Predicting Sea Level like Predicting Avalanches and Earthquakes
The most common question about sea level rise is ‘how high will it rise by when?’ It surprises many to learn that there is no way to predict that answer with any certainty. Also many mistakenly believe that projections for three or six feet are really the worst case scenario, which they are definitely not.
One of the ways that I explain our inability to predict when catastrophic sea level rise (SLR) could happen, is to use mountain avalanches as an example — though that surprises people at first. Many of us have been in areas of heavy snow and been told there is the “potential for an avalanche.” Yet there is absolutely no way to predict when an avalanche will occur. It could start in 3 days or 3 weeks, or NOT. There is simply no realistic way to model the complex dynamics of melting heavy snow mass to know when the structure will hit a critical point of failure. We accept that inability without questioning whether the scientific community is competent.
A slightly different metaphor is an earthquake. In spite of thousands of earthquakes to study, and putting sensors on known fault lines, we cannot predict an earthquake, despite tremendous effort over the last century to do so. For example seismologists in the San Francisco Bay Area were proud that they were able to issue a 10 second warning of a significant earthquake. (‘South Napa’ quake – August 24, 2014). Certainly that was valuable in that allowed some people to get out of elevators or buildings. Yet the fact is that we cannot really predict in advance how the pressures on the tectonic plates will suddenly shift. With earthquakes we can deduce statistical probabilities based on thousands of events but even those are framed in terms of decades. That is not the case with the collapse of the ice sheets.
The last time that there was a dramatic collapse of the ice sheets and glaciers was at least ten thousand years ago. The two great ice sheets are two or three miles thick. Like a potential avalanche there is no way to model exactly when they will collapse. When they collapse we will get many feet of SLR, in fact, eventually we will get tens of feet of SLR. The ice sheet on Greenland holds the equivalent of 24 feet (7 meters) of SLR. Antarctica is 186 feet (56 meters). It will take centuries or millennia for that to fully happen. Our very real challenge is to begin to plan for the range of scenarios for what can happen in the middle of this century and into the next.
Because scientists cannot predict whether that will happen by the year 2100, or in the following century, that potential is generally omitted from the SLR projections. Scientists need to be able to cite objective data, based on measurements that can be verified. The collapse of the glaciers and two great ice sheets do not fit that requirement. In my consulting work, I help those that are interested in big strategic planning to look at multiple scenarios, producing a range of possibilities, recognizing that we cannot know the actual numerical probabilities.
We need to explain this better. People, communities, companies, and governments need to understand that we are going to get tens of feet of sea level rise sometime in the next few centuries. In the second half of this century we could start to see catastrophic SLR. Now is the time to do strategic planning. One way to explain the misleading or misunderstood limitations about rising sea level may be the uncertainty of mountain avalanches and earthquakes.
We design buildings for the possibility of severe earthquakes despite the uncertainty. We need to take a similar approach to the inevitable sea level rise that is now in our future. Like avalanches and earthquakes, the smart attitude is to do full range scenario planning. In the case of sea level rise, it is not a matter of “if”, but rather how high, how soon.