>>on the global warming and winters in Breughel's times<<
from Science 15th june - letter to editors - bold italics DJ
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The Scope of medieval Warming
Hemispheric mean temperatures that have been reconstructed with a wide range of climate proxies indicate that temperatures were warmer in Medieval times than during the subsequent "Little Ice Age". (~1550 to 1850) (I). However, all studies of large-scale climate variations reveal some regions that do not follow the global or hemispheric trend [for example, (2)], so selecting a few data points, as W. S. Broecker does in his Perspective (Science's Compass, 23 Feb., p. 1497), adds little to resolving the title question he poses: "Was the Medieval Warm Period global?"
Furthermore, Broecker's statement that only borehole temperatures and snowlines can reconstruct temperatures to within 0.5°C is not supported in the literature. Reconstructing global temperature requires a geographically extensive network of data. Studies that have analyzed data from a wider range of instruments than Broecker mentions (1, 3) conclude that 20th century warming is unprecedented, in both rate and magnitude, compared with warming during the past 1000 years.
Medieval climate was clearly unusual in some areas (4), and further regional studies are needed. These might help determine if Broecker's hypothesis of a change in thermohaline circulation holds water.
RAYMOND S. BRADLEY 1, KEITH R. BRIFFA 2, THOMAS J. CROWLEY 3, MALCOLM K. HUGHES 4,
PHILIP D. JONES 2, MICHAEL E. MANN 5
1.Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA.
2.Climatic Research Unit, University of East Anglia, Norwich NR4 7TJ, UK.
3.Department of Oceanography, Texas A&M University, College Station, TX 77843, USA.
4.Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA.
5.Department of Environmental Sciences, Uni4ersity of Virginia, Charlottesville, VA 22903, USA
To whom correspondence should be addressed. E-mail: rbradley@geo.umass.edu
References and Notes
1.P. D. Jones et aL, Holocene 8, 455 (1998); M. E. Mann, R. S. Bradley, M. K. Hughes, Geophya Res. Lett. 26,759 (1999); T. J. Crowley, T. S. Lowery, Ambio 29, 51 (2000).
2.P. D. Jones et al., Rev. Geophys. 37, 173 (1999).
3.M. K. Hughes, H. F. Diaz; Clim. Change 26, 109 (1996); K. R. Briffa et aL, J. Geophys. Res. 106D, 2929 (2001 ).
4.S. Stine, in Water, Environment and Society in Times of Climatic Change, A. S. Issar, N. Brown, Eds. (Kluwer, Dordrecht, Netherlands, 1998), pp. 43-67; M. K. Hughes, G. Funkhauser, in The Impacts of Climate Variability on Forests, M. Beniston, J. L. Innes, Eds. (Springer-Verlag, Berlin, 1998), pp. 99-107; C. Pfister et al., Holocene 8, S35 (1998); V. C. LaMarche, Science 183, 1043 (1974); D. Dahl-Jenssen et al, Science 282, 268 (1998).
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