Tag Archives: El Nino

Climate change might be brewing a megadrought in the western US

Warming, shifting climate patterns are likely to push the United States and northern Mexico into extreme, long-term drought.

Image via Pixabay.

The string of dry years that began in the 2000s could be the harbingers of the worst megadrought seen since prehistory, a new study reports. The researchers used modern weather observations and 1,200 years’ worth of tree-ring data to inform dozens of climate models and report that human-caused climate change is at the root of this issue.

Dry, getting dryer

“Earlier studies were largely model projections of the future,” said lead author Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory. “We’re no longer looking at projections, but at where we are now. We now have enough observations of current drought and tree-ring records of past drought to say that we’re on the same trajectory as the worst prehistoric droughts.”

Modern observations can only give us climate data back to about the 1900s, so the team used tree rings to inform their models earlier than that. By analyzing the rate at which these rings grew you can infer conditions such as yearly soil moisture levels throughout time; from that data, broader climate conditions can be determined.

Previous research has tied major, natural droughts with social upheaval in the Medieval area in the American Southwest. The new study expands on that research by offering the most up-to-date and comprehensive long-term analysis covering an area that stretches across nine U.S. states, from Oregon and Montana down through California and New Mexico, and includes part of northern Mexico.

Using tree-ring data, the authors charted dozens of droughts that spread across the region since 800 AD. Four of them, in the late 800s, mid-1100s, the 1200s, and the late 1500s, were dramatic enough to be classed as megadroughts, lasting decades at a time. There were no events of such magnitude recorded after 1600.

Maps of the local rank of the most negative 19-year anomaly to occur during each of the five drought events. Blue indicates no negative 19-year anomaly, while brown indicates the largest anomaly. Numbers in the top left corners indicate the rank of these drought events.
Image credits Park Williams et al., (2020), Science.

Judged from the perspective of soil moisture, the team explains, the period from 2000 to 2018 was the second-driest 19-year increment seen during any drought, only being outdone by the 1575 to 1603 interval — however, the difference between these two is slight and within the margin of error, meaning they could be equally dry. The current drought is also spread more widely and is more consistent than any previous megadrought.

While all those past megadroughts lasted well over 19 years (some even lasted a full century), they all began with trends similar to those showing up now, the team says.

Why now?

Some natural factors, such as El Niño and La Niña, contribute to this incoming drought, but rising temperatures are behind at least half of its severity and pace, the authors argue. Average temperatures since 2000 have risen to 1.2 degrees C (2.2 F) above normal and, because hotter air tends to hold more moisture, that moisture is being pulled from the ground, which further dries out the soil. If this overall warming were subtracted from the equation, the current drought would rank as the 11th worst detected.

“It doesn’t matter if this is exactly the worst drought ever,” said coauthor Benjamin Cook from Lamont and the Goddard Institute for Space Studies. “What matters is that it has been made much worse than it would have been because of climate change.”

As temperatures are expected to keep rising, the drought will likely continue for the foreseeable future or stop briefly only to return, the team concludes. While the team doesn’t predict that the region will become and stay arid, they say that “it is possible”.

“Because the background is getting warmer, the dice are increasingly loaded toward longer and more severe droughts,” said Williams. “We may get lucky, and natural variability will bring more precipitation for a while. But going forward, we’ll need more and more good luck to break out of drought, and less and less bad luck to go back into drought.”

The paper “Large contribution from anthropogenic warming to an emerging North American megadrought” has been published in the journal Science.

Reserachers extracted coral cores in order to tease out information about Earth's past climate. Credit: Jason Turl.

Scientists produce ‘impossible’ 400-year-long record of El Niño events

Reserachers extracted coral cores in order to tease out information about Earth's past climate. Credit: Jason Turl.

Researchers extracted coral cores in order to tease out information about Earth’s past climate. Credit: Jason Turl.

El Niño is a part of a routine climate pattern triggered by anomalously warm ocean water temperatures that periodically develop off the Pacific coast of South America. These seasonal events are extremely important because they cause extreme weather events, particularly in Australia, Southeast Asia, and the Americas. Recently, El Niños have been growing in intensity but scientists weren’t sure how they compare to the past because the instrumental record was too short. But thanks to a breakthrough study, researchers were able to use cores drilled from coral to produce a 400-year-long seasonal record of El Niño events.

