EL NIÑO AND CLIMATE CHANGE: Record Temperature and Precipitation

Vice President Gore and NOAA scientists announced today that The 1997/98 El Niño, one of the most significant climatic events of the century, produced extreme weather worldwide. El Niños have become more frequent and progressively warmer over the past century, and new data and analysis suggest that global warming is exacerbating the effects of El Niño. Global temperatures for January-May 1998 substantially exceed previous records.

During this latest El Niño, temperature and precipitation records were broken across the United States. Many areas suffered heavy flooding, and a series of severe tornadoes has killed 122 people so far this year, already matching the annual record set in 1984. Elsewhere around the world, El Niño contributed to major droughts and wildfire in Mexico, Indonesia and Brazil; devastating floods in South America; and massive coral bleaching from Panama to Africa to Australia's Great Barrier Reef.

Globally, 1997 was the warmest year on record. Average temperatures for January-May 1998 have since set new all-time highs. Combined land and ocean temperatures for the five-month period exceed the previous record by 0.25 C (0.45 F).

Analysis of data from the ten strongest El Niños of the past century shows that they are occurring more frequently, and that they are becoming progressively warmer. These higher temperatures tend to produce more extreme weather events. Although El Niños occur cyclically, independent of any long-term warming trend, there is observational evidence to suggest that rising global temperatures may be linked to stronger, more frequent El Niños.

THE EL NIÑO PHENOMENON

El Niño, meaning "Little Boy" or "Christ Child" in Spanish, was the name given by fishermen to unusually warm water off the West Coast of South America. El Niños occur every few years and disrupt the ocean-atmosphere system in the tropical Pacific, which subsequently affects weather around the globe. Its far-reaching consequences include increased rainfall across the southern US and Peru, which has caused destructive flooding, and drought in the west Pacific, sometimes associated with devastating fires. During El Niño, the trade winds which normally blow west towards Indonesia, relax in the central and western Pacific, allowing normally cool, nutrient-rich waters off of South America to warm significantly, leading to a decline in these fisheries. As the Pacific's warmest water spreads eastward, the hot humid air which fuels thunderstorms moves with it. El Niño changes the position of the jet stream, winds which affect the weather not only in North and South America, but as far away as Africa and Antarctica.

THE 1997/98 EL NIÑO

The 1997-98 El Niño was first noted by numerical models and scientists at NOAA's Climate Prediction Center in early spring 1997 when sea surface temperatures (SST) in the equatorial Pacific ocean began to increase. By March 1997, the SSTs were approximately 1 C (1.8 F) above normal in the extreme eastern equatorial Pacific and the vicinity of the international dateline. By May 1997, the evolution of the atmospheric and oceanic conditions in the tropical Pacific were consistent with the beginning stages of warm episode, or El Niño, conditions. Along with the increased SSTs, tropical convection began to gradually shift eastward toward the date line. Numerical models indicated that a continued warming trend in the tropical Pacific would persist through the end of the year, and that the warm episode conditions would intensify during the summer. In May 1997, SSTs greater than 29 C (84 F) were observed from Indonesia to 160 W. Equatorial SST anomalies (departures from normal) exceeded +1 C from 175 W eastward to the South American Coast, with values greater than +4 C (7.2 F) observed in the extreme eastern Pacific. These strong conditions have persisted in the tropical Pacific Ocean since June 1997. As of May 1998, strong El Niño conditions continued as SSTs remained above 28 C throughout most of the region. The latest NOAA forecasts indicate a return to near normal conditions in the tropical Pacific during the next 3-6 months. Thereafter, the NCEP coupled model indicates that near normal conditions will persist through the end of 1998.

RISING GLOBAL TEMPERATURES

The most recent near-surface land and sea-surface ocean temperatures, based on weather stations, ocean ships and buoys, and satellites indicate that global temperatures for both land and ocean during 1998 (through May) far exceed all previous record high temperatures (FIGURE 1). Land temperatures are 0.32 C (0.58 F) warmer than any previous January-through-May period. Ocean temperatures are 0.20 C (0.36 F) warmer than any previous January-through-May period. Combined land and ocean temperatures exceed the old record by 0.25 C (0.45 F).

The warmth has clearly been reflected in the US. as temperatures have averaged 4 to 6 deg F above normal throughout the Great Lakes States and the Northeast. A number of new one-day record high temperatures were set during March of this year. They include: 92 F in Connecticut, 95 F in Maryland, 92 F in Massachusetts, 88 F in Vermont, 89 F in Maine, 92 F in New Jersey, and 89 F in New Hampshire.

