"The oceans and ice are in trouble. If they're in trouble, we're in trouble because we depend on them."
- Prof. Michael Oppenheimer

As global average temperatures increase, runoff from melting mountain glaciers, melting and disintegration of ice sheets, and thermal expansion of warming ocean water will cause additional sea-level rise. Coastal flooding happens when a storm raises the level of the sea further and pushes the water inland, and other types of flooding can occur during particularly high tides. Both types of high water events will occur much more frequently in the future because they start from a higher baseline sea level. What had been considered "100-year flooding events" are expected to occur annually or even more often in many places by 2050.

More frequent flooding has a number of economic, environmental, and human costs. Our researchers are developing approaches for better estimating and planning for the potential effects of sea-level rise under different warming scenarios, particularly given the rapid acceleration of the ice sheet contribution. They are also analyzing political decision-making regarding large infrastructure projects that could help mitigate the effects of sea-level rise.

The Ocean and Cryosphere in a Changing Climate - IPCC Report

Oceans cover nearly 3/4 of the surface of the earth, and are a critical part of Earth's complex climate system. Oceans, along with the cryosphere (a term that refers to all of the frozen parts of the Earth, including glaciers, ice sheets, sea ice, snow cover, and permafrost), provide important resources that help sustain life on Earth and also play a key role in regulating climate and weather. Global warming has caused melting of the cryosphere, contributing to sea-level rise. This increase in sea level will have a particularly devastating effect on coastal and island communities, which will be more susceptible to regular flooding and extreme weather events.

While some of the worst effects can be slowed or lessened with deep and rapid cuts in greenhouse gas emissions, some degree of sea-level rise in the coming decades and centuries in unavoidable. This report of the Intergovernmental Panel on Climate Change (IPCC) includes assessment of the current expected sea-level rise, projections of future risk, and an exploration of possible responses, including adaptation actions that can be taken to cope with sea-level rise. Policymakers will have difficult choices to make - ones that involve forethought, careful planning, dedicated resources, and sensitivity to the serious governance challenges involved. The report outlines five categories of responses, exploring them in detail:

1. Protection of the coast by blocking inland water movement (e.g. levees, bulkheads, surge barriers)
2. Accommodation of sea-level rise by altering structures and activities to make them less vulnerable to sea-level rise (e.g. raising homes on stilts, utilizing salt tolerant crop varieties, changing zoning regulations to create buffer zones)
3. Advance by reclaiming and building up the shoreline
4. Retreat through moving people, assets, and activities away from the shoreline
5. Ecosystem-based adaptation, restoring critical coastal ecosystems that can help slow flooding, such as beaches, wetlands, and coral reefs

Find the full IPCC report with the Summary for Policymakers here.

Chapter 4 Lead Coordinating Author: Prof. Michael Oppenheimer

Coastal Flood Protection Design

Analyses of how Antarctica will respond to a warming planet embody large uncertainties that increase with time. As such, future projections of sea-level rise are strongly dependent upon expert judgment about how much and how quickly Antarctica will melt. This uncertainty complicates any decisions regarding how high to build flood protections in order to reduce coastal flood damages from rising sea levels. Generally, the higher the structure, the greater the margin of safety afforded. If the prescribed margin of safety does not properly account for sea-level rise and its uncertainties, the effectiveness of the flood protection will decrease over time. This could potentially waste money and put lives and property at greater risk.

Our researchers have developed a decision-making approach for flood protection designers that allows them to calculate the height of various flood protection strategies based on their risk tolerance with respect to future Antarctic melt. This framework is compatible with existing decision making protocols such as those used by the U.S. Army Corps of Engineers.

Researcher: D.J. Rasmussen

The Politics of Climate Change Adaptation: Storm Surge Barrier Implementation

Increasing global average sea-level rise is already contributing to shorter windows of opportunity for recovery between costly and deadly coastal floods in some urban areas. In response, some cities — like New York City — are proposing to construct large, multi-billion-dollar structural coastal defense “megaprojects” to protect targeted areas during extreme high-water events (e.g., coastal storms). Historical experience has shown that efforts to construct large coastal defense projects face political obstacles in their implementation. These include: navigating existing governance structures and institutions, competing with multiple project proposals, managing potential liability, and financing.

Our researchers are seeking to understand how levels of support and opposition from government agencies, elected officials, and the general public influence the likelihood of a large coastal defense infrastructure project reaching completion. 

As part of this qualitative research project, our researcher is also making a short film that discusses storm surge barriers as potential solutions to New York City's flood problem.

Researcher: D.J. Rasmussen

Sea-Level Rise Projections

Sea-level rise is magnifying the frequency and severity of extreme sea levels that can cause coastal flooding. The rate and amount of global average sea-level rise is directly linked to the trajectory of global average surface temperatures. Therefore, temperature stabilization targets (e.g. 1.5 °C and 2.0 °C of warming above pre-industrial levels, as from the Paris Agreement) have important implications for coastal flood risk.

Our researchers assess the differences in the expected frequencies of extreme sea levels across scenarios that stabilize surface warming at 1.5 °C, 2.0 °C, and 2.5 °C and determine projected sea level rise at each level. They further examine the impact of sea level rise for different regions, including the eastern United States and small island nations. 

Resource: D.J. Rasmussen, K. Bittermann, M.K. Buchanan, S. Kulp, B.H. Strauss, R.E. Kopp, and M. Oppenheimer, 2018: Extreme sea level implications of 1.5 °C, 2.0 °C, and 2.5 °C temperature stabilization targets in the 21st and 22nd century. Environ. Res. Lett. doi:10.1088/1748-9326/aaac87

Researcher: D.J. Rasmussen, Prof. Michael Oppenheimer