'88 set warm record: '89 looks cooler.

'88 Set Warm Record; '89 Looks Cooler

Global temperature measurements show 1988 as the warmest year in a century of recorded weather information, British climatologists reported last week. Last year joins a string of recent years that have topped the temperature charts and thereby transported the term "greenhouse effect" from scientific journals into the public lexicon. However, experts do not expect 1989 to follow suit, because a climate phenomenon in the Pacific is now causing ocean temperatures to drop and should make this year significantly colder than 1988.

Researchers at the United Kingdom Meteorological Office and the Climatic Research Unit of the University of East Anglia in Norwich, England, found that the global average temperature for 1988 exceeded by 0.34[deg.]C the average for the period 1950-1979. The year 1987, the second highest mark, was only slightly cooler at 0.33[deg.]C above the 30-year average, says climatologist Phil D. Jones from East Anglia. In total, the 1980s claim six of the warmest years in the last century (SN: 4/30/88, p.282).

The researchers based their analysis on a global average of land and sea surface temperatures measured at nearly 1,000 stations.

Reflecting the caution of most climate experts, Jones and his colleagues hesitate to blame the recent warm years on the rising atmospheric concentrations of many "greenhouse" gases such as carbon dioxide, methane and chlorofluorocarbons. "It's still a bit ambiguous. We can't associate this warming with the greenhouse effect," Jones says, while adding: "I think it's the most likely cause."

Researchers can speak more firmly about the effect of the climate phenomenon known as the El Nino-Southern Oscillation (ENSO). During an ENSO, a large patch of warm water develops in the central equatorial Pacific at about the same time the atmospheric pressure drops over the eastern part of the ocean relative to the west. Lasting about a year to 18 months, ENSOs rearrange traditional patterns of precipitation, bringing fierce rains to coastal Peru and drying out India and Australia. The individual events recur roughly three to seven years apart, and scientists have yet to determine what causes the phenomenon.

The year 1983 saw the strongest ENSO in a century. The next ENSO developed in early 1987 and carried through into early 1988. Jones says it is clear these events helped raise global temperatures during 1983, 1987 and part of 1988. But even with the ENSO effect removed, these years remain warmer than the 30-year mean, he says. It is this background warming that has scientists concerned.

Jones and most other climate experts expect global temperatures to drop markedly in 1989 due to a climate phenomenon that resembles the reverse of an ENSO. Scientists have yet to agree on what to call this interaction between the ocean and atmosphere. Some have named it the "cold phase" based on ocean temperature. Others call it the anti-El Nino. Still others have dubbed it La Nina, which is Spanish for "the girl," in an attempt to give it equal footing with El Nino ("the boy" or "Christ child," a reference to its winter timing). The confusion over names reflects the fact that scientists have only recently recognized the importance of this phenomenon.

Chester Ropelewski and Michael Halpert of the Climate Analysis Center of the National Oceanic and Atmospheric Administration in Camp Springs, Md., have completed a statistical examination of precipitation records around the globe, and they find several recurring patterns associated with La Nina. The researchers focused on 19 areas of the globe that clearly experience some sort of effect during ENSOs and found that 15 of the regions also show characteristic precipitation change during La Ninas. These results will appear in an upcoming issue of the JOURNAL OF CLIMATE.

Ropelewski and Halpert found that during most La Ninas, Indian and Australian summer monsoons strengthen, as do the rainy seasons in northeastern South America and southeastern Africa. Some areas, like the Gulf of Mexico, tend to dry out. In general, ENSOs and La Ninas affect these regions in opposite manners.

At last week's meeting of the American Meteorological Society in Anaheim, Calif., Ropelewski reported the current La Nina seems to be progressing true to form. By mid-1988, water temperatures in the central Pacific had plummeted to abnormally cold levels, signaling a climate swing directly from an El Nino into a La Nina. Such a pattern does not always occur. For instance, two ENSOs developed between 1976 and 1984, but no La Nina split the two warm phases.

As expected during a La Nina, strong monsoons pounded India and Bangladesh last summer. Then, in December, heavy rains visited Australia, repeating the pattern of most La Ninas, Ropelewski says. Even weather in Alaska seems in character. The bitter cold felt in this region during recent weeks follows the statistical La Nina temperature pattern for the area.

Jones says the La Nina has already started to cool ocean temperatures, but land temperatures have not yet followed. He says the average global temperature for 1989 should drop from this year's high, although he still expects it to exceed the 30-year mean. Climatologists are laboring to determine if this background warming is indeed caused by the greenhouse effect, or by some unknown natural climate shift. The natural variation could be analogous to something like a century-long version of the ENSO.