IPCC: Sea Level Rise Adaptation Is Essential, Not Optional

The latest report from the United Nations Intergovernmental Panel on Climate Change (IPCC) hammers home, once again, that climate adaptation efforts are essential. "The growth in climate impacts is far outpacing our efforts to adapt to them," UNEP chief Inger Andersen warned prior to the report’s release. She urged nations, cities, businesses and individuals to turn adaptation efforts "into a sprint".

According to the IPCC, “The extent and magnitude of climate change impacts are larger than estimated in previous assessments.”

One of the impacts that is most evident and growing most quickly is sea level rise. By mid-century, one billion people will be exposed to much greater risks of flooding due to sea level rise. That exposure will result either from extreme weather, storm surges that roll in on the rising oceans, increased tidal flooding, or worse, permanent inundation. According to the IPCC, “this exposed population doubles at a 0.75m (2.5 feet) rise in mean sea level and triples at 1.4 m (4.6 feet) without population change and additional adaptation.” (see Summary for Policy Makers B.4.5)

The IPCC makes it absolutely clear that no amount of emissions reduction can stop the near and mid-term impacts of sea level rise. Even if we eliminated all carbon emissions today, sea level rise would continue in response to the warming that’s already occurred and how much we’ve already juiced our atmosphere.

But emissions reductions have enormous implications for how fast and how far sea levels will rise, particularly in the second half of this century and beyond. That’s why nations, including the United States, must place high priority on both climate adaptation and climate mitigation efforts.

According to a recent report from the National Oceanic and Atmospheric Administration (NOAA), global mean sea levels will rise at least a foot in the next three decades.  It took over a century of climate change for sea levels to rise that much to the present day.  

Think about that.  In the time it takes to pay off a 30-year mortgage, how many homes will be washed away?  

The effects of sea level rise aren’t just about flooding. Coastal aquifers will be vulnerable to salt-water intrusion, rendering them unfit for drinking water or agriculture. Drinking water drawn from coastal rivers may have to relocate their intakes as drop below the saline line.

And the impacts of sea level rise will fall hardest on those with the least capacity to adapt. Coastal communities and low-lying island nations are facing the threat of direct inundation as well as greatly magnified risks from storm surge, tidal flooding, and other modes of flooding.

How can we adapt to sea level rise?

Here in the U.S. there are several things that governments at all levels need to do…and do quickly.

  • Ramp up government investments in climate resilience and adaptation. We need Congress to pass President Biden’s Build Back Better agenda.  For dealing with sea level rise there’s funding to make flood insurance coverage more affordable for low-income households, include future sea level rise projections on official flood maps, and support adoption and enforcement of climate-smart building and zoning ordinances.   In November, Congress approved $50 billion for climate resilience programs, but much more is needed.   And this isn’t just a problem for the federal government. States also must do more to financially support climate resilience efforts – and many are, like New York, New Jersey, California, Florida, and North Carolina.
  • Engage residents in long-term planning efforts. The states and communities that engage their residents in honest discussions about sea level rise and the options for addressing the challenges will be much better prepared to implement equitable, long-term solutions (see Summary for Policy Makers C.1). As I told Grist.org, “If you want to wait until you’re in the middle of a disaster recovery operation to figure out your plan, you’ve already lost.”
  • Stop making your problems worse.  Every new home and business placed in a low-lying coastal area is one more home and business that will eventually have to be moved out of harm’s way. And the same goes for major infrastructure projects. These are among the maladaptive practices highlighted by the IPCC (see Chapter 3) that governments must cease.
  • Help at-risk people move to higher ground. A large proportion of people who live in low-lying coastal areas don’t have the resources to simply abandon their home and find a new one further inland. It’s essential that we provide government assistance to those who want to relocate (see Summary for Policy Makers C.2.12). But relocation assistance or a voluntary buyout can be maddeningly difficult to attain and the United States’ current efforts aren’t keeping pace with the demand.
  • Build with the future in mind. When development is allowed or infrastructure investments made, account for future sea levels. Most policies and permitting requirements fail to account for future conditions. Don’t make the mistake of only building to the minimum standards. 
  • Adopt policies that account for future sea level rise and flood risk. At every level of government, we’re largely failing to account for future climate impacts, including sea level rise. It’s increasingly important to factor sea level rise into every decision we make about where we build and how we build.
  • Consider all the options. There are many ways to address rising sea levels. Eventually, communities will employ multiple strategies -- buying out vulnerable homes, relocating infrastructure to higher ground, hardening critical areas that can’t be relocated.

Specific Adaptation Strategies for Sea Level Rise

Generally speaking, adaptation strategies for sea level rise fall into one of six categories illustrated in the figure below.

