A paper in the Proceedings of the National Academy of Sciences this week calls to mind one of the most insidious aspects of global warming—it will take hundreds or thousands of years to see the full effects of the greenhouse gases. That’s because carbon dioxide stays in the atmosphere for hundreds of years and it takes a long time for oceans, ice sheets, and other parts of the worldwide climate system to change.
According to the Intergovernmental Panel on Climate Change, the sea level is expected to rise by less than half a meter by 2090 as glaciers and ice sheets melt and the warming ocean expands. The new study finds, however, that if temperatures go up by just one degree Celcius, sea levels will eventually—as ice sheet melt over the next 2,000 years—rise 2.3 meters. If temperature goes up 2 °C, oceans will rise 4.8 meters. If the planet warms by 4 °C, which is within the IPCC range of estimates, they will eventually rise by 9 meters, on average, and up to 12 meters in some parts of the world.
The point, aside from the fact that 12 meters is a lot of water, is that generations of humans will have to deal with sea levels that keep going up. And this is the case even if the more moderate predictions of temperature rise prove to be accurate. Decisions made now could have an impact long into the future (see “Climate Change: The Moral Choices”). The long term impact might make geoengineering options look more attractive (see “A Cheap and Easy Plan to Stop Global Warming”). Sulfate particles could shade the earth and help cool it off. Ultimately, it may be possible to accelerate the rate at which carbon dioxide leaves the atmosphere (see “Carbon-Capturing Rock”). But no one knows how well these approaches will work, or what side effects they might have.