Bullet iv: Ice and Sea Levels

Bullet iv: "A clear warming trend is evidenced by ice sheet and sea level changes"
Hierarchy: Part II:1:A:iv

Back to Intro - Back to Outline - Back to Bullet iii - Forward to Bullet v

Introduction
It would be logical to assume that a warming world should be losing ice cover. But the relationship between warming and polar ice sheets is not simple. Warming does not simply melt ice; it also changes weather patterns that affect the accumulation of ice. Warmer polar air can carry more moisture and thus increase the amount of precipitation over ice fields, effectively increasing the amount of ice. If precipitation outweighs melting and evaporation [positive "mass balance"], then warming could actually increase the ice in polar fields. Also, the equilibrium-line altitude [ELA]--the altitude above which there is net ice accumulation--increases with increased temperature but decreases with increased snowfall, so it is not necessarily clear from ELA trends whether warming has occurred.

But it is still true that polar ice presents a potentially powerful testament to climate trends. The expected contribution to the mass balance from increased precipitation is small compared to increased melting. And also the distribution of ice changes in predictable ways according to temperature. Below the ELA, the rate of melting should undeniably increase with increasing temperatures. A signature of warming would then be ice thickening in the interior and thinning or retreating around the periphery. The flow of ice into the ocean is also expected to accelerate with rising temperatures; scientists have recently shown that the melting of sea ice abutting the mouths of glaciers triggers a massive acceleration of the glacier. And further evidence has been found that surface meltwater can percolate to the bottoms of glaciers and lubricate the ice-rock boundary, catalyzing faster ice flow. If sea levels are rising then the net amount of water tied up in ice worldwide must be decreasing, which would be an undeniable sign that temperatures are increasing despite increases in snowfall.

Glaciers and polar ice fields are very different beasts. Glaciers represent a much higher diversity of the planet's climates and thus tell us more about global temperature trends. Glaciers also are more a part of their surrounding climate than ice sheets in Greenland and Antarctica, which are so large that they create their own regional climates. So glaciers can respond faster to climatic variations. An analysis of ice cover then wouldn't be complete without a discussion of the trends in the distribution of continental glaciers.

Changes in the distribution of polar ice, glacial ice and sea levels are all important in an analysis of what ice can tell us about temperature trends. Each topic contains enough data to evaluate independently, so we will follow the structure below. Click on the links to see an analysis of the research for each topic.

Bullet Structure:

A clear warming trend is evidenced by ice sheet and sea level changes

a. The Greenland ice sheets show warming

b. The Antarctic ice sheets show warming

c. Global continental glaciers show warming

d. Sea levels show warming

e. Permafrost and river and lake ice show warming

Conclusion
No conclusion at this time.

Bullet Value: INCOMPLETE