The worst-case scenario for sea level rise is 6 feet (1.8 meters) by 2100, according to a new study. Unfortunately, this study is already out of date because it is based on expert opinion from back in 2012. This year, however, we’ve seen multiple bombshell studies on the growing prospect for West Antarctic Ice Sheet collapse — and similar findings that “Greenland will be far greater contributor to sea rise than expected.”
Even so, the plausible worst-case is important to understand because it is what should drive planning and “adaptation.” Also, avoiding the worst-case is typically a driving force behind prevention measures (people quit smoking because it might kill them or cause cancer) — in this case, slashing carbon pollution.
In fact, as the study points out, given a sufficient level of risk of high climate impacts, “no cost of mitigation is too high to justify.” Significantly, as the news release for the study notes, the major Fifth Assessment report (AR5) of the U.N.’s Intergovernmental Panel on Climate Change (IPCC) “was not able to come up with an upper limit for sea level rise within this century.”
There are five core contributors to warming-driven sea level rise, according to the study: (1)Thermal expansion, (2)Glacier ice loss, (3)Greenland ice loss, (4)Antarctic Ice loss and (5)Changes in land water storage. Thermal expansion is simply (ocean) water expanding as it warms up. Mountain glaciers that melt also contribute to sea level rise.
Also, large amounts of groundwater are “pumped for both drinking water and agricultural use in many parts of the world and more groundwater is pumped than seeps back down into the ground, so this water also ends up in the oceans,” contributing to sea level rise.
These three factors are relatively straightforward to estimate. The study uses the uncertainty distributions from the AR5 to determine the probability of different outcomes. But figuring out ice sheet loss in Greenland and Antarctica is more complicated, requiring knowledge of complex ice sheet dynamics that are not yet fully understood and modeled. So the authors “replaced the AR5 projection uncertainties for both ice sheets with probability distribution function calculated from the collective view of thirteen ice sheet experts” determined in a January 2013 study.
(Think Progress)
