As human activity warms the earth, El Niņo grows more violent. Are we doing this to ourselves?
by Patrick Mazza
"Acts of God" are what people call
the calamities the world suffered at the hands of El Niņo last winter. Freak tornadoes
killed more than three dozen people in Florida. Thirty-five-foot waves battered the
California coast, while a numbing procession of torrential rains brought widespread
flooding and mud slides, driving hundreds of people from their homes and causing up to $1
billion in damage. Hundreds more were killed in Peru and Ecuador by floods and slides, and
thousands left homeless.
Canada and the northeastern United States were hit by a
catastrophic ice storm, which knocked out power to 4 million people. Brazil and Indonesia,
on the other hand, are tinder dry; 12 million acres of their precious rainforest burned
last year. "This was the year the world caught fire," concluded a report by the
World Wildlife Fund.
But it may not be fair to blame these disasters on the Deity. We now know that human
activitymostly the burning of fossil fuelsis warming the earth. The
Intergovernmental Panel on Climate Change, a gathering of 2,000 of the world's top
climatologists, has declared that "the balance of evidence suggests a discernible
human influence on global climate."
How will that influence manifest itself? Warmer air temperatures, ironically, may
ultimately not be the most significant aspect of global warming. According to the U.S.
Global Change Research Program, "Widespread increases in the intensity of the
hydrologic cycle may have more immediate and far-reaching ecological and socioeconomic
impacts than elevated temperature alone."
And one of the most intense manifestations of that hydrologic cycle is the weather
pattern known as El Niņo. Every four to seven years, a band of water 2 to 10 degrees
warmer than the surrounding ocean bulges toward the Pacific coast of South America,
spawning enormous storms, altering currents, changing wind patterns, and causing droughts
all around the world. Because it often appears around Christmas, it's called El Niņo,
The system that arrived in March 1997 came only two years after a five-year El Niņo,
the longest ever documented. The new system gathered power at record speed until its force
exceeded that of 1982/83, previously the most powerful El Niņo on record. With the
ocean's heat valve shifting into overdrive at the same time the planet is experiencing the
warmest year on record, we naturally have to ask: Have we brought this on ourselves? Are
we parents to The Child?
Typically, El Niņo is followed by its cooling counterpart, La Niņa. But over the past
two decades a hothouse Pacific has generated five El Niņos, and only one La Niņa of any
size. "You can think of El Niņo and La Niņa as the ticktock," notes University
of Washington climate-ocean scientist Richard Gammon. "Lately we've been having more
ticks than tocks."
Meteorologists call this ticktock the El Niņo Southern Oscillation, or ENSO. Pioneer
El Niņo researcher Kevin Trenberth was the first to nail down ENSO's four- to seven-year
cycle; he is now trying to determine whether there is a connection between the
unprecedented string of El Niņos since 1976 and the fact that they coincided with the ten
hottest years on record. As the head of the climate analysis section at the National
Center for Atmospheric Research, Trenberth and fellow NCAR scientist Timothy Hoar have
applied statistical methods to the seeming skew in the cycle over the past 20 years. They
concluded that such an odd sequence would occur naturally only once every 2,000 years.
"Is this pattern of change a manifestation of global warming [or] a natural
variation?" Trenberth and Hoar wrote in the peer-reviewed Geophysical Research
Letters. "We have shown that the latter is highly unlikely."
"Something is going on," Trenberth says. "I think El Niņos are being
changed by global warming."
Some scientists have found Trenberth's conclusions less persuasive because El Niņo has
been statistically tracked for only the past 120 years. Even so, Trenberth points out,
"If you take the first 20 years and compare it with the second 20 years, and the
third, fourth, and fifth, they don't look greatly at odds with one another. It's only in
the last 20 years that things seem to have been different."
Attempting to lengthen the historical record, Oregon State University oceanographers
William Quinn and Victor Neal have studied anecdotal accounts by Spanish explorers and
colonists. Doing so has allowed them to tally eight very strong ENSOs from 1525 to 1982.
