still, “one season of above-normal rain and snow is very unlikely to erase four years of drought”, says Mike Halpert, deputy director of NOAA’s Climate Prediction Center in College Park, Maryland. According to a study published last month in the Journal of Geophysical Research: Atmospheres1, California’s rain shortfall since the start of the current drought is roughly equal to the amount of rain the state would receive in a normal year.
What effects might El Niño have elsewhere?
El Niño is associated with higher atmospheric pressure in the western Pacific, which tends to produce sunny, dry weather in parts of Australia and Indonesia, says Barnston. The effects can spread all the way to India, which has experienced a relatively dry June and July. “They’re having a bad monsoon in India,” Barnston says. In Peru, where waters off the coast typically warm during El Niño, the government has declared a state of emergency because of concerns about heavy rain and mudslides.
Nature Climate Change 5, 787 (2015) doi:10.1038/nclimate2790 Editorial Published online 17 August 2015
After a false start in 2014, this year is shaping up to host a strong El Niño event. The question is why were last year’s predictions of the natural phenomenon wrong? And what is the state of knowledge on the El Niño/Southern Oscillation (ENSO)? All systems are go, with the much-anticipated El Niño event underway. The National Oceanic and Atmospheric Administration (NOAA) forecast a >90% chance of the event continuing through the Northern Hemisphere winter and a strong chance (~80%) of continuing into the start of 20161. The strength of the event is unknown and after the failure to forecast last year (discussed in a Commentary by McPhaden2), there may be some reluctance to make strong statements. That doesn’t mean that all are shying away, a NASA climatologist is reported to have stated that a “Godzilla” event will happen3, with 1997/1998 being the last event worthy of this status….
…The El Niño phenomenon has been known for many years, but how much do we understand this natural variability of the climate system? In a web focus this month, ENSO Under Change (http://www.nature.com/nclimate/focus/enso-under-change/index.html), we present a collection of pieces alongside a selection from the archives of Nature Climate Change, Nature, Nature Geoscience and Nature Communications. This body of work investigates how climate change is impacting on ENSO, and more specifically how it is affecting the severity and frequency of extreme ENSO events8. Although many people are familiar (particularly those who reside in countries affected) with the hydrological changes associated with the ENSO phenomenon, there are other, less-known effects. One of these is increases in cyclone intensity in the western Pacific9. The increase is thought to result from a shift in the location where the storms form — warm central Pacific waters. The shift away from land means the storms have more time in open water to gain strength before making landfall. Climate change is thought to play a role in storm frequency, with increased intensity storms expected. This could result in devastation of the communities in their path, although overall storm occurrence may decrease10. A sobering thought, as (at the time of writing) another storm, Typhoon Soudelor, is ramping up in the Western Pacific Ocean. Scientists are working towards understanding the dynamics at play in the Pacific Ocean, but as the climate changes we don’t have a stable baseline for comparisons. So let’s just consider what is happening now — current information (such as the SST anomalies shown above, which tell only a small part of the story) is that a strong event is underway. The impacts on communities is difficult to predict and only time will tell how extreme the event will become. If anything, the last year and the false start have just reminded us that we still have a lot to learn about this planet of ours.
by Joe Romm Aug 17, 2015 8:00am
NASA oceanographer Bill Patzert called the intensifying El Niño, “Godzilla.” A NOAA research scientist called it “Bruce Lee” in July, and, by August, she said that what’s coming is “Supercalifragilisticexpealidocious.” Whatever you call it, the short-term burst of regional warming in the tropical Pacific (from the monster El Niño) combined with the strong underlying long-term global warming trend means that 2015 will easily be the hottest year on record — blowing past the record just set in 2014. And if the global temperature pattern repeats that of the last super El Niño (1997-1998), then 2016 could well top 2015 record. Here’s why. First, as a 2010 NASA study explained, the 12-month running mean global temperature tends to lag the temperature in the key Niño 3.4 region of the equatorial Pacific “by 4 months.” El Niño (and La Niña) are typically defined as positive (and negative) sustained sea surface temperature anomalies greater than 0.5°C across the central tropical Pacific Ocean’s Nino 3.4 region. More details here.
