Assessing the Status of Alaska's Glaciers

New methods are providing an increasingly complex picture of a key contributor to global sea level. The glaciers of Alaska and northwestern Canada have long been considered important contributors to global sea level, but their remoteness has complicated efforts to quantify how their mass is changing. Nearly 30 years ago, the first regional assessment—based on data from only three glaciers and a largely intuitive regional extrapolation scheme—suggested that Alaska's glaciers accounted for more than one-third of the total sea-level contribution from glaciers and ice caps (excluding ice sheets) (1). Recently, global maps of water-mass variations, developed using satellite measurements of Earth's gravitational field (gravimetry), confirm with remarkable clarity the large role Alaska glaciers play in the global sea-level budget (see the figure). Far from solving the puzzle, however, these and other new observation technologies are revealing unexpected complexities in the magnitude and rate at which Alaska glaciers respond to climate.