Since 1728 very strong ENSOs appeared about every 42 years; before that, only one was
detected. Quinn and Neal concluded that the 1982/83 event was the most powerful in nearly
500 years. The 1997/98 El Niņo, apparently even stronger, followed only 14 years
laterthe briefest time between very strong El Niņos, they say, in five centuries.
Ice cores provide physical evidence of climate change in the same period. This data
stretches back thousands of years, notes Nicholas Graham, a climate-ocean researcher at
Scripps Oceanographic Laboratory, but recent warm temperatures have melted away the
evidence of the past several decades. "This suggests very strongly that the
temperatures in the mid-nineteen seventies to early nineties were the warmest in the last
five hundred years."
According to the IPCC, global warming has raised world ocean temperatures by one degree
in the past century. The world's warmest patch of ocean is the tropical Pacific; when its
heat reservoir fills to the brim, El Niņo acts as the discharge valve. "The climate
system is a giant heat engine," explains Nathan Mantua, a climate researcher at the
University of Washington who focuses on the Pacific. "An excess of energy comes in at
low latitudes relative to the high latitudes; winds and currents try to wipe out this
imbalance." The workings of this engine shape the earth's standard weather patterns.
The most prominent effect of solar energy striking the earth is not to heat the atmosphere
but to evaporate water from the surface of the ocean. The warm, moist air rises to form
clouds, where water condenses and falls back as cooling rain. The heat that evaporated the
water continues to ascend, and is carried for thousands of miles by high winds.
The tropical western Pacific is the hottest stretch of open ocean on
Earth"the warm pool," scientists call it. In normal years, heat rises from
the region, creating a low pressure zone. Rising in the atmosphere, it blows east until it
descends off the coast of South America, creating a high pressure zone. In an effort to
achieve equilibrium, the atmosphere pumps surface winds west along the equator back toward
the warm poolthe famous trade winds. The winds push warm water west, allowing cool
water to rise to the surface in the east. This upwelling of nutrient-rich water is crucial
to South American fisheries; though upwelling areas cover only one-tenth of one percent of
the earth's oceans, they account for 40 percent of the commercial fish catch.
This normal cycle, however, cannot dissipate all the excess heat in the tropical
Pacific. When too much accumulates, El Niņo kicks in. The warm pool's system of clouds
and heavy rainfall expands toward the central Pacific, blunting the trade winds.
Consequently, the warm water piled up in the western Pacific rushes east until it hits the
coast of South America, blocking the cool upwelling and collapsing fisheries.
In addition to disrupting the trade winds, El Niņo's storm track is powerful enough to
divide the jet stream, which normally courses over the Pacific Northwest. During El Niņo
one branch blows farther north, while the other is drawn south across vast expanses of
heat-pumping warm ocean, where it picks up abnormally large amounts of water. In North
America, this leaves the Northwest warmer and drier, California and the Southwest sodden
and cooler. The storms that walloped California grew strong on El Niņo's heated waters,
and the powerful southern branch of the jet stream energized a low-pressure zone in the
Southeast, giving rise to Florida's killer tornadoes.
While El Niņo blows cold and wet in California, it causes drought in India, Southeast
Asia, Brazil, and parts of Africa. Besides devastating agriculture, the disruption of
normal rain patterns sets the stage for huge fires such as those last year in Australia,
Indonesia, and Amazonia. Should El Niņo conditions persist, entire regions could see
their natural features radically altered and economies shaken to their root.
A rule of thumb is that every 2 degree increase in temperature puts 6 percent more
water vapor into the air. And according to the U.S. Global Change Research Program, more
water vapor in the atmosphere means "a significant increase in the energy available
to drive storms and associated weather fronts."
From 1973 to 1993, notes Trenberth, atmospheric moisture over the United States
increased by 5 percent per decade. In 1995 the National Climatic Data Center found that
precipitation over temperate regions of the Northern Hemisphere had increased 10 percent
over the past century, while extreme rain and snowstorms have gone up 20 percent.