Many experts in the field considered it impossible

The study performed by researchers led by Mandy Freund, at the time a doctoral student at the University of Melbourne and the Centre of Excellence for Climate Extremes, used coral cores in order to read variations in climate patterns, similar to how tree rings work. Each layer of coral records growth patterns and contain isotopes that can reveal nitty-gritty details about the climate of the past.

 Dr. Mandy Freund. Credit: University of Melbourne.

Dr. Mandy Freund. Credit: University of Melbourne.

The new record shows a clear trend of intensification of El Niño events. Central Pacific El Niño activity increased over the late 20th-century while Eastern Pacific El Niños are expected to increase in the future. Until recently, scientists were constrained by temperatures records collected by weather stations and satellites, which were too short to put the recent decadal changes into perspective. In the context of climate change, having a record that extends beyond the centuries is extremely valuable.

According to Freund, there has been an unprecedented increase in the number of El Niños forming in the Central Pacific over the past 30 years, compared to all 30 year periods in the past 400 years.

“We are seeing more El Niños forming in the central Pacific Ocean in recent decades, which is unusual across the past 400 years,” Freund said in a statement.

“There are even some early hints that the much stronger Eastern Pacific El Niños, like those that occurred in 1997/98 and 2015/16 may be growing in intensity.”

The El Niño phenomenon is one of the most important features of the global climate, with serious implications for extreme weather events around the world. Thanks to the coral record, researchers will now be better equipped to model, predict, and plan for future El Niños and their potentially devastating impacts.

“By understanding the past, we are better equipped to understand the future, especially in the context of climate change,” said Dr Freund.

“Prior to this research, we did not know how frequently different types of El Niño occurred in past centuries. Now we do,” said co-author from the Centre of Excellence for Climate Extremes Dr Ben Henley.

The findings were reported in the journal Nature Geoscience.

Rainforest canopy.

NASA creates first 3D model of Amazon rainforest canopy to estimate the effects of droughts, climate change

In an effort to estimate the effect of drought on the Brazilian Amazon, NASA has created the first ever 3D model of its canopy.

Rainforest canopy.

Image credits Robert Kerton / CSIRO.

Rainforests are some of the most complex and rich ecosystems on the planet (see here and here). One striking feature of such forests is that their canopies — which can rise up to 15 or even 20 stories high — form ecosystems unto themselves. However, they are in danger.

Climate projections suggest that the Amazon basin will experience warmer and drier conditions in the future. We’ve learned from periods of drought that rainforests don’t handle dryness well. When faced with long periods without rain, rainforest trees risk drying out because there’s not enough water in the soil for them to pump up to the canopies — so they starve.

However, we’re not quite at the point where we can estimate — based on our climate and precipitation projections — exactly how rainforests will react in the future. Simply put, estimating the number of dying or damaged trees (for example, where only branches are falling) is almost impossible. Rainforests are vibrant but chaotic, abundant but densely-packed places, and getting any kind of accurate data on tree health has long been an elusive goal for researchers.

When in doubt, LiDAR the sample

Traditionally, researchers attempted to record this data by hiking through rainforests and surveying a few acres of trees in spots along the way. They would count how many trees were alive, how many were dead, looked at the quantity and types of debris on the ground, and used these readings to estimate forest-wide averages.

Since that has traditionally not-worked-very-well, Doug Morton from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, decided to use an eye in the sky. He and his team used an airplane-mounted light detection and ranging (LiDAR) device to create a 3D model of the Brazilian Amazonian canopy, drawing data from three separate flights in 2013, 2014 and 2016.

LiDAR works largely the same as radar, only it substitutes light in lieu of radio waves. Firing some 300,000 laser pulses a second, LiDAR can provide an incredibly detailed model of an object — much more accurate than what hiking researchers could achieve.

