Temperature data collected from more than 2,000 locations around the world shows that 1990 was the warmest year since comparable record-keeping began in the middle of the 19th Century, researchers in the United States and Great Britain reported Wednesday.
The finding, based on separate analyses by scientists at the University of East Anglia and by the National Aeronautics and Space Administration’s Goddard Institute for Space Studies in New York, is considered significant because it extends a trend that began in the 1980s. Six of the seven warmest years in more than a century were recorded during the decade.
Philip Jones, a senior researcher at the University of East Anglia, and James Hansen, an investigator at the Goddard Center, said in separate interviews that they consider the finding important because 1990 was a year in which there was no El Nino effect.
El Nino conditions arise from the episodic warming of the tropical Pacific off Peru and lead to surges of extreme drought and heat in the Northern and Southern hemispheres. They have been blamed for global temperature increases, particularly in 1988 and 1989.
The Goddard analysis of 1990 temperature records shows that the average surface temperature of the planet was 0.2 degree Fahrenheit warmer than during the previous year.
The average for the eastern United States and a huge region of Eurasia was more than 2 degrees above the average temperature recorded between 1951 and 1980, Hansen noted. “The only large region with temperature substantially below normal for the year was Greenland and the neighboring Canadian archipelago,” he said.
Scientists and environmentalists concerned about an acceleration of the planetary greenhouse effect point to higher temperatures in the 1980s as confirmation that pollution of the atmosphere already is causing global warming.
The new studies, Hansen said, constitute more bits of evidence to refute skeptics’ contentions that the warming trend observed in recent years is within the range of cyclical climate variation.
In addition to surface temperatures gathered from land stations and ships traveling the oceans of the Northern Hemisphere, Jones said, preliminary evidence shows that temperatures in the lower atmosphere were warmer in 1990 than in any year since record-keeping began in 1958.
Besides the global temperature analysis, two related studies were released by the World Resources Institute in Washington. One, by Richard Heim of the National Oceanic and Atmospheric Administration’s Global Climate Laboratory, concluded that 1990 was the seventh warmest year on record across the contiguous United States.