Other studies have connected warmer tropical oceans with the retreat of mountain
glaciers around the world. (At the current rate of retreat, there will be no glaciers left
in Glacier National Park in 30 years.) The National Oceanic and Atmospheric
Administration's Climate Diagnostics Center reports that its research "strongly
suggests that the recent observed changes in freezing-level heights are related to a
long-term increase in sea surface temperature in the Tropics."
If global warming continues, El Niņolike weather may become the norm. A computer
simulation run by Gerald Meehl and Warren Washington of NCAR shows El Niņolike
conditions persisting as greenhouse gases increase. With a doubling of the amount of
carbon dioxide in the atmosphere, their model shows trade winds slackening while the
eastern Pacific warms, increasing rainfall and kicking on the heat machine. And, Meehl
warns, should El Niņo become the norm, global warming might also ratchet up the ENSO
cycle to an even more intense level.
Washington and other researchers caution that science is far from a consensus on the
relationship between ENSO and global warming. While El Niņos and ocean temperatures
"are increasing in a way...consistent with the idea that climate change is making El
Niņo more intense," says Nathan Mantua, "it's not quite a bulletproof statement
at this time."
The scientific method demands not only that theory be backed by solid evidence, but
that the evidence hold up under repeated experiments. For climate scientists, those
experiments are conducted using computer simulations. While some models show an
ENSOclimate change connection, many do not. In fact, the first success in predicting
El Niņo didn't come until 1986. A number of models accurately forecast the next ENSO in
1991, but of seven major models, not one predicted the extreme magnitude of the 1997/98
"Computer models used for global climate change don't do a great job of simulating
natural variability," Mantua notes. "The models that do, don't do a good job on
global climate change." Part of the difficulty is that studies of El Niņo and global
warming are, for the most part, taking place in separate scientific venues. "The El
Niņo people are really meteorologists who work in forecasts out from two weeks to a month
to a season," says Richard Gammon. "The climate people are coming at it from a
much longer perspective. There's not enough communication between those two groups. Most
scientists are in their own very small corner of the sandbox."
Public policy should not necessarily wait for scientific consensus, however. "The
level of proof scientists need is much higher than what you would think is important in
public policy," says Gammon. "If you knew with even seventy percent certainty
that something bad was going to happen, as a civil servant you would ring the bell."
If humans are indeed influencing El Niņo, it brings the disruptive potential of global
warming into immediate focus. Our response, says Trenberth, comes down to a value
judgment: "How much we pay attention to the future generations and what kind of
stewards we are to the planet."
What You Can Do To Curb Global Warming
It's not too late to slow global warming and the
violent weather changes that come with it. The single biggest step we can take to stop
climate change is to raise the fuel-economy standards for cars and light trucks. You can
lobby for these changes by mailing a photo of your children or grandchildren to The White
House, 1600 Pennsylvania Ave. N.W., Washington, DC 20500, along with a note asking the
president to guarantee their future by raising fuel-efficiency standards.
While you're at
it, make the same request by writing, faxing, phoning, or e-mailing your senators and
representative. Also ask them to support President Clinton's green tax incentives to cut
global-warming pollution. These tax proposals will help consumers buy clean cars and more
energy-efficient homes, and will promote the technology we need to curb global warming.
can also take personal steps to reduce greenhouse gases:
Buy the most efficient vehicle that suits your needs. Avoid sport utility
vehicles, pickups, and minivans, and aim for a vehicle that gets at least 35 miles per
Drive smart. Combine trips, and carpool when you can. Better yet, take public
transit, bicycle, or walk.
Be efficient. Use compact fluorescent lightbulbs. When you replace appliances,
look for those that carry the EPA's "Energy Star" logo. Paul Rauber
Patrick Mazza edits Cascadia Planet, a Pacific Northwest bioregional Web site at
www.tnews.com. A longer version of this article, "El Niņo's Growing Ferocity: Ocean
in the Greenhouse?" is available from the Atmosphere Alliance, 2103 Harrison Ave.
N.W., Suite 2615, Olympia, WA 98502; (360) 352-1763; e-mail firstname.lastname@example.org.