Missions flown from the NASA base have documented some of the most dramatic evidence of a warming planet over the past 20 years: the melting of polar ice, a force contributing to a global rise in ocean levels.
Tidal waters worldwide have climbed an average of 20 cm over the past century, according to the 2014 National Climate Assessment. Why the seas rise? There are two main causes: first one the volume of water added to oceans from glacial melt and the second is the expansion of that water from rising sea temperatures. The oceans are absorbing over 90% of the increased atmospheric heat associated with emissions from human activity. Like mercury in a thermometer, water expands as it warms up (this is referred to as “thermal expansion”) causing sea levels to rise. Melting of glaciers and ice sheets is also contributing to sea level rise at increasing rates.
As the IPCC (Intergovernmental panel on Climate Change) prepares to issue a new report this fall, in which the sea-level forecast is expected to be slightly higher, gaps in ice-sheet science remain. But climate scientists now estimate that Greenland and Antarctica combined have lost on average about 50 cubic kilometres of ice each year since 1992—roughly 200 billion metric tons of ice annually. Many think sea level will be at least three feet higher than today by 2100. Even that figure might be too low.
In the last several years we’ve observed accelerated melting of the ice sheets in Greenland and West Antarctica. The concern is that if the acceleration continues, by the time we get to the end of the 21st century, we could see sea-level rise of as much as 2 meters globally instead of two to three feet. Last year an expert panel convened by the National Oceanic and Atmospheric Administration adopted two meters as its highest of four scenarios for 2100. The U.S. Army Corps of Engineers recommends that planners consider a high scenario of five feet.
One of the biggest wild cards in all sea-level-rise scenarios is the massive Thwaites Glacier in West Antarctica. Four years ago NASA sponsored a series of flights over the region that used ice-penetrating radar to map the seafloor topography. The flights revealed that a 600 meters high undersea ridge holds the Thwaites Glacier in place, slowing its slide into the sea. A rising sea could allow more water to seep between ridge and glacier and eventually unmoor it. But no one knows when or if that will happen.
By the next century, if not sooner, large numbers of people will have to abandon coastal areas in Florida and other parts of the world. Some researchers fear a flood tide of climate-change refugees. From the Bahamas to Bangladesh and a major amount of Florida, we’ll all have to move, and we may have to move at the same time. We’re going to see civil unrest, war. You just wonder how—or if—civilization will function. How thin are the threads that hold it all together? We can’t comprehend this. We think Miami has always been here and will always be here. How do you get people to realize that Miami—or London—will not always be there?