Strategies include doing nothing, Protect (seawalls, levees, etc.), Accomodate (elevating structures or insurance), Advance (building a buffer out into the ocean), Retreat (moving away from the coast), and Ecosystem-based Adaptation.

Source: Natural Resources Defense Council, 2019

Retreat and Ecosystem Adaptation

Retreat and ecosystem adaptation have some distinct advantages. Ideally, these strategies are best implemented together, in a complementary fashion. As we help people relocate to higher ground and unbuild previously developed areas, we create new land that can then be used for ecosystem-based strategies. However, these are the two strategies we have the least experience with, especially at the scale that sea level rise will require. Some of the benefits of these projects are:

  • It’s a one-and-done solution (at least for retreat). There is one guaranteed way to eliminate the risk of flood damage and that’s to make sure there is nothing at risk of flooding in the first place. Retreat is the only strategy that permanently eliminates the potential for future damages.
  • Retreat and ecosystem adaptation work together very well. Ecosystem-based strategies can require more open space than structural strategies, but when combined with managed retreat, that open space can be created over time.
  • Managed retreat affords the opportunity to also address legacy problems like social inequity and access to modern infrastructure and services. Retreat doesn’t just mean moving away from vulnerable coastlines. It can also mean moving towards a better place than the one people are leaving behind.
  • There are multiple opportunities to realize co-benefits with these types of projects. For example, ecosystem-based strategies not only can address vulnerabilities to sea level rise, but also create new habitat for wildlife, improve local water quality, or enhance groundwater recharge. If people are relocating to higher ground, it affords a community the opportunity to rethink where people live, where economic development should take place, and how roads, water, sewers, and other infrastructure can be improved and redesigned for the future.

There are certainly drawbacks to retreat and ecosystem-based strategies. They do raise a number of questions as to who pays and who benefits, as well as who is and isn’t going to get assistance to relocate.  These are not simple problems to solve, by any means. 

Protect, Accommodate, and Advance

The strategies of protect, accommodate, and advance will be widely used, especially in large coastal cities. But these strategies have some limitations, especially as sea levels approach or exceed the upper limits of our projections:

  • These strategies are dependent on making an initial assumption about how high sea levels will ultimately rise. For every six-foot seawall, Mother Nature will eventually serve up a seven-foot storm surge. Or Mother Nature will drop a foot of rain behind your seawall, flooding your city anyway.
  • These projects cost a lot.  Not only are they expensive to build, seawalls, levees, and surge barriers cost a lot to maintain and operate. According to an earlier IPCC report, “the bulk of the costs will be maintenance rather than capital costs.” Relying on structural solutions is a commitment to maintain these solutions forever.
  • These solutions tend to be one-dimensional, protecting against a single mode of vulnerability. A seawall may be effective against storm surge or direct inundation by rising seas, but if groundwater rises behind that barrier, that requires another solution (like massive pumps, which cities like New Orleans and Miami are now reliant on). Similarly, a solution that addresses salt-water intrusion may do nothing for flood risk.
  • Accommodation strategies (e.g., elevating roads or buildings, or relying on insurance to provide funding to rebuild) do not prevent flooding but reduce the potential for damage, make it easier to rebuild, or make living with the problem more tolerable.
  • Massive structural flood control projects introduce the problem of a single point of failure.  One failure anywhere along a levee negates the protective benefits for everyone that relies on the entire system. While they provide protection to the built environment, these options can contribute to other problems, like the loss of tidal wetlands, mangroves, and coastal natural areas.

There are numerous examples from around the world where these strategies have been successfully employed at scales small and large.  All of these climate adaptation strategies suffer from one current flaw: We typically don’t take action on them until after a major coastal disaster has already happened.

But all of these strategies (protect, accommodate, advance, retreat, and ecosystem-based strategies, as well as doing nothing at all) will be employed eventually, as individuals, communities, states, and the federal government and other nations come to grips with the reality of sea level rise.

About the Authors

Rob Moore

Senior Policy Analyst, Healthy People & Thriving Communities Program
Blog Post

Climate impacts are here and getting worse—so we can and must adapt starting now.

Blog Post

The latest IPCC (Intergovernmental Panel on Climate Change) report is an urgent call to adapt to the impacts of climate change. The risks and impacts of the climate crisis can be reduced, it says, “if humans and nature adapt to the changing conditions.” The Biden administration has two actions it could undertake soon in the face of growing twin threats of sea-level rise and extreme flooding: (1) update the National Flood Insurance Program, and (2) fully implement the Federal Flood Risk Management Standard.

Blog Post

Climate change is not off in some distant future: 2050 is less than 30 years away, and the tides are rising now.

Join Us

When you sign up you'll become a member of NRDC's Activist Network. We will keep you informed with the latest alerts and progress reports.