Researchers at the University of Massachusetts say the 1990s were the warmest decade of the millennium, and 1998 was the warmest year of the decade.

The study appears to add weight to the theory that the global temperature is rising as a result of human industrial activity, especially in the 20th century.

"Temperatures in the latter half of the 20th Century were unprecedented," one researcher said on Wednesday.

The report shows that temperatures dropped an average of 0.02 degrees Celsius for 900 years -- until the 20th century.

To determine the temperatures in the years before records were kept, the researchers used "proxy indicators" like tree rings and ice cores from around the world.

The scientists say that the data get sketchy the further back they looked, but it is still clear that dramatic warming has taken place in the last 100 years. That warming could spell trouble for the human race.

"If temperatures change slowly, society and the environment have time to adjust," said Michael Mann, of the University of Massachusetts. "The slow, moderate, long-term cooling trend that we found makes the abrupt warming of the late 20th century even more dramatic."

"The cooling trend of over 900 years was dramatically reversed in less than a century."

In January, the U.S. Government said data showed the 1990s to be the warmest decade of the 20th century.

Rising global temperatures could potentially spell disaster for humanity by melting polar ice caps, raising sea levels, and causing severe droughts, hurricanes, and tornadoes.