As the planet continues to warm, the ice sheets of Antarctica and Greenland are melting faster and faster, adding to sea-level rise. Scientists say even if the Paris climate agreement goals are met, melting from just the West Antarctic ice sheet alone could raise the oceans some 8 feet by the end of the century.
Even sooner, in less than 30 years, these ice losses will likely raise sea levels by 1 to 2 feet. And neither scenario factors in the impacts of thermal expansion of water already in the ocean and the melting of mountain glaciers, both of which are also contributing to rising ocean waters.
During the 20th century, sea levels rose about 6 inches, primarily due to thermal expansion and melting mountain glaciers, says Michael Oppenheimer, professor of geosciences and international affairs at Princeton University. Melting ice sheets did not make any significant contribution to sea-level rise until the last 15 years of the century.
Now, with melting ice sheets becoming a more common reality, the rate of sea-level rise is accelerating to about 12 inches per century, Oppenheimer says. But it won’t stay at that rate; it will continue to accelerate as ice sheets continue to melt.
“By the end of this century,” Oppenheimer says, “depending on which projections you look at, the rate of sea-level rise could wind up being about five times what it was…in the 20th century. And we're having trouble dealing with the 6 inches. We had trouble last century.”
“At this point, we're not ready for it. We're not primed to deal with it. We haven't deployed the adaptive measures that we really need to at the scope and rate that we need to."
Sea level rise at five times the rate as before will be awfully difficult to deal with, he says. “At this point, we're not ready for it. We're not primed to deal with it. We haven't deployed the adaptive measures that we really need to at the scope and rate that we need to. So this is a looming — not just a difficulty — but, in some cases, a disaster.”
Coastal communities, as well as governments, face several challenges in trying to cope with this reality. The first is that sea-level rise is happening “faster than people's ability to grasp what's going on and government's ability to mobilize and act,” Oppenheimer says.
Secondly, there is still some uncertainty about the behavior of the ice sheets. They could melt less or quite a bit more than predicted. The other big uncertainty is how much greenhouse gas the world will emit into the atmosphere in the next 20 to 40 years, which will determine how warm the planet will get and, therefore, how much ice melt and thermal expansion will occur.
“For the next approximately 30 years, we can say with fairly good confidence that we know what the sea level rise is going to be.”
“When you put all that together, what you see, interestingly, is that the difference in sea level rise projections between a lot of emissions and not too much emissions is not very much, until you get out to about 2040 or 2050,” Oppenheimer explains. “For the next approximately 30 years, we can say with fairly good confidence that we know what the sea level rise is going to be.”
In the US, we can expect that figure to be between 1 to 2 feet by 2050. While this may not sound like much, it’s enough to push beaches hundreds of feet back from the current shoreline and flood low-lying cities like Boston and New York, where many buildings are just a few feet above sea level.
“Add high tide to it and add a storm to it, and all of a sudden, you got a lot of flooding, just like happened in Hurricane Sandy,” Oppenheimer says. “Or, forget Hurricane Sandy — a big nor'easter. A nor’easter…does the same thing at a slightly smaller scale. So, we have a problem today. This isn't a problem for the future. This is what we failed to protect against adequately today.”
Among other things, Oppenheimer warns, “we are inevitably going to lose a lot of cultural heritage, because a lot of human cultural heritage is built right along the coast. And that's unfortunate. But it also means huge amounts of money lost. And it also means lives lost because people are caught unaware in big floods that happen now more and more regularly.”
As far as slowing or stopping the worst from happening, the solutions are pretty straightforward, Oppenheimer says.
“We’re always going to be behind if we don't implement very quickly a serious program to reduce emissions of the greenhouse gases, particularly carbon dioxide from burning coal, oil and natural gas, that are causing the problem in the first place."
“We’re always going to be behind if we don't implement very quickly a serious program to reduce emissions of the greenhouse gases, particularly carbon dioxide from burning coal, oil and natural gas, that are causing the problem in the first place,” he says. “As much adaptation as you do, climate change will always outrun it if you don't control greenhouse gas emissions. And as much greenhouse gas emissions as you control, it won't be enough to protect people unless we also do a significant amount of adaptation. So, we have to do both.”
“We need to build cities and other settlements smartly, so they're not so exposed to sea-level rise,” he continues. “There should be funding for building sea walls, surge barriers, whatever coastal defenses are necessary, where they're necessary; and there should be funding for facilitating people who make the choice to relocate away from the coast, or away from forest fire areas, or away from any area that's threatened by climate change.”