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Sea Level Rise Is Accelerating: 4 Inches Per Decade (or More) by 2100

Satellite data confirm what computer models have warned for years: Oceans are rising faster as the planet warms, and coastal communities face increasing flood risk.

Rising sea levels increase the risk of storm surge flooding in coastal cities like Charleston, South Carolina, shown here after Hurricane Matthew. Credit: Brian Blanco/Getty Images

The rate of sea level rise is accelerating so fast that some coastal communities could confront an additional 4 inches per decade by the end of the century—a growing concern now confirmed by thorough measurements from space.

At that rapid pace of change, vulnerable communities might not be able to keep up. Storm surges will increase erosion and damage homes, businesses and transportation infrastructure in some areas. In other places, seawater will intrude on freshwater aquifers. In South Asia and the islands, people will lose the land where they live and farm. And the changes will arrive much faster than they do today.

Scientists have been warning about this speed-up for many years based on computer climate simulations. A new study released Monday confirms the modeled trend with a detailed analysis of satellite observations spanning a quarter of a century.

The findings, published in the Proceedings of the National Academy of Sciences, reinforce the outlook that average global sea level is likely to go up at least 2 feet by the end of this century compared to 2005 levels.

The study confirms that the Intergovernmental Panel on Climate Change (IPCC), NASA and the European Environmental Agency were correct when they found that the rate of change had increased in recent years.

And if the rate of acceleration intensifies—as it might if global warming speeds the melting of the Greenland and Antarctic ice sheets and glaciers—a 2-foot rise might be the low end of the likely range. The study assumes a steady acceleration at only the rate observed in the past 25 years.

The satellites' ocean-scanning radar paint a 3D picture of the oceans' bulges and dips. The findings are a "game-changer" for the climate discussion, said University of South Florida climate researcher Gary Mitchum, who co-authored the study with a team of scientists across the country.

Even cities that already know they're at risk may not be able to prepare fast enough without additional investments in disaster relief and resilience. That includes Tampa, where his university is based. The city has been listed as one of the 10 cities globally most vulnerable to sea level rise. If the rates of adaptation and mitigation don't keep pace, damage from storm surges and extreme rains is likely to increase.

Building Resilience into Hurricane Recovery

Congress may be catching on, said Rob Moore, a policy analyst with the Natural Resources Defense Council. Disaster relief provisions in the federal spending bill approved on Friday include significant funding to make communities more resilient to the long-term threat of climate change.

"I'd say this recent budget deal is encouraging, but it's a one-time thing," Moore said. "This is the kind of money we need to be investing every year, not just after major hurricanes. It's a symptom of a cycle we need to get out of. The only time we invest is after a major disaster. Until the country invests in adapting to long-term sea level rise, we will always be behind the curve."

Moore highlighted provisions that would enable FEMA to rebuild damaged homes, businesses and infrastructure to higher standards than those required by local construction laws.

Last summer, President Trump raised concerns when he rolled back an Obama-era rule requiring that federally funded infrastructure projects be designed to stand up to the increased flood risk from global warming. Last week, however, the Department of Housing and Urban Development issued guidelines for the spending of hurricane recovery funds that require taking future flood risk into account.

A Surprisingly Detailed View of the Risk

The new study adds to the evolving field of sea level science by picking apart a wealth of data from a series of international satellite missions starting in 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, showing the fluctuations in the sea surface caused partly by expansion of warming water and, increasingly, from the massive inflow of melting ice from Greenland and Antarctica.

Combined with analyses of long-running sea level data from coastal tide gauges and related research on ice sheet stability, scientists can now create a surprisingly detailed picture of how sea level rise will affect coastal communities, even down to the neighborhood level, as shown in these NOAA maps.

Lead author Steve Nerem, a sea level expert at the University of Colorado, Boulder, said the new study is notable because it relies completely on observational data, which shows good agreement with computer climate simulations.

"Some folks have not wanted to do anything about climate change because they don't trust the models. These findings support the modeled projections," he said.

3 Millimeters a Year and Accelerating

"All available assessments agree that an acceleration is detectable," said Hans-Marin Füssel, a climate impacts project manager for the European Environmental Agency, which issued a recent update on sea level with similar figures showing a current sea level rise of 3 millimeters per year. During the 20th century, average global sea level rose about 1.8 millimeters per year, according to the IPCC.

"That's a clear acceleration over the 20th century trend," Füssel said.

Germany and the Netherlands have both incorporated the most recent projections of accelerated sea level rise into their coastal planning, and he said that NASA's January 2018 update for the U.S. uses similar projections.

Sally Brown, a sea level rise expert at the University of Southampton in the UK, said recognizing the acceleration is particularly urgent "for vulnerable communities in low-lying coastal zones, such as small island or delta regions, who may struggle to adapt without international help."

Some scientists also warn that a rapid disintegration of Antarctica's ice sheets could push sea level up much faster and higher, by as much as 4 to 10 feet by 2100.

"The largest uncertainty is really Antarctica," said Ingo Sasgen, a climate researcher at the Alfred Wegener Institute in Germany. "The big question for planners is how to deal with the possible extremes."

The last time Earth was as warm as it is now was about 125,000 years ago, and we know sea level was 6 meters higher than it is today, Nerem said. "The big question is, now long will it take to get there."

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