Extreme floods that once swamped coastal communities only rarely are becoming far more c
ommon as climate change caused by humans pushes sea levels higher, according to new research published Wednesday. Experts say the findings are crucial for making plans about floods and coastal infrastructure as the planet warms.
These big coastal floods happen when high tides and storm surges — the amount above normal tide level — combine with seas that are already rising. Those pile on top of natural climate patterns and other human influence.
Climate change has strengthened storms like Hurricane Ian, which caused significant flooding in
022, scientists say. Flooding threatens hundreds of millions of people each year in low-lying coastal areas across the globe. It also causes billions of dollars in damage and can be deadly.
Floods that historically had a 1% chance of striking a coastline in a year are now about 12 times more likely, on average, according to a new study published in the journal Nature Climate Change on Wednesday. Those events hav
e become about four times more likely due to human-driven climate change, the research shows.
Researchers looked at how often extreme sea level events — which cause coastal flooding — happen by considering long-term records from tide gauges at more than 100 sites, as well as using climate modeling. The study looked
at the increase from 1900 to 2005. It was limited through 2005 becaus
e after that, there weren’t enough models that could point to instances of human-driven cli
mate change. The researchers said their findings likely understate today’s risk, because human contributions to changes in coastal extremes have only increased since then.
Researchers looked at which changes were caused by human activity, natural forces or shifts in the landscape. Although sea level changes earlier in the 20th
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century could mostly be chalked up to natural forces, the scientists found that since the 1960s, human-caused warming was the main reason sea levels are going up.
A separate study published in the journal Science Advances on Wednesday also supports the idea that extreme ocean heights come from climate change, sp
ecifically around 58% of the days with big floods from 2000 to 2018. Climate change has also, on average, nearly tripled the number of days where the sea tops extreme flood levels since the 1970s, according to that study.
“Essentially every coastal flood today has human fingerprints on it through climate change,” said Ben Strauss, chief scientist at Climate Central and a co-author of the Science Advances study. “Without the extra bit of sea level rise caused
by global heating, most of these events would not have reached the status of flood.”
The research in Nature Climate Change didn’t fully examine individual human factors, said Sönke Dangendorf, the lead author, but he noted greenhouse gases — the result of burning fossil fuels such as oil, gas and coal — are the most significant.
“Since the 1970s, it’s by far the dominating factor, and this is of course not good news,” said Dangendorf, also an associate professor at Tulane University. He said the threat is growing, and communities need to do more to prepare.
