Last week, we looked at predictions for Global Sea Level Rise, GSLR, which average out to between 3 and 8 feet by 2100. The scientific consensus is that all contributions to GSLR can be traced back to increasing air temperatures, caused by the release of vast amounts of carbon dioxide from burning fossil fuels. Carrying on:
What's the role of Antarctica and Greenland in GSLR?
Between them, the Antarctica and Greenland ice sheets contain more than 99 percent of the freshwater ice on Earth. If all 7 million cubic miles of ice in Antarctica melted, sea levels would rise about 200 feet. For Greenland, the rise would be about 20 feet.
Is that likely to happen?
The bulk of Antarctica's ice lies on the high East Antarctic plateau, where the ice has an average thickness of about 7,000 feet. At this time, it looks relatively stable and may even be growing, since warmer oceans lead to greater evaporation and higher snowfalls. Of more immediate concern is the lower elevation West Antarctic peninsula and Greenland, where net outflows of fresh water into the world's oceans are occurring.
So what's happening in West Antarctica?
This region is Earth's canary in the coalmine because the air temperature there is rising faster than anywhere else: nearly five degrees Fahrenheit since 1960. Many glaciers or "ice streams" flow out from the peninsula, becoming free-floating ice shelves as they reach the ocean. Rising air temperatures lead to warmer seawater, which increasingly seeps under the West Antarctic ice shelves. The mechanism is self-reinforcing: The more the undersides of the shelves erode and melt, the more ice is exposed to warm water and the more melting occurs. As the biggest unknown in future GSLR, the fate of the West Antarctic ice shelves is the area climatologists are most concerned about. If the whole of the Amundsen Sea sector (see photo) were to melt — a real possibility given the latest data — global sea level would rise by about 4 feet.
What about Greenland?
Partial deglaciation, as it's called, is well documented in Greenland, where scientists have access to better data than in Antarctica, in terms of both history and accuracy. We know that the overall ice mass in Greenland is declining; for instance, between 1979 and 2006, summer melt increased by 30 percent over previous years, with a new record set in 2007. Of particular concern is the huge Jakobshaven glacier, which alone drains nearly 20 percent of all ice flowing from the interior to the sea. The Jakobshaven is currently retreating faster than any other glacier on Earth. During the last 10 years, it's lost 300 billon tons of ice, the equivalent of 11 years of normal Greenland snowfall. In a single dramatic incident two years ago — August of 2015 — it split off a chunk of ice that could cover Manhattan to a depth of 1,000 feet.
Even though it's difficult to make firm predictions, the takeaway from all this is that sea levels will continue to rise ever faster. With over 99 percent of climatologists convinced that humans are responsible for global warming, it behooves us to stand by the 2015 Paris climate accord by curbing our greenhouse gas emissions. The alternative is to condemn those who come after us to the consequences of our shortsighted inaction.
Barry Evans (firstname.lastname@example.org) sometimes wishes he could be the bearer of good news.