Worrying about El Niņo

By Sallie Baliunas, Ph.D.,
Harvard Smithsonian Center of Astrophysics

The first El Niņo of the 21st Century began unfolding last year, and is partly blamed for warm surface temperatures, floods and droughts. Will El Niņo events intensify or increase in frequency if surface temperatures were to rise from continued human fossil fuel use?

El Niņo is a natural climate phenomenon that appears every few years and persists for several seasons. It is marked by a wide area of warmth in the tropical Pacific. That ocean warmth often spikes up global average surface temperatures.

An intense El Niņo may alter storm patterns to cause drought in some places and floods in others. It may enrich fish populations off Chile, and suppress the formation of Atlantic basin hurricanes, the most costly weather disaster for the U.S.

Thus, while El Niņo is natural and has positive as well as negative effects, the prior event, in 1997-98, led to speculation that human-made global warming from fossil-fuel use would spin world weather into a semi-permanent El Niņo state of weather disasters.

The problem with such fears: No reliable evidence says human actions have affected El Niņo.

What happens during El Niņo?

Across the tropical Pacific the trade winds generally blow from east to west. The motion puddles warm water near Indonesia and Australia, while an undersea current feeds chilly water to the coast of Peru.

During an El Niņo event, the trade winds weaken, the undersea current shifts and warm water, rather than cold, stretches across the western Pacific towards Peru. Because sea surface temperature, undersea currents and air currents shift so dramatically over a large region of the tropical Pacific, weather patterns there and beyond correspondingly shift. For some of those regions, the El Niņo condition may generate serious droughts; other regions may suffer from floods.

There is also an opposite, extreme state of the tropical Pacific, called La Niņa, when colder than usual water pools off Peru. Roughly speaking, La Niņa tends to shift weather patterns oppositely from El Niņo, e.g., where El Niņo had caused a severe drought, La Niņa might cause flooding in the same region. These outcomes are only tendencies because other aspects of the climate affect El Niņo, La Niņa and their influence.

During the 19th century, the recurrence of severe drought followed by famine led researchers to seek patterns, and perhaps predictability, of such weather.

Tracking Monsoons and Famine

Historically, India and China have suffered monsoon failures that caused major famines. Among the most severe, according to the 1911 edition of Encyclopedia Britannica, are:

• Little rain for two years led to a severe famine in India in 1661.
  
• In Bengal, around 10 million people (around one-third its population) died in the 1769-70 famine.
  
• The "skull famine" in 1790-92 killed so many from Bombay to Hyderabad and the Northern Madras Presidency that they could not be buried - about half the population of Northern Madras perished.
  
• In 1869 approximately 1.5 million died in the famine in Rajputana.
  
• Scant rainfall and ensuing famine in India and China in 1876-78 caused 5 million deaths in Bombay, Madras and Mysore while in northern China over 9 million died.

John Eliot in 1894 saw that summer rain in India was related to air pressure near the South Indian Ocean. By the early 20th century, the British mathematician Sir Gilbert Walker had identified a far-reaching periodic shift in barometric pressure at sea level between Tahiti and Darwin, Australia - some 5,300 miles apart - termed the Southern Oscillation.

What this means is that if low air pressure sits over Tahiti, high pressure generally pertains at Darwin, but every several years the pressure pattern shifts. Meteorologist Jacob Bjerknes in 1969 connected Walker's finding on the Southern Oscillation with El Niņo, giving rise to the formal term, El Niņo Southern Oscillation, or ENSO.

According to Australian researcher R.H. Grove, every major drought in India between 1526 and 1900 is related to these El Niņo conditions, when monsoon rains in areas of India were diverted, generating risk of crop failure and famine.

A Global Warming Link?

Modern studies link several weather events across the world to recent El Niņo occurrences. Columbia University researchers list drought in Mexico, Central America, Southern and Northern Africa caused by the 1982-83 El Niņo. Additionally, severe rain fell on coastal California, Western Europe and the Galapagos, where the seal pup population was devastated. Worldwide property damage was estimated at $10.5 billion, and more than 2,000 people perished.

Similarly, the 1997-98 El Niņo caused destructive weather and death. Strong drought prevailed in Australia. Extreme rainfall and floods in 1997 in Uganda led to more than 50,000 cases of cholera and 2,000 deaths there, according to Center for Disease Control.

Further, the mild U.S. winter of the 1997-98 El Niņo pushed that natural phenomenon into the human-made global warming debate. Specifically, would anthropogenic warming cause more intense or frequent or both El Niņo-spawned severe weather?

The White House in 1998 issued a statement that linked the warming from that year's El Niņo to extreme weather disasters. The statement speculated that more such disasters would occur in a world warmed by human made greenhouse gas emissions unless emissions were cut, according to a June 8, 1998 story in The New York Times.

Paleoclimate, geological and archaeological evidence suggests otherwise., El Niņo occurrence may weaken or become less frequent during warm periods. That happened approximately 6,000 years ago for several millennia during the warmest period of the last 10,000 years, according to different studies by scientists in France, Maine and their colleagues.

El Niņo and the U.S. economy

In the case of the 1997-98 El Niņo, severe storm damage was felt along the California coast, but the rest of the United States experienced a very mild winter. As a result, the U.S. economy experienced net savings of about $15 billion from averted fuel, heating and weather damage costs, plus 850 deaths avoided, according to Illinois researcher S.A. Chagnon.

The U.S. economy grew and carbon dioxide emissions decreased during the 1997-98 El Niņo. That led Nature on Aug. 5, 1999, to posit that the general link of economic growth to increased energy use - essentially of fossil fuels - might not be so strong. In turn, that would suggest that the Kyoto Protocol, with its demand for reductions in human-made greenhouse gas emissions primarily from burning fossil fuels, might not be so costly after all.

But the reduction in U.S. carbon emission despite economic growth likely resulted from lowered wintertime energy use and costs, partly owing to mild weather from El Niņo's warmth. In other words, blame global warming: The winter warming temporarily lowered the use of fossil fuels and resultant carbon emission, without stunting economic growth.

The 2002-2003 El Niņo should help increase understanding of this climate phenomenon. It also suggests preparation for bad weather that is associated with the complex and ill understood ENSO. However, it fails to support calls for expensive and ineffective cuts in carbon emission that would diminish the economic resources potentially available for dealing with recurring floods and drought that changing weather brings.

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