The ‘Human Fingerprints’ On Thousands Of American Floods


The effects of man-made climate change are well and truly already upon us, reports Thom Mitchell.

New research released this week has dusted down the “human fingerprints on thousands of recent floods”, and found that sea level rise was the cause of two thirds of American floods since 1950.

The study looked at 27 tidal gauges around the United States, and found that since mid-century nearly 6,000 ‘nuisance’ floods would not have happened if not for human-induced greenhouse gas emissions.

And as sea levels rise, things are only getting worse: Since 1950, there has been an unbroken upward trend in the number of flood days caused by anthropogenic climate change, according to the report published by American think-tank Climate Central.

Between 1955 and 1965, around 45 per cent flood events were attributed to climate change. In the decade to 2014 however, a staggering 76 per cent of floods were pushed over the levee by mankind.


The study drew its conclusions by taking estimates of how much sea-level rise humans have caused, and detracting that unnatural increase from the levels reached during a given flood event.

If the National Weather Service’s threshold for a ‘nuisance flood’ wouldn’t have been crossed without sea-level rise caused by unnatural emissions, it was found to have been ‘caused’ by climate change.

The floods in question don’t neccesarily cause major damage, but the report said they “do cause material harm, inconvenience and economic drag”.

The impacts of sea level rise on particular locations varied across America, with the worst impacts identified in the Mid-Atlantic states.

Climate Central has also developed an interactive map which allows the user to explore how impacts varied across regions.

While the thousands of man-made floods may not be extreme now, they are going to get worse.

Last year was officially the hottest on record, surpassing the previous record set in 2014. Out of the last 136 years, 15 of the 16 hottest globally averaged years have occurred since the turn of the millennium.

At the moment though, Climate Central’s Benjamin Strauss said the flooding is of a scale “that closes coastal area roads, overwhelms storm drains, and compromises infrastructure”.

“It doesn’t wreck your home, but it could make it hard to get to work, or even to flush the toilet,” said Strauss, who has published widely on sea-level rise.

The three other scientists listed as authors to the report are Robert Kopp, of Rutgers University; William Sweet, of America’s National Oceanic and Atmospheric Administration; and Klaus Bittermann, of the Potsdam Institute for Climate Impacts Research.

You can read the full report here.

Thom Mitchell is New Matilda's Environment Reporter.