The year 2007 has tied 1998 for the Earth’s second warmest this century, NASA scientists announced today.

Climatologists at the agency's Goddard Institute for Space Sciences (GISS) in New York used temperature data from weather stations on land, satellite measurements of sea ice temperature since 1982 and data from ships for earlier years to construct a record of global average temperatures going back for over a century.

The GISS analysis has 1934, 1998 and 2005 tied as the warmest years in the United States (with 2005 being the warmest globally).

The eight warmest years globally in the past century have all occurred since 1998, and the 14 warmest years have all occurred since 1990.

The greatest observed warming in 2007 occurred in the Arctic, which experienced a record sea ice melt this summer, opening up the fabled Northwest Passage for the first time.

"As we predicted last year, 2007 was warmer than 2006, continuing the strong warming trend of the past 30 years that has been confidently attributed to the effect of increasing human-made greenhouse gases," said NASA GISS Director James E. Hansen.

A minor flaw in the GISS record discovered last year did not affect this analysis, the scientists noted.

Hansen says that warming can be expected to continue, with another record warm year coming soon, though it is unlikely to be 2008.

"Barring a large volcanic eruption, a record global temperature clearly exceeding that of 2005 can be expected within the next few years, at the time of the next El Nino , because of the background warming trend attributable to continuing increases of greenhouse gases," Hansen said.

El Nino tends to have a warming effect on temperatures in many areas, while the volcanic ash that an eruption spews into the air has a cooling effect.

While most scientists agree the planet is warming, the trend does not proceed constantly upward year-by-year. Other factors cause hikes and dips in the generally trajectory of the global temperature chart, which has been mostly trending upward since the beginning of the 20th century.