The year 2002 is the second warmest year in recorded history, according to NASA scientists who monitor global air temperatures.

A record-breaking string of warmth in recent years — with 2001 now going down as the third warmest year on record and 1998 still holding the record — has scientists and climate experts concerned that greenhouse gases are warming the planet more quickly than previously expected.

“Studying these annual temperature data, one gets the unmistakable feeling that temperature is rising and that the rise is gaining momentum,” said Lester R. Brown, an economist and president of the Earth Policy Institute in Washington.

The Earth’s temperature during the 2002 meteorological year was 58.35 degrees Fahrenheit, more than one degree warmer than the long-term average of 57.2 degrees, said James E. Hansen, a climate scientist at the National Aeronautics and Space Administration’s Goddard Institute for Space Studies who analyzes surface temperatures collected from several thousand weather stations around the world.

The meteorological year runs from December to November. During that period, 2001 temperatures were 58.12. The record year remains 1998, when global temperature rose to 58.41 degrees Fahrenheit. The numbers are the highest since temperature records were first compiled in the late 1800s.

The string of warmer years provides strong evidence that humans are in large part to blame for changing the climate, said Peter Frumhoff, an ecologist and senior scientist with the Union of Concerned Scientists in Cambridge, Mass.

“It’s important we pay attention to this drumbeat of evidence as the signal of human impact starts to emerge from the noise of natural climate patterns,” he said.

The warm temperatures of 2001 and 2002 are especially significant when they are considered in the light of El Niño weather patterns that alter global climate, Hansen said.

Some of the heat of 1998 can be attributed to a large El Niño event that year, which warmed the waters of the Pacific Ocean. But 2001 saw a La Niña event, which kept temperatures that year from soaring even higher. There is a weak El Niño developing now, but it is not generating nearly as much heat as the big El Niño of 1998.

Most of the warmth of 2002 was seen in Alaska, Siberia and the Arctic, two usually frozen areas that have experienced a massive loss of ice and thawing of permafrost.