[Regia-NA] New data on Medieval warm period

[Sharon Gordon]

Northern Hemisphere Climate Warmest in 2,000 Years

A new reconstruction of past temperatures at the Earth's surface suggests
that late 20th century temperatures in the Northern Hemisphere were higher
than at any time in the past 2,000 years. A lack of suitable data for the
Southern Hemisphere limited the conclusions that the researchers could make
about temperatures south of the Equator or for the globe as a whole.

Michael Mann of the University of Virginia and Philip Jones of the
University of East Anglia (UK) used surrogate temperature data inferred
from ice cores, lake sediments, tree rings, and fossilized shells for their
reconstruction. Data for the Northern Hemisphere covered eight distinct
regions, while data from the Southern Hemisphere covered five. Mann and
Jones rigorously standardized and compared the data with instrumental
records for the same region during the past century.

In general, Northern Hemisphere temperatures remained well below the 1961-
1990 average throughout the past 2,000 years. The reconstruction does show
a "Medieval warm period" in the Northern Hemisphere from about AD 800-
1400. "This warmth is, however, dwarfed by late 20th century warmth which
is observed to be unprecedented at least as far back as AD 200," the
authors state.

The research is reported in the 1 August 2003 issue of Geophysical Research
Letters (vol. 30, no. 15, pp. 1820-1823).

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