Principal Investigator

Michael Oppenheimer

At a Glance

Probabilistic estimates of future sea level rise were developed with the help of detailed information about the Antarctic ice sheet. These estimates have been developed in collaboration with those engaged in coastal risk management against storm-driven flooding in several coastal cities around the world.

 

Research Highlight

The major uncertainty driving coastal risk management is the frequency of so-called “fat tail” probabilistic climate events, uncommon at the current time and in the past. However, sea level rise is leading to a gradual increase of this probability. According to some models, the current 100-year flood level could return with a yearly frequency by the year 2100. The Oppenheimer group’s studies show the uncertainty in the probability of such events is controlled by the future behavior of the Greenland and West Antarctic ice sheets, as they respond to global warming. At present, no reliable continental-scale process-based model for this behavior exists. This research program is developing alternative ways to project ice sheet behavior and sea level rise probabilities, in the absence of such a model. The program used methods combining multiple, independent lines of evidence to infer probabilities, including past measurements of ice sheet mass loss and regional-scale models of parts of the ice sheets, especially in Antarctica1,2.

A representative result is seen in in Figure 3.2. Panel (a) shows the projected sea level in 2100, in meters, under a commonly-referenced business-as-usual scenario for emissions. In northern Europe, values are notably lower than the Global Sea Level mean (GSL=0.79 m). The low values are due to the retreat of the Greenland ice sheet which reduces the gravitational pull of northern water toward Greenland and also produces crustal rebound—both effects offsetting some of the effect of ice loss. Panel (b) shows the uncertainty range for the estimate of sea level rise, also in meters. Estimates of the range are anomalously large in the same northern Europe region, reflecting uncertainties in the estimates of the ice sheet loss rate and in the resulting gravitational and crustal effects.

Figure 3.2. (a) Median projection and (b) width of likely range of local-sea level rise (in meters) for the year 2100 under the IPCC’s high-emissions scenario for representative concentration pathway RCP 8.51.

The program operates in collaboration with efforts in coastal cities around the world to plan risk management against higher sea levels. Oppenheimer is a member of the New York Panel on Climate Change, advising the New York City Mayor’s Office on how to build resilience in response to the increasing risk of climate change. This advisory role has resulted in a direct connection between the findings of this program and policy implementation. Other researchers at Princeton, such as Ning Lin of Civil and Environmental Engineering (also a member of the New York City Panel), have collaborated to implement the findings of this project for specific risk estimation methods that take into account flood damages, and the methods are now used by the city’s risk managers and planners. Interaction with New York City civic institutions reveals that climate risk management is only beginning to emerge as a continuous policy activity; planning and implementation of coastal reliance still lags far behind.

The next stage for this program will explore two different issues, critical to improving the utility of predictive modeling. (1) Other uncertainties in the basic calculation of flood probabilities will be explored: Sea level and storm intensity are not independent, yet current probabilistic methods treat them as such. The program will estimate the covariance of sea level and storm intensity, to refine flood probability estimates. Preliminary modeling suggests this effect is important. (2) Other lines of evidence will be included by a formalized methodology to produce a consistent approach to sea level estimation. In particular, an “expert elicitation” will be conducted.

 

References

  1. Kopp, R.E., R.M. Horton, C.M. Little, J.X. Mitrovica, M. Oppenheimer, D.J. Rasmussen, B.H. Strauss, and C. Tebaldi, 2014. Probabilistic 21st and 22nd century sea-level projections at a global network of tide gauge sites. Earth’s Future, 2(8): 383-406. doi:10.1002/2014EF000239.
  2. Little, C.M., R.M. Horton, R.E. Kopp, M. Oppenheimer, and S. Yip, 2015. Uncertainty in 21st century CMIP5 sea level projections. J. Climate, 28: 838-852. doi:10.1175/JCLI-D-14-00453.1.