Tomorrow's Forecast: Oceans and Weather

Whether you live on the gentle rolling plains of the Midwest or the glittering desert sands of the Southwest – no matter where in the world you are – your life is intimately tied to our planet's oceans. Even if you've never gone to a beach to watch a sunrise or sunset or to ride the waves, the oceans probably affected you as recently as this morning – when you may have checked the weather and decided what to wear.

The oceans influence the world's climate by storing vast amounts of solar energy and distributing that energy around the planet through currents and accompanying atmospheric winds. Dramatic weather events like hurricanes originate at sea, and the oceans also influence long-term conditions such as average daily temperature and rainfall. These factors in turn affect the variety and volume of crops that can be grown and the number of fish that can be caught. In fact, the oceans affect all life on our planet.

In the complex recipe of Earth's climate and weather, no ingredient is more important than the Sun. Without its intense energy, life on our planet would be impossible. At an average distance of 93 million miles (150 million kilometers), only 1/2 billionth of the Sun's energy reaches Earth. Yet even that fraction of the Sun's power is massive—totaling some 1.8 × 1014 kilowatts, or more than 300,000 times the electrical generating capacity of the United States!

Not all of that solar radiation reaches the surface of Earth. Some energy is scattered by the atmosphere on its way to the surface or is reflected back by the clouds, leaving about 45 percent to complete the journey. This solar radiation is absorbed (as heat) in differing amounts by the various surfaces on Earth. Land areas heat up quickly during the day and cool rapidly at night, radiating much of their energy back to space. Luckily, atmospheric gases such as carbon dioxide and water vapor retain certain types of radiation that warm the atmosphere. Scientists have termed this phenomenon the greenhouse effect.

As compared with the continents, the world's oceans absorb much more of the incoming solar radiation and reflect much less back to space. That is because water has a higher heat capacity (holds more heat per unit volume) than land or air. Not surprisingly, the oceans' higher heat capacity directly affects the climate of our planet. The insulating effect of water gives coastal areas a more moderate range of temperatures than inland areas have at the same latitude.

The energy from the Sun (in the form of heat) fuels the circulation of Earth's atmosphere. Regions near the equator receive more heat than those near the poles. Warmer, lighter air rises at the equator while cooler, denser air sinks at the poles. This sets up a pole-to-equator movement of air at the surface and an equator-to-pole movement of air aloft, although actual atmospheric circulation is somewhat more complex. Because of Earth's rotation, atmospheric winds appear to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Ocean Currents—Going with the Flow

The circulation of the world's oceans generally mirrors the movements of the atmosphere. Surface currents driven by atmospheric winds move warm equatorial waters to the poles and cold polar waters toward the equator—setting up nearly circular patterns of movement known as gyres. Before steam-powered ships were introduced in the nineteenth century, sailors used these winds and currents to cross vast stretches of ocean. Many of the routes they took, such as those between Europe and America, were physically longer than the trade routes used today. Rather than setting out directly west from Europe, sailors moved parallel to the west coasts of Europe and North Africa until they reached the "trade winds" that carried them westward across the Atlantic to the Caribbean.

Today scientists recognize that ocean currents are more than natural highways of commerce. These massive movements of ocean water play a pivotal role in determining the climate of Earth, although their behavior is not entirely understood. And, of the myriad currents flowing through the open ocean and along the edges of continents, the Gulf Stream may have the greatest influence on climate.

This swift-moving current transports more than 100 times the outflow of all the world's rivers as it moves northeastward from Cuba to Newfoundland. Caribbean heat continues eastward (in the form of the North Atlantic Drift), greatly moderating the coastal European climate. Much of Britain, the southern parts of which lie north of the U.S.–Canadian border, experiences winters as mild as those of northern Florida, Georgia, and South Carolina, which are fifteen to twenty degrees in latitude further south!

The counterpart to the Gulf Stream in the Pacific is the Kuroshio (or Japan) Current, which moves from the Philippines northward past Taiwan and Japan. Overall, the climatic effects of the Kuroshio Current are less extensive than those of the Gulf Stream. Towering mountain ranges along the west coast of North America confine the effects of the current's waters to relatively small areas. Other, similar currents affect climate on the rest of the planet. The relatively cold California, Peru, Benguela, and Canary Currents flow around the west coasts of the Americas, Africa, and Europe, creating cool, moist surface air with frequent fog and overcast skies.

An Ocean of Difference: El Niño—An Ocean Child

Not all ocean waters have a moderating effect on weather and climate. A massive ocean-atmosphere interaction in the tropical Pacific known as El Niño has brought about climatic devastation worldwide. The term El Niño (Spanish for "the Christ Child") was coined more than a century ago by Peruvian and Ecuadorian fishermen who noted that in some years a warm ocean current appeared during the Christmas season and lasted for several months.

The strongest El Niño event of this century occurred from 1982 to 1983 and has been blamed for $8 billion in damage worldwide. Climatic effects of this El Niño included drought and brush fires in Australia, Indonesia, southern India, and parts of Africa and Brazil. In contrast, heavy rains fell along the equator, in Southern California, and the southeastern United States, while winter temperatures soared far above normal in the interior of Canada.

While scientists do not entirely understand the causes of El Niño, they believe that it is linked to dramatic atmospheric changes that typically occur over the North Pacific every 2 to 7 years. In normal years, prevailing winds blowing from the east help to push Earth's warmest ocean water into the western Pacific. For reasons that aren't clear, occasionally the prevailing winds weaken and the warm water begins to move eastward across the Pacific toward South America—starting El Niño.

El Niño's effects extend far beyond the South American coast. Storm systems that would normally have been kept farther west by the prevailing winds move into the central equatorial Pacific, bringing heavy rain to typically dry islands. These heavy storm systems further disrupt the normal flow of the jet streams across the Northern Hemisphere. In any El Niño year the polar jet stream shifts northward over western North America, resulting in mild winters over western Canada and the north central United States. At the same time the subtropical jet stream is more vigorous than normal, bringing heavy rainfall to the southern United States.

Tomorrow's Forecast

Every day scientists gather vast amounts of data about the world's oceans from Earth-orbiting satellites, ocean-traversing research vessels, and drifting buoys. Advanced computer models process this raw data, helping scientists to forecast not only the probability of common weather systems but also the dramatic effects of El Niño. These efforts have been so successful that individuals, corporations, and governments alike have come to depend on weather and climate forecasts to make critical choices.

Whether it's a decision to plant more or less of a crop, to import or export a product, or to invest in a developing technology, the ocean is an important factor. Yet there is still much to be learned about the complex interactions between the ocean and atmosphere in determining our planet's weather. The ocean and atmosphere are so intertwined that it is often unclear which is driving the other at any given time. However, whatever the process, the ocean will always play an important role in tomorrow's weather.

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This article is reprinted from the September/October 1995 issue of Art to Zoo: Teaching with the Power of Objects, published by the Smithsonian Institution, (Retrieved August 29, 2006 http://www.paec.org/david/ttt/si/ocean.pdf)

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Copyright October 2006 — The Ohio State University. This material is based upon work supported by the National Science Foundation under Grant No. 0424671. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

This work is licensed under a Creative Commons License.