The team flew over two 30-mile (50 km) stretches near the city Santarém in the state of Pará, Brazil: one over the Tapajós National Forest (also in Brazil), and one over privately-owned stretches of the rainforest — most of which are strongly fragmented by human land-use. This region of the Amazon basin typically has a three-month dry season from October through December, the team writes, the same period when surface temperatures peak in the Pacific Ocean (during the El Niño event). El Niño delays the start of the rainy season in the central Amazon, leading to an extended dry season that stresses the trees.

The team used the LiDAR readings to detect gaps in the canopy — areas where a tree or branch had fallen in the months between each survey. They write that between 2013-2014 (a non-El Niño period), falling branches and trees altered around 1.8% of the forest canopy in the examined area. Scaled up over the whole Amazon basin, that would be equivalent to losing canopy trees or branches over 38,000 square miles (98,000 square km).

During the El Niño drought period from 2014 to 2016, branch morality rose by 65%, equivalent to 65,000 square miles (168,000 square km) over the whole basin.

Even subtle changes add up in the Amazon, Morton says, because it’s such a huge forest. So a subtle shift in precipitation patterns during an El Niño year ends up having a huge impact on the forest’s ability to sequester carbon. Dry periods, in other words, alters the balance between how much carbon the trees store as they grow versus how much they give off when they die and decompose.

However, the drought didn’t selectively affect more tall trees than smaller ones, as previous experiments suggest. This, Morton says, is good news.

“Large trees hold most of the carbon in any forest. If droughts were to preferentially kill large trees, it would boost the total amount of carbon that’s lost from drought as opposed to other disturbance types.”

The team says that understanding the effects of prolonged drought will give us a better sense of what might happen to atmospheric carbon levels if drought events become more common due to climate change.

The paper “El Niño drought increased canopy turnover in Amazon forests” has been published in the journal New Phytologist.

3-D cloud and surface temperature data from the Terra satellite show a well-developed El Niño condition. The red area is warm water sitting off the coast of western South America. Credit: NASA

What is El Niño?

3-D cloud and surface temperature data from the Terra satellite show a well-developed El Niño condition. The red area is warm water sitting off the coast of western South America. Credit: NASA

3-D cloud and surface temperature data from the Terra satellite show a well-developed El Niño condition. The red area is warm water sitting off the coast of western South America. Credit: NASA JPL

El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific which impacts weather patterns. It’s also known as the El Niño-Southern Oscillation (ENSO) cycle.

South American fishermen in the 1600s first christened El Niño, which means The Christ Child or The Little Boy, because the oscillation becomes active around Christmas time. Despite the name, no one waits for El Niño like it’s Santa Claus. Along the centuries, ENSO built a reputation as a home wrecker, destroyer of fisheries and even a killer. ENSO severely impacts global weather causing massive amounts of rainfall, powerful gusts of wind, floods or droughts, landslides, cyclones, and typhoons.

El Niño typically occurs in the Pacific but affects weather patterns globally

El-Nino-map-el-nino

Credit: NASA JPL

Since the 1930s, as a result of the pioneering work of Sir Gilbert Walker, climate scientists know El Niño occurs at the same time with the Southern Oscillation, which is a change in air pressure over the tropical Pacific Ocean.

Near the equator, in the Pacific Ocean, the sun shines especially hot and the water at the surface is warmer. Eventually, coastal waters become warm enough to cause the atmospheric pressure above it to decrease. In a normal year, the trade winds blow westward, pushing warm water along the coast of Australian and New Guinea. During an El Nino event, however, strong winds push the warm waters eastward, moving it along the coast of South America until it ultimately pools in Indonesia and the Philippines.

This doesn’t happen all the time, though, since in some years the winds in fall and winter are too weak to move the warm water that far. Instead, the trade winds blow the warm waters towards South America where they split into north towards California and south towards Chile.

In the absence of an El Niño warm currents flow from east to west, due to the planet’s spin around its axis.

El-Nino-map-normal

Credit: NASA JPL

It’s important to note that ENSO is a coupled oscillation which means it can not occur unless interactions between the atmosphere and ocean are in sync. For instance, sometimes atmospheric patterns can shift in the tropical Pacific without the ocean fully responding, and vice versa.

