A team at the University of East Anglia has reconstructed the temperature peaks of every year in the last millennium, and these scientists are confident 1998 will be the warmest. Their research shows this year will have been hotter than 1106, the previous record summer in the northern hemisphere.
It is already certain to be the hottest year in the 140-year global temperature record that has been compiled from instrumental readings. In spite of Britain's own soggy summer, there have been record heatwaves and forest fires in many countries.
But scientists at the university's Climatic Research Unit (CRU) are convinced that, as 2000 approaches, 1998 will also prove to have been the hottest year of this millennium.
The scientists have put together the annual average summer temperatures of the last 1,000 years from "proxy indicators" - measurements of tree- ring growth and analysis of ice cores, which give information about the meteorological conditions deep in the past.
The record, published in the scientific journal The Holocene, shows that the 1990s were the hottest decade since before William the Conqueror landed.
The research will add further credence to global warming being caused by industrial gases, such as carbon dioxide from vehicle exhausts and power station emissions.
The research is published as ministers and officials from 180 countries begin a two-week conference in Buenos Aires to try to carry forward last year's Kyoto treaty aimed at countering climatic change.
The scientists at the CRU, led by Professor Phil Jones, are in a unique position to assess 1998 as the millennium's hottest year because they are also responsible for updating and maintaining the modern instrumental temperature record for the world, which goes back to 1855. Their data for this year already show that 1998 will beat the previous record - 1997 - by such a significant margin.
The five hottest years in the modern global temperature record are now all from this decade - in descending order: 1998, 1997, 1995, 1990 and 1991.
"The bottom line is that we believe the last three to four years have been the warmest of the millennium, and 1998 to have been the warmest of all," Professor Jones said.