An attribution study by scientists ahead of Florence’s landfall, expected in North Carolina on Thursday, found that the storm will be about 50 miles (80km) larger in diameter than it would be if human activity had not warmed the planet.
The hurricane is expected to bring about 50% more precipitation, delivering as much as 20in (51cm) of rainfall in coastal areas, due to climate change. The forecast was completed by researchers at Stony Brook University and Lawrence Berkeley National Laboratory.
“Dangerous climate change is here, it’s not a problem for future generations,” said Michael Wehner, staff scientist at Lawrence Berkeley National Laboratory. “These risks have been permanently increased and we have to accept that fact.”
Previous attribution studies have looked at the impact of climate change on hurricanes after the storms occur, such as Hurricane Harvey, which researchers said had three times more rainfall than it would have done without global warming when it crunched into Texas last year.
But this is the first such attribution made before a storm actually reaches the shoreline. “We are now confident enough to make forecasts rather than hindcasts,” said Wehner.
Scientists were previously reluctant to link individual storms, wildfires or heatwaves to the background trend of climate change. However, the field of attribution science has advanced rapidly, to the point where researchers now feel able to ascertain a level of influence before a disaster even unfolds.
“The idea we can’t attribute individual events to climate change is out of date, it’s just no longer true,” said Wehner. “We’ve reached the point where we can say this confidently.”
Climate change fuels hurricanes by increasing the amount of moisture in the atmosphere and heightening the warmth of the oceans. Several storms that form in the Atlantic have intensified to unusual strength in recent years, as part of a trend that scientists say is consistent with a warming world.
Hurricane Florence peaked as a category four hurricane, threatening winds of 130mph, although it has since weakened slightly. It is still expected to bring a storm surge of up to 13ft (4 metres), plus waves, at the North Carolina coast on Thursday before slowing down and dumping a huge amount of rain, triggering damaging flooding further inland.
More than a million people have been told to flee coastal areas, with states of emergency declared in North and South Carolina, Virginia, Georgia, Maryland and Washington DC. The National Hurricane Center has called Florence a “storm of a lifetime”.
The tempest is expected to have a wide impact, reaching deep into North Carolina. Elvia Walkingstick, a teacher, said even her community in Cherokee, near the Tennessee border, was making preparations for the storm.
“There’s a very real possibility it could be that bad, so we will wait to see what happens,” she said. “We are bracing for climate change because we are on the front lines, we are living it.
“It’s ignorant and suicidal not to think of climate change as a reality . We’d be dumb to think it isn’t true. Ignorance isn’t an excuse any more.”