Sea level never stays still. Tides come in and go out – and vary within their cycles – and both land and sea levels rise and fall over time. The melting and expansion of the ice caps forms a significant component in this but the future contribution is difficult to predict. Now, a new study of Greenland’s glaciers may help to improve the accuracy of future sea level predictions.
Glaciers and Sea Level Change
We can express the balance between the earth’s ice (the cryosphere) and the oceans simply… perhaps over-simply. At times of high average global temperatures, the volume of the cryosphere reduces as ice melts, releasing water into the sea, causing the sea level to rise. Conversely, when the average global temperature is lower, more water becomes locked up in the ice caps rather than in the sea, and sea level falls.
Such variations occur naturally as the earth moves between warmer and colder periods. With fears regarding acceleration of global warming, come concerns that the rapid melting of the ice caps will have an impact upon sea levels, and on climate. (The addition of fresh water has the potential to affect ocean salinity, and alter ocean circulation – potentially influencing changes in global climate patterns.)
The Intergovernmental Panel on Climate Change (IPCC) notes that “glaciers and ice caps have experienced considerable mass losses, with strong retreats in response to global warming after 1970.” Estimates of the degree of change are, however, sometimes unrefined. As the most recent study, published today in Science, and entitled 21st century evolution of Greenland outlet glacier velocities notes, “large changes in ice dynamics … were not accounted for in early models and led to the inability to quantify uncertainty of 21st century sea level rise.”