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Ablation is a term reserved for glacier reduction in size. Glaciers have year long periods of growth and melt back depending on summer or winter weather patterns, storms, clarity of the air and CO2 parts per million. Ablation refers to the phenomenon of shrinkage that is not later fully replaced by more snow and ice at the end of a four season year. When one says that a glacier's ablation was 4%, one means that a glacier completed its yearly cycle at 96% of the previous year's cycle, in size. . Ablation as a term is under attack by some glaciologists who contend that ablation does not describe the volume of glacier loss, which they contend is more important than the area lost. Many glaciers are being cited by scientists who describe example glaciers as having lost 50 percent of their volume while only shrinking in size by 15 percent ablation measured in terms of square area. They contend that melt water, below the visible surface of glaciers erode and carry away far more of the under story of glaciers than is known or understood by visual or infra red satellite surveys. These scientists contend that glaciers tend to melt from the bottom up, which has the effect of hiding the amount a glacier has melted until most of it has disappeared. (See: Glacier National Park). . Some contend that the effects of under story melt will show up most drastically, during the last few years of a glaciers death cycle. Some climatologists who factor in the accelerated volume being lost, but still not visible, say that the North pole will be down to 10 percent of its year 2000 volume by 2050 if the green house gas, CO2 is not drastically reduced in the atmosphere from its current volume of 648 PPM and gaining, within 10 years. While the temperature rise of current carbon dioxide levels is 3% higher than "normal," that differential is at the root of enormous erosion of the worlds remaining glaciers. . Glacier ablation is expected to noticeably accelerate exponentially after 2015, because the reflectivity of the glaciers themselves will have been compromised to the point that solar heating of the surface will begin to overtake their heat loss characteristic. The majority of glaciers will have disappeared from the planet by 2045, at current rates of loss.