Washington ? The Earth is running a slight fever from greenhouse gases, after enjoying relatively stable temperatures for 2,000 years.

The National Academy of Sciences, after reconstructing global average surface temperatures for the past two millennia, said Thursday the data were “additional supporting evidence … that human activities are responsible for much of the recent warming.”

Other new research showed that global warming produced about half of the extra hurricane-fueled warmth in the North Atlantic in 2005, and natural cycles were a minor factor, according to Kevin Trenberth and Dennis Shea, of the National Center for Atmospheric Research, a research lab sponsored by the National Science Foundation and universities.

The academy had been asked to report to Congress on how researchers drew conclusions about the Earth’s climate going back thousands of years, before data was available from modern scientific instruments.

Combining that information gave the panel “a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years,” the panel wrote.

The panel’s conclusions were meant to address a well-known graphic among climate researchers – a “hockey-stick” chart created in the late 1990s to show the Northern Hemisphere was the warmest it has been in 2,000 years.

It had compared the sharp curve of the hockey blade to the recent uptick in temperatures – a 1 degree rise in global average surface temperatures in the Northern Hemisphere during the 20th century – and the stick’s long shaft to centuries of previous climate stability.