Overview: Coastlines around the world are becoming increasingly crowded with both people and economic assets. At the same time, global sea-level rise is expected to increase the frequency and severity of costly coastal flood events. Managing the collision course between rising oceans and economic development is a grand challenge that society must address in the coming decades. I study how to make optimal use of the latest climate science to inform real-world policy and investment decisions that seek to manage the economic and social costs of sea-level rise.

What do coastal storms have to do with public policy?

Storm Damage Over Time

Coastal storms produce storm surge, a temporary anomalous increase in the height of the local water level that can cause dangerous and costly flooding. Over time, global sea-level rise will add to the baseline height from which storm surge has historically occurred, thus increasing the frequency of flood events. By the end of the 21st century, high-end projections suggest that global mean sea levels could rise by almost 2 meters (6.6 feet). Even the most conservative estimates indicate that the global mean sea level will rise over a foot. As such, the sea-level rise problem is inevitable. Rather than suffering from the negative impact of extreme flood events in the future, carefully designed public policy can encourage risk reduction strategies to emerge before a flood-related diaster occurs. The economic and social costs of sea-level rise will ultimately depend on our efforts to address the problem. Public policy is surely to play a major role.

The vastness of the coastal flooding public policy domain complicates effective change. Actors in several different disciplines participate and attend to considerations on different scales in space and time. My research focuses on just a handful of issues that are at play. Specifically, the questions I am currently trying to answer are (broadly):

1. How do international climate agreements (like the Paris Agreement) shape local coastal flood risk?

2. How do individuals make decisions involving current and future flood risk?

3. How do large governance structures (like major cities such as New York) make decisions on how to adapt to flood risk through so-called mega-infrastructure projects?

In investigating these questions, one encounters sometimes profound uncertainty in quantifying present and future flood risk. As such, I spend a good deal of time exploring how to optimally communicate these uncertain risks to different audiences looking to manage coastal flooding.

What international climate agreements mean for your flood risk

Future NYC Storm Surge

On the international stage, climate change accords, like the Paris Agreement, are undertaken between nations in an effort to reduce their emissions of greenhouse gases (such as carbon dioxide and methane) that warm the planet. Ultimately, how high the seas will rise will depend on by how much we limit the planet’s warming (that is, how much carbon dioxide we allow to remain in the atmosphere). On more local scales, a mayor of a coastal city may wonder what their future flood risk may be if the seas continue to rise. Connecting these two scales is important for informing local decision makers on how international agreements, which may be viewed by a local government official as inconsequential or vague, can impact conditions in their “backyard”. It may also motivate local actors to advocate for specific climate targets at the international level that could be beneficial for their community’s social and financial well being.

Future NYC Storm Surge

The Paris Agreement aims to keep the Earth’s global average temperature “well below 2 °C (3.6 °F) above pre-industrial levels” and to further “pursue efforts to limit the temperature increase to 1.5 °C (2.7 °F) above pre-industrial levels” (here, pre-industrial means the mid- to late-19th century—before coal and oil combustion were wide-spread). Given a temperature target (like 1.5 °C, or 2.7 °F), climate models can estimate how much global average sea-level rise may occur at some point in the future. However, very few coastal areas are expected to actually experience the global mean sea-level change. This is because the oceans are not like bath tubs. Due to many different earth system processes, the mean sea-level is not the same everyhere. Local projections of sea-level rise can vary significantly from the global average. Therefore, global projections of sea-level rise are insufficient for real-world decisions.

Sea-level rise projections for flood risk analysis

A flood frequency curve communicates how likely a flood of a given height is likely to occur, given the mean sea-level. Sea-level rise will dramatically reshape flood risk as it will increase the frequency of historical flood events (for example, how much higher is the historical 100-year flood in 2030 under uncertain sea-level rise?). Sea-level rise projections developed for coastal flood risk analysis should have three characteristics:

1. Sea-level projections should be specific to particular locations (i.e., local).

2. Local sea-level rise projections should span as full of a range of outcomes as possible. That means that they should consider both outcomes that are likely to occur and those that are unlikely to occur — given our current knowledge and understanding.

3. Local sea-level projections should made on timescales that are relevant for planning needs. For instance, 30-50 years for major infrastructure projects, and greater than a century for city planning.

Using sea-level rise projections to inform decisions

Complicated coastal flood risk projections produced by scientists and engineers are likely insufficient for most decision makers who require direct, “actionable”, flood risk information. For instance, a coastal homeowner may not find much use for technical, quantitative risk-related data. Rather, they may just want to know, “How high should I elevate my home to maintain my current level of flood risk?” Or a financial lending company may ask, “How high of a sea wall should we make our borrower construct around our asset to keep the annual level of economic damage constant?” Decision making frameworks can help a variety of end-users determine answers to these questions given uncertain projections of sea-level rise, all while incorporating 1) their level of confidence in climate projections, 2) their level of risk tolerance, and 3) their timescale of interest (for example, a 30-year mortgage or a 10-year municipal bond).

A near-term goal is to create free online tools that allow users to supplement their existing financial decision making frameworks with the latest climate information.

last updated: 5 July 2017

References

Buchanan, M. K., Kopp, R. E., Oppenheimer M., & Tebaldi, C. (2016). Allowances for evolving coastal flood risk under uncertain local sea-level rise. Climatic Change 137, 347-362. doi:10.1007/s10584-016-1664-7.

Deconto, R. M., & Pollard, D. (2016). Contribution of Antarctica to past and future sea-level rise. Nature, 531(7596), 591–597. http://doi.org/10.1038/nature17145

Kopp, R. E., Horton, R. M., Little, C. M., Mitrovica, J. X., Oppenheimer, M., Rasmussen, D. J., … Tebaldi, C. (2014). Earth’s Future Probabilistic 21st and 22nd century sea-level projections at a global network of tide-gauge sites Earth ’ s Future, 383–407. http://doi.org/10.1002/2014EF000239.Abstract

Tebaldi, C., Strauss, B. H., & Zervas, C. E. (2012). Modelling sea level rise impacts on storm surges along US coasts. Environmental Research Letters, 7(1), 14032. http://doi.org/10.1088/1748-9326/7/1/014032