About humanity’s role in worsening the catastrophe, the scientists left little doubt: “While hurricanes occur naturally, human-caused climate change is supercharging them and exacerbating the risk of major damage.”
Noting that 2017 saw three enormous hurricanes, Harvey, Irma and Maria, they focused on Harvey and the intense flooding it caused in Houston. Before Harvey came through, the oceans were the hottest on record. This heat kept the hurricane going — and more. The scientists found that, when Harvey traversed the Gulf of Mexico, it soaked up ocean heat via evaporation, packing more moisture into the atmosphere. Harvey then dumped record amounts of rain on Houston, flooding large swaths of the city. “Record high ocean heat values not only increased the fuel available to sustain and intensify Harvey, but also increased its flooding rains on land,” the researchers found. “Harvey could not have produced so much rain without human-induced climate change.”
Harvey was only a single event. But it was a spectacular one, and a useful case because the researchers could study its before-and-after effects reasonably isolated from other environmental influences.
It is still a matter of debate whether climate change will increase the number of hurricanes, but it is more and more clear that human-caused heating of the planet will boost their severity. “There will be a warmer and wetter world over oceans, and more energy available for evaporation,” the researchers wrote. Nearly all of the extra heat trapped by the greenhouse gases that humans have produced goes into the oceans. More heat in the oceans means more water vapor and, therefore, heavier rain and more flooding.
Humanity’s response must start with heading off as much unnecessary warming as possible by cutting dependence on fuels that emit heat-trapping greenhouse-gas emissions. But Harveys are already happening, so local, state and national governments also must make better preparations for the extreme weather to come. “Houston has been beset with three 500-year floods in 3 years prior to Harvey, and Miami regularly experiences ‘sunny day’ flooding with high tides,” the researchers wrote. “Why was there reportedly only 1 in 6 with flood insurance in the Houston area and Florida? Why have various flood mitigation measures not been enacted?” The scientists recommend building more levees, seawalls and flood control infrastructure, as well as adopting strong building codes, ensuring that flood insurance rates match the risk and refraining from building in dangerous areas. Houston failed to make such investments.
State and local governments can — and should — do much of this on their own. But until the country has a president who accepts scientific facts, the nation’s response will be scarily inadequate.