Pinatubo and El Nino fight tug of war.

January is a month made for breaking New Year's vows and for assessing how the climate behaved over the previous year. According to analyses presented last week by two research teams, Earth's average temperature in 1991 ranks as the second highest on record, continuing a pattern of global warming that emerged during the 1980s.

"Although it is still too early to link the recent concentration of warm years with the influence of increasing greenhouse gases, international scientific opinion strongly supports the reality of the greenhouse effect, and it is likely that this has played some role in contributing to the recent warmth," concludes a group of climate researchers from the United Kingdom Meteorological Office in Bracknell and the University of East Anglia in Norwich.

The U.K. group analyzed both land and sea-surface temperatures measured around the globe, while a separate team from NASA's Goddard Institute for Space Studies in New York City focused on measurements from land stations.

The British researchers' analysis shows 1991 finishing 0.05 [degrees] C cooler than 1990, which was the warmest year in their 140-year-long record. The NASA investigators found last year 0.08 [degrres] C below 1990, which holds top position in their 111-year-long record.

Balloon measurements taken in the lower atmosphere at 63 sites around the world also show 1991 as a warm year. In this 33-year-long record, 1991 qualifies as the fourth warmest, coming in close to 1988 and 1983, the second and third top years, says James K. Angell of the National Oceanic and Atmospheric Administration (NOAA) in Silver Spring, Md.

In all three data sets, 1991 started off very warm in comparison to other years, and then colled in the second half of the year, in part, perhaps, because of the eruption of Mt. Pinatubo in the Philippines last May. After the eruption, researchers predicted that sulfur gases from the volcano would block out sunlight, cooling the climate for a few years (SN:8/31/91, p.132). James Hansen of the Goddard Institute says the volcanic cooling should reach its maximum strength later this year and next year.

Global temperatures may not drop excessively in 1992, however, because an El Nino has been growing in the equatorial Pacific since last summer (SN: 12/14/91, p.389), and NOAA scientists formally announced its existence this week.

Caused by oscillations in the ocean and atmosphere, El Nino events push warm water from the West Pacific toward the East Pacific, raising temperatures across the ocean. In December, the patch of abnormally warm water had spread along the equator one-quarter of the way around the globe. The El Nino may intensify over the next few months, but should run its course by the end of the year, says Vernon E. Kousky of NOAA in Camp Springs, Md.