Ice Caps and Sea Levels
The Connection Between Ice Sheets, Sea Levels, and Climate Change
The study of climate change, specifically global warming, naturally led scientists to the question of how increasing global temperatures would affect Earth’s ice. Research on glaciers, ice sheets, and ice caps has been ongoing for decades. Not all of the research has been to study climate change, of course. But over the years of study, scientists have recorded significant changes to ice on our planet. (See Featured Data.)
In the most comprehensive study to date, NASA scientists have confirmed that climate warming is changing how much freshwater remains locked in ice and snow. In a study published in the Journal of Glaciology, the study details the losses of ice and also the addition of new snow and ice over a decade. Using satellite mapping of the height of ice sheets and previous NASA airborne mapping data, scientists were also about to determine how fast the ice sheet is thinning.
Historically, there have been rises in sea levels on Earth. Global sea levels rose by approximately 120 meters in the years after the last ice age and then stabilized. Sea levels remained stabilized from then until the late 19th century. During the 20th century global average sea levels rose about 1.7 mm per year. Since the early 1990s satellite altimetry has provided even more accurate measurements. Those measurements show that sea levels rose at about 3.3 mm per year. At this rate climate models using the current rate of increase in greenhouse gases predict that sea level rise may reach 0.22-0.44 meters above the 1990 levels by 2090-2099. (IPCC 2007).
Briksdal glacier, Norway.
Snow cover melts during the spring and summer and is a seasonal process. Much of the melt flows into streams and rivers and eventually reaches the ocean. However, this amount would not significantly increase sea levels, although it might contribute to an overall effect if other factors come into play. Once sea ice and ice shelves are in the ocean (broken off from shorelines), they do not have a further influence on sea levels once they melt. Permafrost in tundra and pole regions may thaw with higher temperatures, but the water in the soil may not actually reach a stream, river, or the sea.
Melting ice sheets and glaciers have the most potential to significantly contribute to rising sea levels. The potential contribution of water from melted ice is thought to be uneven—the Greenland ice sheet may be contributing almost 30 percent while the Antarctic ice sheet may be contributing 10 percent. Complex ice dynamics may be the determining factor in ice flow rates.
Sea Level Rise Contributors
Comparison by volume (in white), by area (in gray), and by percent contribution (in red). Image courtesy of Meier et al., 2007.
Small Glacier and Ice Cap Contribution to Sea Levels
Amount of contribution (red line) and the annual global air temperature anomaly (blue line). Image courtesy of Mark Dyurgerov, Institute of Arctic and Alpine Research, University of Colorado, Boulder.