Climate scientists looking to assign blame for Hurricane Harvey say that climate change is not likely to be a direct cause of the unprecedented storm.
But global warming has undoubtedly played a role in the storm and its historic precipitation, since warmer seas fuel higher-volume storms, scientists say.
“Harvey was almost certainly intense than it would have been in the absence of human-caused warming, which means stronger winds, wind damage and a larger storm surge,” Michael Mann, an atmospheric scientist at Penn State University, wrote in the Guardian on Monday.
Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research who has extensively studied the link between warming oceans — caused in large part by human activity through greenhouse gases — and extreme weather, said researchers generally don’t try to answer whether a particular event was caused by climate change.
“Is climate change contributing to the intensity, and especially the magnitude of the precipitation? Yes,” he said.
In the days leading up to Harvey’s landfall near Houston, scientists and climate activists quickly started to ask whether there was a link between human-induced climate change and the Category 4 storm.
The attribution question has been at the forefront of numerous major weather events in recent years, including California’s drought, Hurricane Sandy and the 2013 polar vortex.
But it’s taken on a new meaning in the wake of Hurricane Harvey, thanks in large part to President Trump’s doubts about climate change science and his historic efforts to roll back nearly every Obama administration policy meant to combat global warming.
Most recently, Trump signed an executive order to stop Obama’s initiative that called for federally funded infrastructure to be built to withstand the expected effects of climate change, including frequent floods.
While Trump’s policy changes are too recent for their effects be seen in the response to Harvey, some climate activists see the storm as a reminder of the effects of not taking the strong action they want against global warming.
“Once the storm has passed, the Trump administration must rethink its dangerous denial of how climate change is increasing threats to people along America’s shorelines,” said Kassie Siegel, directly of the climate law institute at the Center for Biological Diversity.
“Harvey’s destruction shows the danger of Trump’s recent order to disregard flood risks to federal infrastructure along our coasts. As climate change drives up damage from flooding and storm surges, the president is blocking efforts to protect bridges and highways from future hurricanes.”
Barry Rabe, an environmental policy professor at the University of Michigan’s Ford School of Public Policy, said past extreme weather events have not moved the needle much on the public’s perception of climate change.
“People are extremely confident, increasingly so, one way or the other on this. And it’s not clear that past singular weather disasters have had an enduring effect,” Rabe said, citing polling data from past disasters.
Harvey’s unprecedented power, rainfall and impact could buck the trend, Rabe said.
“With something this scale and magnitude, nationally or internationally significant, hitting a major urban area … it may change the thought or perception in some way.”
But not all scientists are ready to make any connection between Harvey and climate change.
Joe Bastardi, a meteorologist at WeatherBell Analytics and an outspoken climate skeptic, said Harvey is within what he would expect, given recent weather patterns.
“I could give you 100 examples of how Harvey has occurred all over the world in other places,” he said.
Bastardi believes that the climate is changing, but human activity is not the main cause.
He said Harvey is only the seventh strongest hurricane on record to hit the Texas coast on record, though the stalling over Texas, which drives up rainfall totals, has not happened before.
“While this stalling and heavy rain is unprecedented in the Houston area, you have hundreds of places across the globe where tropical cyclones have stalled,” he said.