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Study says coastal cities could escape some flooding if carbon emissions are cut sharply

Delaware Public Media file

Delaware cities like Wilmington, New Castle and Dover could avoid the worst effects of long-term sea-level rise if global carbon emissions are sharply reduced, according to a study released on Monday.

The study by Climate Central, a research group based in Princeton, NJ, looked at the areas of coastal cities around the country that would be flooded under different concentrations of greenhouse gases in the next century.

Although a certain degree of inundation is locked in because of historic and current carbon emissions, low-lying areas and their populations could escape the most severe consequences of rising seas if policymakers make radical carbon cuts, the study said.

In Dover, for example, about 8,000 people -- based on 2010 census data – live in areas that would be below the high-tide mark at some point in the future if carbon emissions remain about the same as they are now.

But the Dover population exposed to flooding would fall sharply to only around 250 under a scenario of “extreme” carbon cuts – requiring policy changes like large-scale switching to renewable fuels and/or more adoption of nuclear power.

In Wilmington, some 8,500 people in the 2010 census lived in areas that would be flooded at high tide if carbon emissions are not cut, but that number drops to about 3,800 under the study’s low-emissions scenario.

And in New Castle, land that was home to about 3,000 people would be spared flooding if emissions were cut to the lowest level, the study found.

It acknowledged that most climate projections, such as those issued by the State of Delaware, expect ocean levels to rise by about 1 meter from current levels by 2100.

Although 1 meter of sea-level rise would have devastating effect on Delaware, inundating 8-11 percent of its land mass, according to the official forecast, the increase in the next century could be much greater -- perhaps as much as seven times greater -- because of past and current emissions, the report said.

Susan Love, who heads planning for climate change and mitigation at Delaware’s Department of Natural Resources and Environmental Control, said she had not studied the Climate Central report in detail but agreed with its conclusions that sharp carbon cuts are needed to avoid the worst effects of future sea-level rise.

“If we do not move to reduce our carbon emissions, then the type of future they have discussed in this report is likely at some point,” Love said.

“The places that we are living in today, that feed our national economy and feed our quality of life are very much at risk,” Love said. “If sea levels rise to a certain point, there will be very few things people can do to adapt, and people will have to move away from the coast to the new coast, which will be much further inland than it is today.”

Asked whether people will take seriously a report that anticipates climate effects taking place a century or more in the future, Love said the current generation should be making plans for its descendants.

“We want to leave the planet to our children and grandchildren in ways that is hospitable to life, and this is one of the ways we can do that.”

For its part, Delaware has set a goal of reducing carbon emissions by 30 percent from 2008 levels and has already achieved 78 percent of that goal, Love said. She added that the state is part of the Regional Greenhouse Gas Initiative, a multi-state program to cut carbon emissions in the northeast.

While the study advocates tough emissions standards as a way of mitigating catastrophic sea-level rise, it argues that some flooding is inevitable.

“The best-case scenario is bad but it is a great deal better than the worst-case scenario,” said Ben Strauss, Vice President for Sea Level and Climate Impacts at Climate Central.

He said the paper has been released in the run-up to the global climate talks in Paris in December when world leaders will try to agree carbon limits that would hold the global average temperature increase to 2 degrees C.

“We have been working and hoping to get this research out ahead of the global climate talks in Paris because we believe it holds useful information for leaders to consider as they make their carbon choices and negotiate,” said Strauss.

Climate Central, which has previously produced online tools allowing users to anticipate the local effects of climate change, projected the population of hundreds of cities nationwide that would be displaced by rising sea levels after 2100 under four different carbon-emission scenarios.

The scenarios, called Representative Concentration Pathways (RCP), are given numerical values that represent policies ranging from “extreme” cuts to “unchecked pollution”. The latter projection, RCP 8.5, would eventually result in 3.3 degrees C of warming and 7.1 meters of sea-level rise (SLR), both at some point beyond the end of the 21st century. The long-term SLR projection is about seven times the consensus estimate for the global increase by 2100.

Even “extreme” carbon cuts, called RCP 2.6, would result in long-term “locked in” global sea-level rise of 2.4 meters over the long term because of historic and current carbon emissions, the study said.

Such radical cuts could consist of a rapid switch to renewable fuels and/or increased use of nuclear power, Strauss said. “It implies a massive energy transition on the scale of an industrial revolution,” he said.

The study avoided specifying when dramatic sea-level rise might occur because of uncertainties over when, or by how much, the massive Western Antarctic Ice Sheet will melt, an event that some scientists say could force global ocean levels to rise by several meters.

Michael Mann, director of the Earth System Science Center at Penn State University, said there are indications that the West Antarctic ice sheet is already “doomed” and, given additional projected global warming, that could create 12 to 14 feet of sea-level rise over time.

“Just how quickly this might happen, however – are we talking 500 years? 200 years? -- is very much uncertain,” Mann said.

He called the new paper a “useful contribution” to the literature on climate change, and said it quantifies the future impacts of sea-level rise, including under “business-as-usual policies of fossil fuel burning.”

But Mann argued that the new study might actually understate the additional flooding risk from higher sea-level rise because it does not explicitly anticipate bigger hurricanes resulting from climate change. A storm of the magnitude of Sandy, previously expected to hit only once in 3,000 years, can now be expected once a century, he said.

The paper argues that the opportunity to limit global warming to 2 degrees C “appears to be closing” but that an analysis of the costs and benefits of different carbon-control scenarios may help formulate policy.

“The results offer a new way to compare different emissions scenarios or policies and suggest that the long-term viability of hundreds of coastal municipalities and land currently inhabited by tens of millions of persons hang in the balance,” it says.

Jon has been reporting on environmental and other topics for Delaware Public Media since 2011. Stories range from sea-level rise and commercial composting to the rebuilding program at Prime Hook National Wildlife Refuge and the University of Delaware’s aborted data center plan.
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