Abstract:
The Earth's climate has changed throughout history. For example, fossils from the Cretaceous period (144 to 65 million years ago) show that Earth was much warmer than it is today. Fossilized plants and animals that normally live in warm environments have been found at much higher latitudes than they could survive at today. For instance, breadfruit trees, now found on tropical islands, grew as far north as Greenland. Earth has also experienced several major ice ages, at least four in the past 500,000 years. During these periods, Earth's temperature decreased, causing an expansion of ice sheets and glaciers.
A glacier is formed when the surplus snow that collects above the permanent snowline, where the losses to summer melting are less than the gains from winter accumulation slowly turn in to ice over a period of time and starts its down slope movement. The size of a glacier is determined primarily by climate. Changes in climate will cause its margins to expand or contract, because climate controls a glacier's mass balance. If the balance is positive (accumulation greater than ablation) it will expand and grow. If it is negative then the glacier will contract. If the accumulation equals ablation for a long time, the glacier remain in steady state. Glaciers are constantly responding to changes in their mass balance budget, adjusting to annual variations as well as to long-term trends (Glacial Geology - Ice Sheet and Landforms, 2009).
