Photo: NCDOT Communications/Flickr
When trying to figure out just how much higher the world's oceans will be by the end of this century, studies can give a wide range of estimates. Even if something around three feet looks likely at this point, there are still a lot of variables. One thing is certain though: what we set in motion today, through rising emissions of greenhouse gases, rising temperatures and melting ice, will continue to have an effect on the sea-level far into the future.
A new study from the Potsdam Institute for Climate Impact Research, published in Proceedings of the National Academy of Sciences, attempts to give some clarity to what we can expect in the coming centuries and millennia, thanks to rising temperatures.
In short, the study finds that for every degree the climate warms, we are likely to lock in at least 6 feet of sea level rise—obviously that happens over time, as the melting global ice sheets that will contribute most to the rising oceans are somewhat delayed in responding.
Looking at a 4˚ C rise in temperature, something which increasingly looks certain (due to collective inaction to constrain greenhouse gas emissions and a far too-slow effort to transition off fossil fuels), the study found that, over the next two millennia, the melting Antarctic ice sheet will contribute 50 percent of the sea level's rise, melting Greenland will contribute 25 percent, thermal expansion of the oceans contributes 20 percent and melting glaciers account for the remaining 5 percent.
Previous research, also coming from the Potsdam Institute, found that if temperatures rise continues past 2˚ C, there's a greater than 50 percent chance that the Greenland ice sheet will melt, causing over 20 feet of sea level rise, over the next 300-1,000 years.
Melting in Antarctica contributes less than 10 percent to sea level rise today. The seemingly low amount that glaciers will contribute can be attributed to the study's long-term view of sea level rise – by the time Antarctica is contributing to the sea, half of the world's glaciers will have already melted back to their minimum level.
Over the past century, global sea level has risen a bit under 8 inches. Since the Industrial Revolution, global average temperature has risen 0.8° C, though regionally there are some dramatic variations from that.
Study lead author Anders Levermann gets at the crux of the issue, from the standpoint of what we need to plan for:
Continuous sea level rise is something we cannot avoid unless temperatures go down again. Thus we can be absolutely certain that we need to adapt. Sea level rise might be slow on time scales on which we elect governments, but it is inevitable and therefore highly relevant for almost everything we build along our coastlines, for many generations to come.
Despite dramatic simulated images and slideshows depicting swamped US cities, in terms of accurately portraying how sea level rise will damage urban environments, the reality is far messier. Even with small levels of sea level rise–smaller than what's predicted over the next 100 years even–the slideshows ignore what this Potsdam research is describing on a longer time scale: namely that storms will get more destructive. This is what will start driving people back from the coasts far before city and town streets get actually, perpetually submerged.
Sea level rise really looks like destruction from hurricane-force winds and moving shorelines, not some seaside boardwalk and abandoned buildings placidly submerged. The scariest part is that even though we see it coming, we're still marching right into it.