ACT Reading Practice Test 44

NATURAL SCIENCE: El Niño: A Meteorological Enigma

Almost any mention of climate change brings thoughts of global warming, complete with mental images of rising seas and melting ice caps. While few reputable scientists contest the reality of global

Line 5 warming, most climatologists are also aware of other powerful meteorological phenomena that shape the weather on a daily, seasonal, or even multi-year basis. In fact, these “background oscillations,” or fluctuations, appear to cause major climate shifts every few

10 decades. Among the most influential are the North Pacific Oscillation (NPO), the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and the El Niño-Southern Oscillation (ENSO). Of these, probably the best-known is the El Niño-Southern

15 Oscillation, popularly called “El Niño.” The term El Niño was first reported in scientific circles in 1892. It originally referred to a local event: an annual, weak, warm ocean current that fishermen discovered along the central western coast

20 of South America. The current was most noticeable around Christmastime, which led to its name because El Niño is Spanish for “little boy” and is frequently used when referring to the Christ Child. (The reverse phenomenon, a cold ocean current, is known by a

25 corresponding term, La Niña, Spanish for “little girl.”) Along this area of South America, El Niños reduce the upwelling of cold, nutrient-rich water that sustains large fish populations. Predators such as larger fish and sea birds depend on these populations for survival, as

30 do local fisheries. As climatology developed as a discipline, scientists discovered that both trends in the current were part of a larger phenomenon affecting global climate patterns, the Southern Oscillation. The definition of

35 El Niño has therefore expanded and continues to change as climate researchers compile more data. Now scientists say that during El Niños, sea-surface temperatures over a large part of the central Pacific climb above normal and stay high for many months. This

40 creates a large pool of warm water that coincides with a change in wind patterns. The shift in wind patterns changes where evaporation takes place. Together, the warm water and shifting wind affect where storms form and where rainfall occurs on a global level.

45 Most of the time, strong El Niños bring wet winters to the Southwestern United States and milder winters to the Midwest. They tend to bring dry conditions to Indonesia and northern Australia. They generally occur every two to seven years. La Niñas usually,

50 but not always, follow El Niños. During La Niñas, water temperatures in the Central Pacific drop below normal, and weather patterns shift in the other direction. Together, the El Niño and La Niña cycles complete the El Niño-Southern Oscillation (ENSO).

55 ENSO weather oscillations are discrete from the NPO, NAO, and PDO weather patterns. This means one oscillation does not cause or usually influence the others. Sometimes, however, the various oscillations “beat” together at the same frequency, causing the

60 fluctuations to be synchronized. When this happens, scientists say the resulting weather can be intensified. Weather effects can be damaging. The warming patterns of El Niño are one of the leading causes of natural damage to coral reefs, while wider ENSO

65 fluctuations may cause flooding or drought to occur on land. In these cases, extreme shifts can cause economic pressure by disrupting entire fishing industries or damaging crops. Sometimes, pressure caused by intense weather

70 can have unexpected political effects. Some scientists argue that unusually cold weather brought by a strong El Niño phenomenon caused significant crop damage in 1788–89, which many say contributed to the French Revolution. Other climate researchers claim that strong

75 oscillation coupling, combined with strong El Niños in the late 1930s and early 1940s, led to a profound cold snap in Northern Europe in the middle of the Second World War. The scientists argue that this unexpected cold snap significantly contributed to the failure

80 of Germany to capture Moscow, which changed the course of World War II. ENSO phenomena, along with the other three oscillations, are separate from those attributed to global warming. The causes are completely independent.

85 However, because El Niño and global warming both can result in strong temperature variability, disruptive rain distribution, and extreme damage to a variety of ecosystems, any synchronicity will be closely observed by scientists seeking to document the total effects

90 of each.