Second, in its monthly ENSO (El Niño Southern Oscillation) update released last week, NOAA reported, “All multi-model averages predict a strong event at its peak in late fall/early winter.” NOAA’s National Centers for Environmental Prediction (NCEP) went on to explain, “At this time, the forecaster consensus unanimously favors a strong El Niño, with peak 3-month SST departures in the Niño 3.4 region potentially near or exceeding +2.0°C.”……. Climatologist Kevin Trenberth has explained that “a global temperature increase occurs in the latter stages of an El Niño event, as heat comes out of the ocean and warms the atmosphere.” Over 90 percent of global heating goes into the oceans — and ocean warming has sped up recently. Trenberth has been expecting a jump of up to half a degree Fahrenheit, which could occur “relatively abruptly.” He told ClimateProgress back in April that it’s significant the Pacific Decadal Oscillation (PDO) “seems to have gone strongly positive” because that is “perhaps the best single indicator to me that a jump is imminent. The PDO is a “pattern of Pacific climate variability similar to ENSO in character, but which varies over a much longer time scale.” The PDO can remain in one phase almost exclusively for a decade or even longer, as this figure from NOAA’s August “Global Ocean Monitoring” report shows:
“Positive PDO has persisted 13 months since July 2014 and PDO index =1.5 in July 2015.” Via NOAA
Now compare the PDO chart with this NASA global temp chart update to include the record temperatures from July:
You can see that a negative PDO temporarily offsets the long-term global warming trend, whereas a positive PDO brings a “catch up” phase (see discussion here). That is one reason, Trenberth explains, that global temperatures seem to look more like a staircase than a ramp (a steadily-rising straight-line or linear trend).
The last time global temperatures jumped sharply, it was during an extended period of positive PDO, from 1992 and 1998, ending in the monster El Niño of 1997-1998, which set a new global temperature record by a wide margin. That became a high bar for later years to match, which cherry-picking climate science deniers used — with some success — to persuade conservative politicians and media outlets that global warming had paused or slowed down. In fact we have merely been in an extended period of the PDO negative phase, with only occasional switches to a mild positive phase. And that, coupled with some recent La Niñas, gave an appearance of a short-term slowdown in warming in some datasets. But the NASA chart highlights the fact there has been no actual slowdown in warming. Indeed the March study, “Near-term acceleration in the rate of temperature change” makes clear the only “pause” there has been was in the long-expected speed-up of global warming. The rate of surface warming should have started to accelerate in the past decade, rather than stay fairly constant. The authors warned that, by 2020, human-caused warming will move the Earth’s climate system into a regime of rapid multi-decadal rates of warming — with Arctic warming rising a stunning 1°F per decade by the 2020s. They project that within the next few years, “there is an increased likelihood of accelerated global warming associated with release of heat from the sub-surface ocean and a reversal of the phase of decadal variability in the Pacific Ocean.” That accelerated warming appears to starting now.
