For years the ice sheets in Antarctica and Greenland were the most worrisome to climate researchers, because of their sheer mass. But it turns out the smaller ice sheets that dot the islands in the Canadian Arctic may play a larger role in sea level rise than anyone thought.

Alex Gardner, a research fellow in the Department of Atmospheric, Oceanic and Space Sciences at the University of Michigan led the project. He found that between 2004 and 2009 there was a rapid increase it the melting of the ice that sits on the thousands of small islands between Greenland and the North American mainland.

During the first three years of the study, the region lost an average of 7 cubic miles of water per year. That increased to 22 cubic miles of water -- roughly 24 trillion gallons -- per year during the last two years of the study. Over the entire six-year study period, this added 1 millimeter to the height of the world's oceans.

That may not sound like much, but Gardner notes that not all sea level rise is the same from place to place. New England, for example, will experience greater sea level rise than the Arctic, because as the ice melts weight of it is removed from the land, which rises.

The Canadian Arctic has only one third of the Earth’s land ice, and combined with the mountain glaciers in other regions accounts for half of the ice melt in the world. The other half is from the Greenland and Antarctic ice sheets.

Why the difference? Gardner notes that the sheer mass of the Greenland and Antarctic ice sheets plays a role – the larger a block of ice is the more energy it takes to melt. But as important is elevation. Both Greenland and Antarctica’s interior regions are thousands of feet above sea level, where temperatures are lower generally.

The smaller glaciers on the islands are not only putting more water into the ocean, they are also affected more strongly by high summer temperatures. Some areas, such as the southernmost parts of Baffin Island, may one day have no glaciers at all during the summer.

Gardner’s conclusions are drawn from a combination of modeling and data gathered from several institutions around the world.

Initially he used data gathered that measures the ice mass in several discrete locations in the Canadian Arctic. He then consulted with colleagues in Oslo, Norway, who used satellite-based laser altimetry to look at the height of the glaciers involved. Then he contacted colleagues in the Netherlands who had measured the Earth’s gravitational field by satellite. The three sets of measurements and the model Gardner used were in close agreement, giving Gardner confidence that his model and simulations were correct.

Gardner's results were published in the April 20 edition of Nature.