US sea level to rise as much in next 30 years as in past century – study

Seas rising faster around the US than global average will cause ‘dramatic increase’ in number of people vulnerable to flooding

America’s vast coastline is being assailed by rapidly encroaching oceans, with up to 1ft of sea level rise expected in the next 30 years – an increase that equals the total rise seen over the past century, a major US federal government report has found.

The seas are rising significantly faster around the US than the global average, a situation that will cause a “dramatic increase” in the number of Americans, already numbering tens of millions, vulnerable to disastrous flooding, the analysis warns.

The trend, driven by the human-caused climate change, is stark – instances of “moderate” flooding at high tide, capable of damaging homes and businesses, have already increased by 50% across the US since the 1990s. This flooding is expected to become 10 times more common by 2050, on average, while major, potentially catastrophic floods are set to happen five times more often by this time.

This “profound shift” in coastal inundation means that the sort of flooding an area could expect once every two to five years is set to hit multiple times in a single year in some places, even in the absence of storms or heavy rainfall, according to the study, which was jointly authored by Nasa, the National Oceanic and Atmospheric Administration (Noaa) and six other US government agencies.

“Sea levels are continuing to rise at an alarming rate, endangering communities around the world,” said Bill Nelson, administrator of Nasa. “Science is indisputable and urgent action is required to mitigate a climate crisis that is well under way.” Rick Spinrad, administrator of Noaa, said the report should act as a “wake-up call” to the perils of the climate crisis.

The seawater lapping at the edges of the contiguous US has already risen by about a foot since 1920, a faster increase than the 6-8in (15-20cm) experienced, on average, around the world over the same period.

This sea level rise is on track to double within just 30 years around the US, although the rates of change will vary significantly across different regions. While the US west coast is expected to get 4-8in of extra sea level by 2050, the east coast will get up to 14in of raised seas and the communities ringing the Gulf of Mexico will be hit by a severe increase of up to 18in.

The uneven rate of sea level rise will influence flood risk – the western part of the Gulf coast will see 10 times as many moderate flooding events a year compared with now, for example, while the risk of such flooding will edge up only slightly in Alaska and Hawaii.

Certain communities will feel the brunt of this increasing flooding, with risks exacerbated by substandard housing, poor flood defenses and a shift in population that is seeing more people move into low-lying areas, such as Florida, that are vulnerable to the rising seas. There will be a 40% increase in flood risk in areas where at least 20% of the population is black, according to a recent study.

The seas are rising globally due to the burning of fossil fuels, which releases greenhouse gases that help heat the atmosphere and oceans. As glaciers melt away under soaring temperatures – the huge ice sheets of Greenland and Antarctica have lost more than 6tn tons of ice since the 1990s – the meltwater causes the oceans to creep upwards. The seawater itself is expanding, too, as it heats up.

The US government scientists said an improved understanding of ocean dynamics means there is confidence that the US should expect around 1ft of sea level rise over the next 30 years, with a total of 2ft expected by 2100, due to emissions already released.

But much will depend on how quickly the US, and the world, is able to slash emissions and avoid disastrous climate change, with the risk of sea level rising by up to 4ft becoming far more likely if global temperatures are allowed to escalate to 3C, or more, beyond the pre-industrial era. The world has already heated up by about 1.2C since the advent of heavy industry.

Joe Biden’s administration said the report underlined the need to slash planet-heating emissions, although the president has seen his climate agenda stall in Congress, his green reputation damaged by the continued issuing of oil and gas drilling permits, and he is now facing a looming supreme court case that may severely limit his ability to use his powers to curb pollution.

“This new data on sea rise is the latest reconfirmation that our climate crisis – as the president has said – is blinking ‘code red’,” said Gina McCarthy, Biden’s top climate adviser.

“We must redouble our efforts to cut the greenhouse gases that cause climate change while, at the same time, help our coastal communities become more resilient in the face of rising seas.”

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