[panel style=”panel-warning” title=”How often El Nino occurs” footer=””]Typically, an El Niño occurs every three to five years during the months of December and January, although it’s not that uncommon for it to happen every two years. ENSO episodes last 9 to 12 months, but some prolonged events may last for up to two years.[/panel]

El Niño effects

How El Nino is affecting areas around the world. Courtesy of NBC News

How El Nino is affecting areas around the world. Courtesy of NBC News

Weather is greatly influenced by the oceans’ surface temperatures. When the ocean is warm, such as during an El Nino, more clouds form leading to more rain. These clouds dump their excess water in South and Central America, as well as in the United States. Rainfall increases drastically in Ecuador and northern Peru, contributing to coastal flooding and erosion.  Meanwhile, at the other end of the world, El Niño can cause droughts in Indonesia and Australia. These droughts threaten the region’s water supplies, as reservoirs dry and rivers carry less water, severely impacting agriculture yield. An El Niño might also trigger odd weather events like making lakes out of deserts overnight or turning rainforests into charcoal.

A severe El Niño event amplifies the western Pacific jet stream and shifts it to the east, which is why in some odd years you’ll see freak winter storms over California and the southern United States, along with floods and landslides.

El Niño lowers the probability of hurricanes forming in the Atlantic but increases the chance of cyclones and typhoons in the Pacific. Strong El Niño events also contribute to weaker monsoons in India Southeast Asia.

The El Niño events of 1982-83 and 1997-98 were the most intense of the 20th century. During the 1982-83 event, sea surface temperatures in the eastern tropical Pacific were 9-18° F above normal and the ensuing onslaught caused $45 billion in damage.

The most recent El Niño, that of winter of 2015, was one of the strongest recorded. Record smashing temperatures hit Thailand, Laos, and Cambodia. In Malaysia, lakes dried up and vegetables withered while weak monsoons and killer heatwaves left India barren.

El Niño forecast

Animated sea surface temperature data. Credit: NASA JPL

Animated sea surface temperature data. Credit: NASA JPL

We don’t currently have the right tools to predict when an El Niño event will happen or how strong it will hit, but we have some pretty good hints. For instance, we know that the oscillation is triggered by changes in pressure and temperature, so these parameters are carefully monitored on a daily basis.

Prior to the 1980s measurements of sea surface temperature were derived from instruments on shorelines, ships, and buoys. Since then, scientists rely on satellite observations because these are more reliable and can cover the whole planet. When the ocean gets warmer, the water expands and sea level rises slightly. The Jason-1 and Jason-2 satellites launched in 2001 and 2008, respectively, are now the go-to instruments for climate scientists because they employ the most sensitive altimeter onboard.

To make things easier, climatologists have developed the Oceanic Nino Index (ONI) whose values correspond to deviations from normal sea temperatures. An El Niño event is forecasted with confidence if sea surface temperatures rise by more than 0.9 degrees Fahrenheit for at least five consecutive three-month seasons. The bigger the temperature deviation, the more powerful the impact El Niño will have on weather and climate. For instance, a weak El Niño raises sea surface temperatures by 4 to 5 degrees F and only moderately affects the world’s climate, but if the temperature rises by 14 to 18 degrees F, the consequences can be very serious.

El Niño flavors

ENSO has various phases called ‘flavors’. For instance, the transitional period at the onset and closing of ENSO is called Trans Niño, and it is usually characterized by intensified tornado activity in the American Midwest. Then there’s the El Niño Modoki, or Modoki Niño, where Modoki is Japanese for “similar, but different”. This flavor is characterized by temperature variations in the central, not eastern, Pacific. Some Modoki events cause increased hurricane activity in the Atlantic and Gulf of Mexico.

 

El Niño is one of the most recognizable climatic events, not least because of the tremendous influence it has on the planet’s weather. There is still a work that needs to be done before we can predict El Niños further out and understand why some effects only show up sometimes. Knowing when and where it will strike will help us prepare for the impacts and make El Niño years less costly to society. 

El Nino, which is Spanish for "the little boy" or "the Christ child," refers to a type of weather pattern which occurs in some years and usually peaks during the winter months of the northern hemisphere.

