Science / Medicine : Volcano Slows Global Warming

The world’s average temperature was well above normal last year, but the eruption of Mt. Pinatubo may have kept 1991 from being the hottest year on record, climate researchers said last week. Climatologist James Hansen of the Goddard Institute for Space Studies said 1991 “appears to be the second-warmest year in our record,” falling slightly short of the high set in 1990.

Despite the slight decline between 1990 and 1991, the rate of warming of the globe over the last 25 years has been greater than at any time on record, Hansen said. The apparent 1991 cooling may have resulted from the eruption of Pinatubo in the Philippines. The volcano blasted tons of ash into the air, and the dust veil blocked some sunlight.

Monthly temperature readings indicate a cooling trend in the last five months of 1991, “consistent with the expectation . . . that stratospheric aerosols introduced by the Mt. Pinatubo volcano will substantially cool the Earth’s surface,” Hansen said. Helene Wilson of Columbia University, who works with Hansen, said that 1991 averaged 0.7 of a degree Fahrenheit warmer than the 30-year average. By comparison, 1990 had been 0.85 of a degree above normal.