Northern Hemisphere’s Warmest Years Since 1400 Were ‘97, ’95 and ’90

The years 1997, 1995 and 1990 were the warmest in the Northern Hemisphere since the days of Christopher Columbus, according to researchers from the University of Massachusetts at Amherst. And the researchers say that they found evidence that rising levels of greenhouse gases are probably responsible.

Geoscientist Michael Mann and his colleagues reconstructed annual average temperatures back to the year 1400 and found no year warmer than those three, they report in today’s Nature. Either 1997 or 1995 could be considered the warmest, depending on whether one considers temperatures over land or at the ocean surface or both, Mann said. When land and ocean temperatures are combined, 1997 and 1995 ran about nine-tenths of a degree Fahrenheit above the average for the 20th century, he said.

Compiled by Times medical writer Thomas H. Maugh II