How This El Niño Is And Isn’t Like 1997
Posted on 7 August 2015 – a re-post from Climate Central by Andrea Thompson
It was the winter of 1997-1998 when the granddaddy of El Niños — the one by which all other El Niños are judged — vaulted the climate term to household name status. It had such a noticeable impact on U.S. weather that it appeared everywhere from news coverage of mudslides in Southern California to Chris Farley’s legendary sketch on “Saturday Night Live.” Basically, it was the “polar vortex” of the late ’90s. So it’s no wonder that it is the touchstone event that people think of when they hear that name. And naturally, as the current El Niño event has gained steam, the comparisons to 1997 have been increasingly bandied about. The most recent came this week in the form of an image from the National Oceanic and Atmospheric Administration that compares satellite shots of warm Pacific Ocean waters — a hallmark of El Niño — from this June to November 1997, when that El Niño hit its peak. On the one hand, the two are comparable given that 1997 was the strongest El Niño on record and, at the moment, the best science indicates that the current event could match or rival that one — at least in terms of ocean temperatures. But on the other hand, each El Niño event is its own beast, the product of conditions in the ocean and atmosphere, of climate and weather that are unique in that particular place and time. In the, albeit very short, modern record of El Niños, “we cannot find a single El Niño event that tracked like another El Niño event,” Michelle L’Heureux, a forecaster with NOAA’s Climate Prediction Center, said. Forecasters like L’Heureux cringe at comparisons because there’s no guarantee the impacts of one El Niño will be just like that of a previous one, even if they look broadly similar. And it’s those impacts — like potential rains in drought-stricken California — that most really care about.
El Niño is not, as Farley’s sketch had it, an individual storm, like a hurricane. Rather it is a shift in the background state of the climate brought about by the sloshing of warm ocean water from its normal home in the western tropical Pacific over to the east. That redistribution affects how and where ocean heat is emitted into the atmosphere, which can alter the normal patterns of winds and stormy weather in the region.
Those more local shifts can telegraph through the atmosphere and, in the case of the U.S., can alter the position of the jet stream over the country during the winter months, typically leading to wetter-than-normal conditions over the southern tier of states and warmer temperatures over the north. Those are the effects of El Niño very broadly speaking, though. Such teleconnections, as they are called, tend to be more reliable when the El Niño is a strong one.
Such was the case with both the strong events of 1997-1998 and 1982-1983. January and February 1998 were the wettest and warmest first two months to a year for the contiguous U.S. in the 104-year record at that time, according to NOAA. The position of the jet stream meant that some northern states saw temperatures up to 15 degrees above normal and both the Southeast and Southern California were awash in a series of storms.
In California, the rains were so unrelenting that they led to mudslides that caused houses to crumble off disintegrating cliffs and racked up hundreds of millions of dollars in damages….With California now five years into a debilitating drought that has led to the first statewide water restrictions in its history, some El Niño-fueled rains (if not the more damaging aspects) may be quite welcome right now.
But here’s the thing: Those two strong El Niños that saw heavy winter rains in California are only that, a sample of two. In science, that’s too small a pool to make any firm conclusions, L’Heureux said.
‘Not the Only Ball Game’
There are other factors, from the inherent chaos of the atmosphere, to other large-scale climate signals, that can potentially override any push provided by El Niño. This is exactly what happened with the El Niño of 2009-2010, which while it wasn’t as strong as 1997, was still significant. But other climate signals helped blunt its effects in the U.S., particularly in terms of temperatures, L’Heureux said. Events like that make forecasters cautious about comparing the current El Niño to 1997. (NOAA acknowledged as much by changing out the original image it used and noting that it did so to avoid confusion). “We think that the strength of [El Niño] is important,” L’Heureux said, but the exact strength it achieves is no guarantee of impacts similar to 1997, “and that’s simply because there’s other stuff going on,” she said. “El Niño is not the only ball game in town.”…. So where does that leave us in terms of looking ahead to what El Niño might bring this winter? We have an event that is looking more and more robust (when comparing June 2015 to June 1997, the broad ocean temperature patterns are very similar) and forecasting models are in pretty good agreement that that event will strengthen as we head towards winter and El Niño’s typical peak. But exactly when it will peak and what its final strength will be is still uncertain. Even more uncertain is what those other influences on U.S. weather will be. So what forecasters can say for now is that the likelihood of those typical El Niño impacts, including rains in Southern California, are higher, but exactly where those rains might fall isn’t yet known. One factor that may influence that is the remarkable pool of very warm waters that has been parked off the West Coast for a couple years now, a feature that was not present back in 1997. That feature could impact the typical changes El Niño brings to the jet stream, Daniel Swain, a PhD student in climate science at Stanford University, said in an email. It is possible that if the El Niño builds up enough strength, it could overcome that influence, though, he added “If El Niño really does make [it] into record territory during the coming winter, it’s hard to envision California not experiencing a wetter-than-average winter, at least to some degree,” he said. The only real guarantee that forecasters can make, though, is that this El Niño event “will evolve in its own way,” L’Heureux said. “It may be similar to certain past events,” but it won’t be exactly the same.