El Niño shaping up in the Pacific: might be strongest since 1950

According to the World Meteorological Organisation (WMO), there’s now a mature El Niño present in the Pacific Ocean. As is the case with such events, the biggest sign of an El Niño shaping up is rising surface water temperatures. Right now, the east-central tropical Pacific Ocean waters are likely to exceed 2° Celsius above average, which suggests this could be one of the strongest since 1950, placing it along similar events like 1972-73, 1982-83 or 1997-98.

What causes El Niño

El Nino, which is Spanish for "the little boy" or "the Christ child," refers to a type of weather pattern which occurs in some years and usually peaks during the winter months of the northern hemisphere.

El Nino, which is Spanish for “the little boy” or “the Christ child,” refers to a type of weather pattern which occurs in some years and usually peaks during the winter months of the northern hemisphere.

Climate scientists are always on the lookout for an El Niño since the phenomenon influences  how high global temperatures will rise this year, how severe a drought could afflict Australia and Asia, and whether or not rain-starved California will get the precipitation it desperately needs. Most of us, however, know El Niño as a doom bringer leaving floods, droughts, tropical storms and blizzards in its wake. The severity of such an event, of course, depends on where you live. India, Australia and Indonesia are historically hardest hit.

In the absence of an El Niño warm currents flow from east to west, due to the planet’s spin around its axis. In time, winds graze the water absorbing some of the heat and exchanging it further east, in Australia and Asia. At some point, the water in the east gets hot enough that it unbalances the system. As the heat system tries to reach an equilibrium,  warm water starts flowing in reverse from east to west, dragging precipitation with it. As a consequence, some regions of the world will receive excess rain and storms, while others will see little of it.

The event happens every five to eight years, and authorities aren’t exactly looking up for it. This year it’s back.

Once surface water temperatures exceed 1° Celsius above average, the so-called  El Niño threshold is reached. In August  surface temperatures have ranged between +1.3° and +2.0° Celsius which suggests this current   El Niño is already pretty strong. Apart from this, other telltale signs have been identified: patterns of cloudiness and rainfall near and east of the international dateline and weakening of tradewings from the west to east-central Pacific.

This year’s El Niño could be very strong

Here’s a summary of the WMO report:

  • As of August 2015, both the ocean and atmosphere over the tropical Pacific exhibit behaviour indicative of a strong El Niño;
  • A majority of the models surveyed and expert opinion suggest the 2015-16 El Niño will strengthen further during the second half of 2015;
  • The peak strength of this El Niño, expected sometime during October 2015 to January 2016, could potentially place it among the four strongest El Niño events since 1950.
  • Impacts from this El Niño are already evident in some regions and will be more apparent for at least the next 4-8 months;
  • El Niño events typically decline and then dissipate during the first and second quarters of the year following their formation. Note that impacts in some regions are still expected during the dissipation phase.

Another model, this time made by researchers at NOAA’s Climate Prediction Center suggests  there is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016. Across the contiguous United States, temperature and precipitation impacts associated with El Niño are expected to remain minimal during the remainder of the Northern Hemisphere summer and increase into the late fall and winter. El Niño will likely contribute to a below normal Atlantic hurricane season, and to above-normal hurricane seasons in both the central and eastern Pacific hurricane basins. Already, the Western Pacific has seen 5 strong typhoons this year.

Besides the weather, this prince of chaos is also changing fish migratory patterns driving away the coldwater fish – a backbone of the fishing industry in South America. There are of course some upsides to El Niño. For instance, Uruguay gets to have better agricultural conditions. For the most part, though, you don’t want it around.

Who’s most vulnerable

el-nino

The worst El Niño happened in 1997, killing 23,000 people and $45 billion in damage. On the Oceanic Niño Index (ONI) which measures how warm surface waters in the Pacific are (zero is average, positive is warming, negative is cooling), the 1997 event was rated with a 2.3 figure. Right now, the 2015-2016 El Niño event is rated with 1.0 on the ONI scale, however this figure has been constantly rising in the past four months. Models performed by WMO predict it should climb above 2.0 and quite possibly become the strongest since 1950 when such record keeping began.

