The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Climate in Earth History: Studies in Geophysics
FIGURE 14.1 Approximate limits of year-round Arctic Ocean ice cover.
weather modification is based on satellite data that showed that the ice cover was 12 percent greater in 1971 than in 1970. This produced a surface-heat-exchange deficit for the Arctic that was correlated with anomalous weather patterns in lower latitudes during 1972 and 1973 (Kukla and Kukla, 1974).
Some of the effects are more complex. Other data show that the Arctic region (Greenland, in this example) and northern Europe are out of phase in terms of severity of winter temperatures. This has been described as the “seesaw effect.” Colder Arctic (Greenland) winters commonly correlate with mild northern European winters and vice versa (van Loon and Rogers, 1978). The temperature anomaly is correlated with anomalous weather effects over wide areas including the southern Mediterranean, the Middle East, Central America, western North America, and Alaska. Explanations for this temperature anomaly are related to pressure anomalies as well as to general atmospheric circulation.
An interesting model of world climate and its relationship to astronomical theories of ice ages includes cooling and heating parameters; heat transport; seasonal variation in Arctic ice cover; and a variety of Earth obliquity, eccentricity, and precession factors (Pollard, 1978). A number of conclusions derived from the still imperfect model include the observations that variation in extent of ice cover would have a profound effect on world climate. Nonetheless, the totality of cryospheric processes including feedback mechanisms for the Arctic Ocean and the relationship to world climate is only partially understood (Polar Group, 1980).
However, both observations and models furnish suggestive data regarding the effect of the Arctic ice cover on world climates.
WORLD CLIMATE AND AN ICE-FREE ARCTIC OCEAN
Polar ice covers are basic to the generation of atmospheric circulation. Removal of the ice covers would reduce the thermal gradient and change circulation. The extent of the change that would be produced has not been quantitatively described, in fact “… a realistic model of the entire planetary circulation under the assumption of an ice-free Arctic Ocean is not yet available…” (Fletcher and Kelley, 1978, p. 103). Nonetheless, there are data suggesting how the absence of an Arctic ice cover would greatly modify world climates. For example, during the summer, an ice-free Arctic Ocean would absorb 90 percent of solar radiation reaching its surface in contrast to the present figure of 30 to 40 percent (Fletcher and Kelley, 1978). Such a change would affect the Earth’s heat budget.
There is disagreement on the actual heat balance of an ice-free Arctic. One argument is that under ice-free conditions the Arctic Ocean would gain approximately 40 kcal/cm2 in summer but lose a similar amount in the winter for a balance (Fletcher and Kelley, 1978). Others argue that there would be a smaller heat loss in the winter, resulting in a yearly net increase in ocean temperatures (Donn and Shaw, 1966).
Year-round open water in the Arctic would be a source for increased atmospheric moisture. The surface temperature of an ice-free Arctic would be critical in determining how much. At 0–5°C surface temperature, the Arctic would give only a fifth to a sixth as much moisture to the atmosphere as water at 25–30°C, under similar wind conditions (Lamb, 1974). Nonetheless, an ice-free Arctic Ocean would contribute to warmer atmospheric conditions that could produce an increase in precipitation for Canada, India, the Middle East, and China and a sharp decrease in precipitation for most of the United States, Eurasia, and much of northern Africa (Wigley et al., 1980).
Such conclusions would be more impressive if framed in quantitative terms, but in the absence of complete modeling of these conditions, it may be safe to conclude that change in precipitation patterns in addition to other changes in atmospheric gradients produced by an ice-free Arctic would be a factor in amelioration of northern hemisphere climate.
DEVELOPMENT OF THE ARCTIC OCEAN
Having examined questions related to the effect of an ice-covered. and ice-free Arctic Ocean on world climate, it is necessary to discuss the geologic development of the Arctic. What is known about the absence or presence of ice cover during the development of the Arctic Ocean? The size and position of the Arctic Ocean have changed as crustal plates have adjusted, By the Cretaceous, the present position of the Arctic Ocean was approached (Firstbrook et al., 1972; Smith and Briden, 1977), but the ocean was only one half as large as it is at present. As the North Atlantic opened, spreading along the Nansen Ridge doubled the size of the Cretaceous Arctic Ocean (Figure 14.2) to its present dimensions (Clark, 1977a, 1977b, 1981); in this setting, sea ice was to form, but not quickly.