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Sea Level Rise Is Accelerating

Paul Kando

For years, computer simulations by the Intergovernmental Panel on Climate Change (IPCC), NASA, and the European Environmental Agency have projected at least 2 feet of average global sea level rise by the end of this century, compared to 2005 levels. Using satellite data, a new study, Climate-change–driven accelerated sea-level rise detected in the altimeter era, published in the Proceedings of the National Academy of Sciences (NAS) last February confirms those projections.

Dramatization of sea level
photo credit: Anthropecene Magazine

As the planet warms, the oceans rise faster. The rate of sea level rise is accelerating so fast that some coastal and tidal communities — such as our own — could end up with an additional 4 inches per decade by the end of this century.

Storm surges will increase erosion and damage homes, businesses and transportation infrastructure. Seawater may spoil freshwater aquifers. Many island nations and large swaths of South Asia will lose precious land where people live and grow their food.

The NAS study assumed a steady acceleration of the rate observed over the past 25 years, measured by the ocean-scanning radars of satellites, which paint a 3D picture of the fluctuations of the oceans' surface. But the changes could happen much faster than they have so far. If global warming speeds up the melting of the ice sheets and glaciers of Greenland and Antarctica (as discussed in last week’s column), a 2-foot rise could turn out to be the minimum by end of century.

By analyzing data from a series of international satellite missions since 1993, the scientists were able to distinguish the greenhouse gas fingerprint from natural variations caused by volcanoes and El Niño cycles. The detailed radar altimeter readings used in the study cover entire oceans. They clearly show the fluctuations of the sea surface, caused partly by the expansion of warming water and, increasingly, by the massive inflow of melting ice from Greenland and Antarctica.

Combined with analyses of years of sea level data from coastal tide gauges and ice sheet stability research, scientists can now create a detailed picture of how sea level rise will affect coastal communities in great detail. The new study is noteworthy because it relies completely on observational data, which show good agreement with earlier climate simulations. Folks who don’t want to do anything about climate change because they “don't trust computer simulations” must now find some other excuse.

The European Environmental Agency recently issued an update of their sea level information with similar figures, documenting a sea level rise of 3 millimeters per year—clearly much above the IPCC’s 20th century average of 1.8 millimeters per year.

Germany and the Netherlands have already incorporated the most recent accelerated sea level rise projections into their coastal planning, and NASA's January 2018 update for the U.S. does the same. Recognizing the acceleration is particularly urgent for vulnerable communities in low-lying coastal zones, islands and delta regions, which may need international help to adapt.

Some scientists warn that a rapid disintegration of the Antarctic ice sheet could push sea level up even faster and higher — by as much as 4 to 10 feet by 2100. That would certainly flood large parts of our coastal communities, from Portland to Bath, to Rockland, to Main Street Damariscotta.

The last time Earth was as warm as it is now — 125,000 years ago — the average sea level was 6 meters (19.7 feet) higher than it is today. The big question is, how long will it take to get there again. If adaptation and mitigation fail to keep pace, damage from storm surges and extreme rains is certain to increase. Even if they already know they're at risk, cities and towns may not be able to adapt fast enough without major additional investments in resilience and disaster relief.

Will the US government catch on? Disaster relief provisions in the latest federal spending bill include some funding to make communities more resilient to the long-term threat of climate change — the kind of money we should be investing every year, not just after major hurricanes. Failing to invest in adapting to anticipated long-term sea level rise, means remaining behind the curve. It may also mean an upcoming international refugee crisis compared to which the current one is but a picnic in the park.

Hurricane recovery funding, too, must take future flood risk into account. FEMA should ensure that damaged homes, businesses and infrastructure are rebuilt to higher standards than those required by local construction laws. All federally funded infrastructure projects must be designed to stand up to the increasing flood risk from global warming.

I know my town, Damariscotta, needs to be better prepared. What about yours?