As mentioned in a previous article in which I explained what drives global warming “hiatus”, the  El Niño also influences climate. At the time, 1998 became the warmest year on record. However, 2014 was the warmest year on record without any El Niño event. Expect 2016 to be very, very hot – another record.

2014 was the hottest year on record. Credit: Leigh Henningham

It’s official: 2014 hottest year on record – all without the help of El Niño

At the beginning of the year, ZME Science reported 2014 was the 18th straight year to have surpassed average 20th-century US temperatures and the warmest year yet, according to the Japanese meteorological agency. Now, both NOAA and NASA have confirmed 2014 to be the warmest on record, despite there was no El Niño event.

2014 was the hottest year on record. Credit:  Leigh Henningham

2014 was the hottest year on record. Credit: Leigh Henningham

El Niño, an abnormal warming of surface ocean waters in the eastern tropical Pacific, is one part of what’s called the Southern Oscillation. The Southern Oscillation is the see-saw pattern of reversing surface air pressure between the eastern and western tropical Pacific; when the surface pressure is high in the eastern tropical Pacific it is low in the western tropical Pacific, and vice-versa. Because the ocean warming and pressure reversals are, for the most part, simultaneous, scientists call this phenomenon the El Nino/Southern Oscillation or ENSO for short. The cool phase of ENSO is called “La Niña” with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific.

What makes El Niño important for the climate is that it raises ocean temperatures, and hence surface temperatures. This happens periodically, and such the event is part of  Earth’s “internal variability”, temporarily shifting heat between the ocean’s surface and depths.  The last five record hot years of 2010, 2005, 1998, 1997, and 1995 were all assisted by El Niño events, yet even though there was no such event in 2014, last year trumped all other years on record as the hottest. As such, 2014 was by far the hottest ENSO-neutral year on record, and the first year since 1990 to set a record without influence from El Niño.The graph below exemplifies.

9a021ccf-4b5c-450f-96fe-7bc987a23510-620x422

Denying the obvious

Climate skeptics will be quick to voice, however, that what we’re currently seeing is a global warming “pause”. Over the past 15 years or so, global surface warming has slowed down a bit. This was enough for skeptics to become convinced that man-made global warming is a hoax, and all the warming we’ve been seeing so far is due to the planet’s inherent variability. What they miss is the big picture. This isn’t the first time warming has halted. In fact there are a number of such periods in recent history, but time and time again temperatures have risen over the decades in steps. That’s because the temporary effect caused by a period with a predominance of La Niña events and other short-term cooling temperature influences. The only thing climate change skeptics get right is this: the planet’s climate is cyclic and thus variable. Yet on top of this natural variability, lies an undeniable and unnatural warming trend. Some skeptics between 1970-1978 told us there was no warming, as those from 1985-1997. Would the same people agree now? No worry, with every cycle there will be people with mixed interests that will be quick to deny global warming is happening, not to mention that there’s any human intervention involved. “We’re just too small.”

climate change denial

“This is the latest in a series of warm years, in a series of warm decades. While the ranking of individual years can be affected by chaotic weather patterns, the long-term trends are attributable to drivers of climate change that right now are dominated by human emissions of greenhouse gases,”  NASA GISS director Gavin Schmidt said,

In 2015, an El Nino event is expected. It seems like 2014 will be a short-lived record holder.

El Nino likely to develop this year – Australian scientists estimate 70% chances

The scientists from the Australian Meteorology Bureau estimate that there’s a good chance that El Nino will form in the southern hemisphere’s winter (northern hemisphere’s summer).

El Nino shaping up in 1997.Via NASA.

El Nino is  a band of anomalously warm ocean water temperatures that periodically develop off the Pacific coast of South America. The results of this pattern are extreme weather events, floods, droughts, etc. When it does form, it has a devastating effect on agriculture, having the most impact on developing countries which greatly rely on agriculture and fishing.

“Although the El Niño–Southern Oscillation (ENSO) is currently neutral, surface and sub-surface ocean temperatures have warmed considerably in recent weeks, consistent with a state of rapid transition.”,said the Australian MeteorologyBureau.