The record warmth is continuing through May as initial data reports show near-surface land temperatures during May exceeding the previous record set in 1994 by 0.15 C (0.27 F). Ocean temperatures also continue to remain at record high levels in May, exceeding the previous record, set just last year, by 0.15 C (0.27 F). These record high ocean temperatures are persisting despite some cooling of ocean temperatures in the Equatorial Pacific related to the beginning of the demise of the recent El Niño event.

During the past few decades, global temperatures have persistently broken previous record highs every few years, but never to the extent observed in 1998. Each month this year has set a new all-time record high global temperature (FIGURE 2). This is unprecedented and is not likely to occur in a stationary climate. New analyses of tree-rings, historical records, and other proxy measurements indicate that these temperatures are warmer than the planet has experienced for at least the last 600 years.

EL NIÑO AND GLOBAL WARMING

Examination of data from the ten strongest El Niño events of the Century reveals two general trends: increasing frequency of El Niño events in the past few decades, compared to what was observed earlier this Century; and rising global temperatures during these events (FIGURE 3). It can not be determined from current evidence whether El Niños are becoming more frequent or more intense as a direct result of global warming. It appears evident, however, that the effects of El Niño could be compounded by rising global temperatures. In other words, the extreme weather and climate conditions related to naturally occurring El Niño events could be exacerbated by an ongoing global warming trend. The additional heat near the Earth's surface powers the energy required to evaporate enormous amounts of water. This affects the entire atmospheric water and energy balance.

El Niño events also strongly impact regional precipitation patterns. In the United States, for example, wet conditions ordinarily occur with El Niño events in the west, south, and southeast. This year, however, conditions have been wetter than average throughout virtually the entire country. This continues the Century-long trend toward wetter conditions in the USA, and more extreme rainfall and snowfall events.

Based on records dating back to 1895, many states have broken all-time records for mean temperatures and total precipitation during the period January-May 1998 (Figure Map). During the first five months of 1998, records for total precipitation were broken in California, Maryland, North Carolina, South Carolina and Virginia. For the same time period, Idaho had its second wettest year to date, Rhode Island its third wettest, Nevada its fourth wettest, and Massachusetts, Oregon, and Pennsylvania their fifth wettest year to date. Outside of California and Arizona
every state has had above average temperatures with 24 states experiencing much above normal temperatures (in the upper ten percentile). Thirteen states have had their warmest January - May period on record. Seventeen states had much above normal precipitation, nine states had both much above normal precipitation and temperature, and Maryland had both the wettest and warmest period on record to date.

While some regions experience heavy precipitation during El Niño, in others, increased global temperatures lead to conditions that are drier than normal. For example, during the past year, Indonesia and Central America have suffered droughts, which have contributed to catastrophic wildfires.

APPENDIX: JANUARY-MAY (YEAR-TO-DATE) TEMPERATURE AND PRECIPITATION
RECORDS IN THE CONTIGUOUS UNITED STATES

Many temperature and precipitation records were broken in the United States during the January through May period, with several regions and 17 states setting records for precipitation and temperature for this period. The Northeast region and 13 states had the warmest January through May period on record, while the East North Central and Central regions and the states of Illinois, Indiana, Maine and Minnesota had the second warmest January through May periods on record.
During the same period, the Southwest and West regions, and California, Maryland, North Carolina, South Carolina and Virginia broke records for precipitation dating back to 1985. Idaho also had the second wettest five-month period on record.

(Temperatures in degrees F, Precipitation in inches)

January-May 1998 was the wettest on record (back to 1895) for 2 regions and 5 states:

Region  1998
Value 1998 Percent
of Normal 1961-90
Normal Second Wettest
Value & Year  Southeast 27.72" 134% 20.76" 27.31 in 1979 West 19.66" 218% 9.03" 19.04" in 1995  State 1998
Value 1998 Percent
of Normal 1961-90
Normal Second Wettest
Value & Year California 28.04" 228% 12.31" 27.49" in 1909 Maryland 24.55" 141% 17.39" 24.45" in 1924 North Carolina 29.20" 145% 20.08" 26.31" in 1979 South Carolina 29.98" 149% 20.17" 28.64" in 1929 Virginia 27.88" 162% 17.26" 23.30" in 1984

| Publication of the NOAA Home Page Design and Construction Company.