By Eric Holthaus slate.com August 18, 2015
There’s a silver lining to all this talk of a super mega record-breaking Godzilla El Niño: The seasonal weather outlooks for this fall and winter will be some of the most accurate ever issued. Last spring I profiled what El Niño—a periodic warming of the tropical Pacific Ocean—means for 60 places across the globe. Now that the event is in full swing, we have an even better idea of how U.S. weather will be affected over the next nine months. That’s because El Niño acts like a heat engine that bends weather in a predictable pattern worldwide. Typically, the stronger El Niño is, the more predictable its influence. And this year’s event is on pace to be one of the strongest ever recorded. By some measures, it already is. “We’re correct more than the usual proportion of the time when there’s an El Niño,” said Tony Barnston, chief forecaster at the International Research Institute for Climate and Society, in a video statement. Barnston and his team—which actually invented successful El Niño prediction—recently issued an astounding forecast that essentially locks in a strong El Niño through next spring. Globally, it’s now virtually certain that 2015 will be the hottest year in history.
That’s a pretty remarkable thing to be able to say with more than four months of the year remaining. Last week data from NASA and the Japan Meteorological Agency confirmed that last month was the hottest July on record, joining every month so far this year except February and April as the warmest ever measured, according to calculations from Japan. As of mid-August, the Pacific Ocean had configured itself into an unprecedented temperature pattern, with record-setting warm water stretching from the equator all the way northward to Alaska. Thanks to the pattern’s expected persistence, we can already piece together a pretty good guess of the implications—months ahead of time. So, without further ado, Here’s what to expect this winter:
Will California get some drought relief?
To answer everyone’s question, yes, this winter will likely bring above-normal rainfall to California. To answer a related question, no, it won’t end the drought. After a record-breaking four-year stretch, California has racked up a mind-boggling rainfall deficit: San Francisco is more than 31 inches behind—meaning this winter would have to feature a year and a half of extra rainfall during the six-month rainy season to break even. That very likely won’t happen, and even if it did, flooding and mudslides would create an even bigger problem than another year of drought would. What’s more, there’s an especially big caveat this winter. Current temperatures off the West Coast are already far warmer than anything ever measured. The placement of that huge mass of warm water—cutely called “the blob” by local scientists—tends to work against heavy rainfall in California, and it’s a big reason why the drought has been so bad there the last couple of years.
This’ll be an epic battle between dueling masses of warm water (El Niño vs. “the blob”) all winter long on the high seas of the North Pacific (and in the atmosphere above it), but as of now, it looks like California will indeed get some desperately needed rain—enough to matter, just not enough to end the drought….
By Rob Painting Skepticalscience.com August 12, 2015
- A powerful El Niño event continues to strengthen in the Pacific Ocean. During El Niño the poleward transport of warm surface water out of the tropics slows down dramatically and generally results in anomalous short-term heating of the tropical ocean – home to the world’s coral reefs).
- Because of the long-term warming of the oceans by industrial emission of greenhouse gases, the temporary surge in tropical sea surface temperatures associated with El Niño now threatens large-scale coral bleaching episodes – times when the maximum summer water temperatures become so warm that coral die in large numbers.
The powerful El Niño now forming, combined with the ongoing ocean warming, suggests that we are likely to see a mass coral bleaching episode that approaches, or exceeds, the worldwide bleaching that came with the Super El Niño years of 1982/1983 and 1997/1998. The 1997/1998 Super El Niño saw 16% of the world’s coral bleach, the largest die-off ever observed, and some of this coral has never recovered…