It could take a few hundred years or even 2,000 but the eventual, permanent flooding of low-lying areas in Sacramento is guaranteed if greenhouse gases are not deeply reduced, according to new research.
A rising sea level due to climate change is expected to dramatically alter the future landscape of many of the world's coastal areas around the world. A new study shows that the largest U.S. cities highly threatened by future sea level rise are Miami, Virginia Beach, Va., Jacksonville, Fla., and Sacramento.
While Sacramento is not a coastal city like the others, its numerous waterways make it particularly vulnerable.
The flooding could take centuries, depending on the rate of future emissions and ice melt in places like Greenland. A 5-foot rise would be inevitable in the Sacramento area, even with deep cuts in emissions, experts say. California's capital would be affected by a sea level rise working its way up the Sacramento River.
The level of accumulated carbon in the atmosphere, emitted by two centuries of burning fossil fuels, already guarantees several feet of sea level rise, the experts say.
A peer-reviewed study in the current issue of Proceedings of the National Academy of Sciences concludes the Earth is already "committed" to 7.5 feet of sea level rise in the next 2,000 years, assuming a conservative 1-degree Celsius increase in global temperature.
The study was led by Anders Levermann at the Pottsdam Institute for Climate Impact Research in Germany and includes co-authors in the United States. It was funded by grants from the German government and the National Science Foundation in the United States.
In the same journal, researchers at Climate Central, a nonprofit educational group in New Jersey, took the research a step further. By combining the sea level predictions with land elevation data, they estimated which U.S. cities will eventually be flooded.
One of those cities is Sacramento. In particular, the city's Pocket neighborhood will be flooded if 7.5 feet of sea level rise occurs. Parts of Natomas will also go under, particularly neighborhoods along Truxel Road.
These areas are also forecast to flood with a smaller sea level rise as little as 2 feet in the case of the Pocket.
The group acknowledges many uncertainties. One is that the elevation data used in the analysis don't account for levees or future engineering solutions.
In other words, existing levees could protect these neighborhoods in the early phases of sea level rise, when water levels increase 1 to 3 feet. Beyond that, and certainly at the predicted 7.5 feet, levees might not help, though they could be raised to avoid inundation.
The Climate Central analysis is dubbed a "commentary" in the journal and was not peer-reviewed.
The conclusion is that a significant share of Sacramento's population lives on land that will be underwater in a few hundred years 2,000 years at most if global carbon emissions aren't deeply cut.
"It could be a great deal sooner," said Benjamin Strauss, author of the commentary and a scientist at Climate Central.
One reason for the uncertainty is that the "worst-case scenario" of emissions is now considered to be conservative. Developed in 2000, the scenario was the highest possible future rate of emissions agreed on by an international panel of scientists. Many scientists now recognize emissions have actually exceeded this worst-case scenario, meaning it could underestimate how fast the climate is changing.
But that doesn't mean there isn't time to slow climate change with lower global emissions, Strauss said. A world with lower emissions could reduce impacts substantially by almost threefold.
California is "leading the way in "transitioning to power from renewable and non-carbon sources," said Richard Wiles, director of research at Climate Central.
However, Wiles emphasized that Climate Central does not lobby or advocate on policy. "We don't take any opinion on how they do it," Wiles said.
If the current trend of global carbon emissions continues unabated, Sacramento is one of several large U.S. cities that will be "locked-in" by the year 2100 to a future under the sea, Climate Central says.
Locked-in means "there's nothing you can do about it," said Wiles. "It's like when you put an ice cube on a table, I can guarantee you it will melt completely I just can't tell you exactly when."
The research by Levermann produced an ice-sheet melting rate for Greenland and Antarctica. This has been troubling to estimate in the past but is critical to estimates of sea level rise because these ice sheets hold huge quantities of water.
Climate Central paired this melting rate with new data from the National Oceanic and Atmospheric Administration measuring the elevation of coastal cities to within a few inches.
"What they're trying to do is make the science understandable, which is really important," said Chris Field, a climate researcher at Stanford University who was not involved in either study. "It's important because people need the information to make intelligent decisions."
Scientists estimate that complete melting of the Greenland ice sheet alone would raise sea level 23 feet, which could be a global catastrophe since nearly one-third of the world's population lives in a coastal zone. This includes Sacramento, which is effectively on the coast of a vast tidal estuary.
"What would you recommend if there was 23 feet of sea level rise?" wondered Francis Chung, an expert on climate modeling at the California Department of Water Resources. "I say pack and run. That's unthinkable."
Chung said his department has been planning for a sea level rise of about 4 feet, the maximum California scientists expect by 2100.
He noted another uncertainty in the new research, also acknowledged by the authors, which is that sea level rise will vary around the world due to geologic factors. One example, Chung said, is the California coast near Eureka, which is slowly rising because of earthquake fault activity. As that occurs, it counteracts sea level rise to some degree. Other areas, like the Delta, are subsiding, which will make sea level rise worse.
Such factors make exact predictions challenging on a local level.
"Sea level is rising. It's a fact. It has risen already," Chung said. "But how far will it go? What should we plan for? That's where the confusion begins."
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