Their climate models forecast a continuous warming in the central Pacific in the upcoming months, and it’s very likely that temperatures will reach El Nino thresholds during the winter season (for the southern hemisphere).

The strength of an El Niño does not always indicate how much it will influence rainfall and how much it will be associated with extreme events. There are examples when weak events have led to massive droughts in some areas and massive rainfalls in others, and the same can be said for the opposite. t is too early to determine the strength of this potential El Nino.

The effects also vary from continent to continent. In South America, the effects typically include massive thunderstorms, increased rainfall, and sometimes strong winds. In North America the effects are similar, but much smaller in amplitude.

Via Australian Meteorology Bureau.

The El Niño turns out to be more chaotic than previously thought

Why would the El Niño be important for the rest of us that don’t live in the western part of South America? Well because it also influences the climate in North America, Asia, Australia, Africa, even Europe perhaps.. so that basically means the whole world. The El Niño-the southern oscillation or ENSO is a sort of a heartbeat of the Earth’s climate, that contains a warm phase (the El Niño) and a cold phase (La Niña). And just like the pulsations of a heart, it’s beats are not monotonous, it is a bit different with every pulsation: some of them are more spread apart than others, some are stronger, some weaker.

A new study that looks at the last 7000 years of El Niño-s finds that this pattern is even more chaotic than scientists previously believed: “This will be a shock for many paleoclimatologists,” says Axel Timmermann, a climate scientist at the University of Hawaii, Manoa, in Honolulu who wasn’t involved in the new research. “[These findings] are a stark contrast to their ideas.”

Divers taking a coral core sample. [Via eurekalert.org]

Divers taking a coral core sample.           [Via eurekalert.org]

In order to get an insight into the past variability of the El Niño, scientists are using climate archives such as lake sediments, tree rings from South America or corals from that specific region in the Pacific that is affected by the Southern Oscillation. The study’s lead author, Kim Cobb, a paleoclimatologist at the Georgia Institute of Technology in Atlanta says that they chose the coral archives in their study due to the fact that they allow a decoding of the variations in both temperature and precipitation on a month-by-month basis. This makes the corals a much better archive in terms of their temporal resolution when compared to the other climate archives.

The team chose to study the variations in the oxygen-18 and oxygen-16 ratio from 17 coral samples taken from Christmas Island and Fanning Island, which are both part of the Line Islands archipelago in the central Pacific. That area of the Pacific experiences higher than average values both in precipitation and temperature in an El Niño period, and due to this increased sensibility, according to Timmermann, it “makes the region a ‘sweet spot’ for climate reconstructions.” By analyzing these coral samples, the team gained access to the climate variability of the last 7000 years in that region of the Central Pacific – an archive that according to Kim Cobb, almost triples the amount of data previously available.

It turns out that long-term variations in the magnitude and frequency of ENSO events during the 20th century were larger on average than any other period in the last 7 millennia. As Kim Cobb says, there have been however, shorter intervals, especially in the 1600s when the El Niño variability was even stronger than in the last century. The relationship between higher ENSO variability and higher CO2 concentrations is very probable but cannot be proven yet due to the insufficient climate data now available.

Coral core sample. Credit: Gary Meek/Georgia Tech

The warm conditions seen in the El Niño of 1997. [Via wikipedia]

The study is important for questioning the notion that the ENSO variability would be related to the amount of solar radiation received by the Northern Hemisphere during the summer – the summer insolation. Previous studies hinted towards a climate trend with a minimum of ENSO variability about 6000 years ago that would have been caused by that gradual variation in summer insolation, but the data in the current study deny the existence of such a trend, or that any influences from the summer insolation would be minimal.

“This [study] shows that ENSO is very variable, all over the map, and overturns the idea that ENSO was weaker during the mid-Holocene [about 6000 years ago],” says Julien Emile-Geay, a climate scientist at the University of Southern California in Los Angeles. This being said, it is too early to say weather the ENSO is inherently chaotic and completely separated from other climate forcing factors, the team says.

Timmermann says that maybe in the next 10 years there will be more data that will fill in the gaps of El Niño related climate archives that will also help to decode what factors if any, influence the mysterious ENSO, and by doing so, the regional and global climatic computer models will also be improved.