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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 12, NUMBER 4, APRIL 1999

JOURNAL ARTICLES...
SURFACE FREEZING

Item #d99apr9

“Simulated Climate Change Effects on Year-Round Water Temperatures in Temperate Zone Lakes,” H. G. Stefan, X. Fang, and M. Hondzo,Climatic Change 40, 547-576 (1998).

Computer simulations indicate that a doubling of CO₂ would delay ice formation up to 20 days and shorten the ice-cover period up to 58 days in temperate lakes and produce temperature modifications throughout the year, with water surface temperatures increasing 3 to 4° C and summer stratification becoming stronger.

Item #d99apr10

“The Natural Fluctuations of Firn Densification and Their Effect on the Geodetic Determination of Ice Sheet Mass Balance,” R. J. Arthern and D. J. Wingham,Climatic Change 40, 605-624 (1998).

A model of firn density was developed, checked against observational data from Antarctica and Greenland, and found to be accurate within 10%. The model was then used to determine the effects of natural climate variation on firn density. Temperature effects on firn density are transmitted by conduction through the upper 30 m of firn; accumulation effects immediately affect only the upper 10 m. In both cases, the effects on densification were so small that they would not unduly affect the use of the geodetic method of measuring the ice-sheet mass balance.

Item #d99apr11

“Model Computations of the Impact of Climatic Change on the Windthrow Risk of Trees,” H. Peltola, S. Kellomäki, and H. Väisänen,Climatic Change 40, 17-36 (1999).

Mean winds of 11 m/s are enough to uproot Scots pines when the soil is not frozen; freezing helps hold the roots in place. Monthly wind-speed statistics for Finland for 1961 to 1990 were used in conjunction with model-derived estimates of the effects of a 4° C increase in mean annual temperature to determine the effects of global warming on the windthrow loss of this species. Surface soil frost is expected to decrease from 4–5 to 2–3 months per year in southern Finland and from 5–6 to 4–5 in the north. Shortening of the freezing season could be even greater deeper in the soil. In the warmer climate, 85% of the damaging winds would occur during the unfrozen season, as compared with 55% at the present in southern Finland. In northern Finland, the number would be 50%, compared with 40% today.