Democrats kick up a storm over climate change and Dorian
Hurricane Dorian’s punishing sweep up the U.S. coast is giving Democrats an opening to hammer their message on the urgency of climate change — an issue where they hope to seize the advantage over President Donald Trump and his scoffing at mainstream science.
But at the same time, researchers express caution about how much blame to place on humans for the tropics’ destructive cyclones, though they warn that a warming planet will make the storms more intense and damaging.
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The increasing hurricane threat was a repeated theme during CNN’s seven-hour climate change town hall on Wednesday, coming just after Dorian had pulverized parts of the Bahamas and begun wheeling past Florida. Dorian, whose sustained winds reached a near-record 185 mph last weekend, is only the 35th Atlantic hurricane known to have reached Category 5 since official records began in 1851 — but also one of five to achieve that elite status in the past four years.
Democrats struck a contrast with Trump, who has dismissed man-made climate change as a Chinese hoax and has shredded the Obama-era policies designed to reduce planet-warming emissions.
Trump is also taking flack this week for presenting a doctored map of Dorian, which showed a nonexistent forecast cone threatening Alabama, and for proposing to siphon hurricane recovery money from Puerto Rico to pay for a border wall.
“The president is busy drawing with a Sharpie on a hurricane. He’s in a different reality,” Democratic presidential hopeful Pete Buttigieg said during Wednesday’s town hall. “The problem is we don’t have the luxury of debating whether this is an issue. I can’t think of anything I could ask him other than: ‘Would you please step aside and allow us to do something about this issue? You’re not ready to lead.'”
Trump’s outspoken rejection of climate science has become an outlier even among his political allies, who instead are embracing conservative warnings that the Democrats’ climate agenda means end times for cheeseburgers and plastic straws. Marc Lotter, strategic communications director for Trump’s reelection campaign, tweeted a photo of himself clutching a burger and soda Thursday morning while describing the CNN forum as a “seven-hour infomercial for @realDonaldTrump.”
Rather than blast CNN’s town hall as hooey, Trump tweeted eight “facts” about climate change and the environment, though several were incorrect, including false statements that the U.S. has “the world’s cleanest and safest air and water” and that China has “dumped the most carbon into the air.” In July, Trump hosted a White House event to tout the administration’s environmental agenda, which has largely been defined by scrapping climate rules.
But even as Democrats blamed climate change for stronger hurricanes — former Housing and Urban Development Secretary Julian Castro said they’re “happening more frequently and with greater intensity” while Sen. Bernie Sanders (I-Vt.) tweeted that Dorian “has everything to do with climate change” — scientists are still figuring out precisely how humans affect cyclones.
While research has found links between human-driven global warming and hurricane intensity, speed and rainfall, scientists are much less confident in that tie than they are with other climate-fueled maladies. The reasons are that many other factors also affect cyclone activity, and that the relatively skimpy historical data on hurricanes makes it hard to tease out long-term, observable differences between past storm activity and what we witness today.
“We struggle really to find strong evidence of human influence on hurricane activity via the past data,” said Tom Knutson, a research meteorologist with the National Oceanic and Atmospheric Administration whose work focuses on tropical cyclones and climate change.
Satellites only began observing hurricanes in the 1960s, which means the period of record for reliable data on global storm activity is hundreds to hundreds of thousands of times shorter than the data on ice cores, ocean sediments and other information used to determine climate variability. Even then, observations specific to hurricane intensity only became possible through new satellite technology in the 1980s.
Still, scientists say the politicians who have jumped to connect Dorian with climate change aren’t necessarily wrong.
The ocean drives cyclones and absorbs 93 percent of human-caused emissions, Texas Tech University climate scientist Katharine Hayhoe wrote Saturday on Twitter. That heat is fuel, intensifying storms faster and making them stronger.
Wide-ranging studies from the U.N. Intergovernmental Panel on Climate Change and the most recent National Climate Assessment, compiled by 13 U.S. federal agencies, have weighed in to assess how humans may be turbocharging hurricanes. Those studies said a greater proportion of hurricanes is expected to reach Category 4 and 5 levels in coming decades, even if the absolute number of hurricanes might decline as the world warms — but the IPCC had only “medium confidence” in that statement.
What’s more certain is that climate change indirectly makes hurricanes and typhoons more destructive, according to the IPCC. Extreme rainfall is expected to increase during hurricanes, worsening flooding. Hotter temperatures have raised sea levels by melting sea ice and thermal expansion, by which matter grows through excessive heat. The panel said warming waters are “driving more intense storms and greater rates of inundation in some regions,” which sea-level rise will compound.
Those factors probably boosted sea levels and elevated Dorian’s storm surges in the Bahamas, Knutson said. Studies showed the same was true during Hurricane Sandy, which slammed into New York and New Jersey in 2012.
But scientists said drawing conclusions from the spate of powerful hurricanes hitting the U.S. and Caribbean since 2016 — Matthew in 2016, Harvey and Maria in 2017, Florence in 2018 and now, Dorian — is too limited in scope.
“Bottom line: There is some evidence for an increase trend in GLOBAL intensity in the last ~ 30 years. But looking at 5 years is not the best way to look at trends,” Suzana Camargo, a scientist at Columbia University’s Lamont-Doherty Earth Observatory, said via email.
Knutson’s team of researchers wanted to find ways in which a warmer world might affect hurricane activity, even if they couldn’t definitely prove humans were driving those changes.
They found more cyclones are likely to intensify into Category 4 or 5 storms, even though modeling shows the total number declining. Increasing sea surface temperatures and depths of warmer waters make it harder to churn cold water to the surface that would diminish storm speeds, probably fueling stronger hurricanes, Knutson said.
Maximum global cyclone wind speeds would rise by a 5 percent average if the world warmed 2 degrees Celsius, his team found through climate modeling. That translates to even more destruction when hurricanes make landfall, as “the relationship between wind speed and loss is exponential,” according to a 2012 study by Harvard economist Richard Murnane published in the journal Geophysical Research Letters.
Some researchers are also looking into why cyclones like Harvey and Dorian appear to be hovering in one place for longer, in turn causing more wreckage and dropping more rain.
One theory suggests warmer temperatures stunt tropical circulation during the summer due to a hotter Arctic, as the diminishing temperature disparity between higher and lower latitudes have softened ocean circulations. That may mean the propeller that shuttles cyclones through the oceans is weakening, NOAA hurricane scientist James Kossin wrote in a 2018 study published in Nature. The slower-moving cyclones would then potentially generate more rainfall, worsening downpours.
But that theory is not universally accepted. Some scientists have contested the finding, and it’s an ongoing area of inquiry.
Scientists are more confident that stalled hurricanes have the potential to suffocate cities and towns with rain. Climate models show clear signals of heavier precipitation from hurricanes in a hotter world, as a warmer atmosphere can hold more moisture and also creates more vapor.
Two studies said Harvey, which pounded the Houston area with record rainfall, is a harbinger for such storms. One study said climate change boosted Harvey’s rainfall by 38 percent. The other study, published by members of the World Weather Attribution group in the journal Environmental Research Letters, concluded that human-caused warming intensified the storm’s rainfall by 15 percent and made a storm like Harvey 1.5 times more likely.