Sea level rise is one of the most feared consequences of global warming.
Polar ice caps and mountain glaciers are melting at such an alarming rate, that scientists don’t seem to agree how many meters the sea level will rise and how fast it will happen.
The Intergovernmental Panel on Climate Change worst case scenario predictions were of less than 1 m of sea level rise by the end of the century, but apparently they were way too optimistic. Recent studies suggest that the IPCC global sea level rise predictions were seriously underestimated.
The two major ice sheets that will most likely cause sea level rise (when melted) are Greenland and the West Antarctic Ice Sheet. But the amount of ice that will melt and the time it will take it’s still unknown.
Greenland is the world’s largest island, with an area of over 2 million square kilometers. Most of the island is covered by an ice cap that can reach thicknesses of 3 kilometers
Data from a NASA satellite shows that the melting rate has dramatically accelerated since 2000.
If the ice cap were to completely disappear, global sea levels would rise by 6.5m.
Estimated monthly changes in the mass of Greenland’s ice sheet suggest it is melting at a rate of about 239 cubic kilometres per year. Most scientists agree that the melting won’t be gradual, there will be a tipping point when the melting will abruptly accelerate. When will this happen is still unknown.
National Snow and Ice Data Centre
We have known about Greenland’s dangerous warming for a while, but we recently learned that Antarctica is no longer immune to global warming.
A very recent study (Mann, et. al) published in Nature magazine, shows the increased and abrupt warming of the West Antarctic Ice Sheet. Mann explains that “a larger part of West Antarctica is melting than previously thought”.
In stark contrast, a large part of the continent — the East Antarctic Ice Sheet — was found to be getting colder. The cooling was linked to another anthropogenic (human-caused) effect: ozone depletion.
The West Antarctic Ice Sheet (WAIS) is 1,800 meters above sea level and holds approximately 2.2 million cubic kilometers of ice, about the same amount of ice contained in the Greenland Ice Sheet.
Jerry Mitrovica, co-author of a new and groundbreaking study (published in Science) explains that “The West Antarctic is fringed by ice shelves, which act to stabilize the ice sheet — these shelves are sensitive to global warming, and if they break up, the ice sheet will have a lot less impediment to collapse”.
Whether or when this ice sheet might collapse and melt is still very uncertain, but even a partial melt would have a bigger impact on some coastal areas than others.
Sea level rise will not happen uniformly around the globe. When physical and gravitational factors are applied to projections of sea level rise, the impact on coastal areas is dramatically worse in some parts of the world than predicted so far.
The Intergovernmental Panel on Climate Change (IPCC) estimates that a full collapse of the WAIS would raise sea levels by 5 meters globally.
Mitrovica explains that this is an oversimplification, and that sea level rise will be higher than expected, and greater in some places than in others (such as North America).
This study shows three important factors that the IPCC overlooked:
Gravity: Huge ice sheets exert a gravitational pull on the nearby ocean, drawing water toward it. If an ice sheet melted, that pull would be gone, and water would move away. In the case of the West Antarctic Ice Sheet, the water would move away from the south towards northern latitudes.
Rebound: The WAIS is called a marine-based ice sheet because the weight of all that ice has depressed the bedrock underneath to the point that most of it sits below sea level. If all, or even some, of that ice melts, the bedrock will rebound, pushing some of the water on top of it out into the ocean, further contributing to sea level rise.
- Earth’s rotation: A collapse of the WAIS would also shift the South Pole location of the earth’s rotation axis from its present location. This would shift water from the southern Atlantic and Pacific oceans northward toward North America and the southern Indian Ocean.
Mitrovica explains that “The net effect of all of these processes is that if the West Antarctic Ice Sheet collapses, the rise in sea levels around many coastal regions will be as much as 25 % more than expected, for a total of between 6 and 7 meters if the whole ice sheet melts,”. That’s a lot of additional water, particularly around such highly populated areas as Washington, D.C., New York City, and the California coastline.
“We aren’t suggesting that a collapse of the West Antarctic Ice Sheet is imminent,” said study co-author Peter Clark of Oregon State University. “But these findings do suggest that if you are planning for sea level rise, you had better plan a little higher.”
Click here for a great interview with the researchers of this amazing study.
If you want to see different scenarios of sea level rise in your area go to Google Flood Maps, select 5-7 m and zoom in your home town to see if in the next 100 years your home will be under water!