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S P E C I A L S El Niño Returns
The Global Warming Debate

1997 hottest year on record

Satellite graphic
Satellite graphic illustrating the abnormal ocean surface temperature in the Pacific as of the end of September 1997. The dark red areas represent warmer water off the coast of Ecuador and Peru, while green and yellow represent cooler water temperatures in the surrounding areas.   
January 8, 1998
Web posted at: 2:00 p.m. EST (1900 GMT)

WASHINGTON (CNN) -- 1997 was the hottest year on record, and scientists predict the Earth's warming trend will continue, officials with the National Oceanic and Atmospheric Administration said on Thursday.

The combined ocean and land temperatures, gathered from weather stations all over the globe, averaged three-quarters of a degree Fahrenheit above normal, NOAA senior scientist Tom Karl said. A "normal" temperature is defined as 61.7 degrees Fahrenheit, the mean temperature from 1961 to 1990.

Since 1900, the Earth's average temperature has risen more than 1 degree Fahrenheit, with land temperatures rising 20 percent faster than ocean temperatures, Karl said.

Land temperatures rise faster because they respond faster to external forces, like greenhouse gasses, he added.

"We are beginning to understand..." the aspects surrounding El Nino -- Joe Friday
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"Warmest year on record..." -- Tom Karl
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Many scientists believe that carbon dioxide and other gases released into the atmosphere by industrial activities are increasing the Earth's temperature by trapping heat from the sun, somewhat like a greenhouse.

"Land temperatures (for 1997) did not break the previous record set in 1990, but 1997 was one of the five warmest years since 1880," said Karl. Including 1997, the top 10 warmest years have all occurred since 1981, with the five warmest years occurring since 1990.

"The increasing trends of temperatures we see we believe is at least partially attributed to human activities." he said.

Studies suggest a 5 to 10 percent chance that humans are not contributing to global warming, Karl said.

El Niño did contribute to some of the ocean warming, but "even without El Niño... 1997 would have been a very warm year," Karl said.

Interestingly, global warming is not occurring at a universal rate.

Eastern North America, parts of the Mediterranean, and parts of Asia, particularly China, typically have cooler temperatures than the rest of the globe.

Scientists say this is due in part to sulfuric emissions injected into the atmosphere. Sulfur particles, that can be emitted through volcanic eruptions and other natural events, tend to reflect radiation back into space. But since they only have a life span of seven days, the cooling is limited to the Earth's regions where the event took place.

The El Niño effect

El Niño
A 3-D diagram of the geographical effects of an El Niño event   

Scientists say the "jury is still out" on whether global warming is contributing to El Niño, the phenomenon that creates a warming of the Pacific Ocean waters off South America.

But, Karl said, "We don't know that this El Niño event is totally unrelated to the emission of greenhouse gasses."

An rise in sea levels in certain parts of the Pacific is one side effect of El Niño.

There has been a 6-inch rise in overall sea levels since 1900, and scientists predict an overall sea level rise of 1 to 3 feet in the coming century, said NOAA administrator Joe Friday.

Melting polar regions

While the overall Earth system is warming, perhaps currently the most visual side effect of the continued global warming is the melting of polar ice.

"We're seeing across the entire Arctic Circle melting of permafrost," Friday said.

Scientists say the melting could have a "significant impact" on Alaska, and other regions that are built along ice structures, because the melting continues to weaken the foundation.

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