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September 1, 2017 at 10:08 am #73559znModerator
What do we know about the relationship between climate change and Hurricane Harvey?
Manuela Tobias
Hurricane Harvey has dumped more water on the United States than any other weather event in history, and its costs are expected to be huge.
The unprecedented storm has inevitably posed the question: What impact has climate change had on producing Hurricane Harvey? We took a look at what scientists had to say.
Keep in mind: None of the experts we talked to said climate change caused Hurricane Harvey. Instead, some posited that climate change exacerbated the effects of the storm. The degrees of exacerbation vary, though, sometimes significantly.
A draft report on climate science conducted by 13 federal agencies as part of the National Climate Assessment said models showed the number of very intense storms have been rising as a result of a warmer world. But the trend has yet to rise above normal variation.
The report also said that scientists are better able to attribute weather events to climate change than they used to be, but linking individual events to climate change is more complicated. The scientists we spoke to about Hurricane Harvey expressed a similar challenge.
Below, we’ll outline some general concepts of climate change and then address whether they influenced Hurricane Harvey.
Precipitation
In a warmer world, there’s more water vapor that storms can sweep up and dump on us.
“While it is not yet possible to determine exactly how much of the rainfall associated with Harvey was due to climate change versus how much would have occurred naturally, nearly every scientific study agrees that, as the world warms, on average the amount of rainfall associated with hurricanes will increase,” said Katharine Hayhoe, a climate scientist at Texas Tech University in Lubbock.
Heavy downpours are on the rise in the United States, according to a 2014 report by 13 federal agencies. But we found differing estimates for how climate change might have affected rainfall from Harvey.
According to Chris Landsea, science and operations officer at the National Hurricane Center, the amount of increased precipitation in Harvey is not significant. Landsea expects a 10 percent surge in rainfall by the end of the century due to climate change, which he predicts would only have only increased rainfall by an inch or two in this case.
Kevin Trenberth, a scientist at the National Center for Atmospheric Research, said he could justify a 5 to 15 percent increase in rainfall during Harvey from climate change effects, which then increase with natural variability.
“So the storm is a bit more intense, bigger and longer lasting than it otherwise would be,” Trenberth wrote to PolitiFact.
Storm surge
As Earth’s temperature warms, land-based ice melts and ocean water expands, causing sea levels to rise. This in turn increases the risks that the sea will rise with the atmospheric pressures of a storm, causing more waves and flooding.
If sea level rise continues at the current pattern, Landsea expects every single hurricane to have a 2-foot higher storm surge by the end of the century.
Trenberth attributed half a foot of the flooding in this case to climate change.
In addition to rising sea levels, the storm surge in Harvey was also tied to erosion, subsidence, saltwater intrusion and the impact of past hurricanes.
Storm intensity
Warm oceans may also increase the intensity of hurricanes. Tropical storms use the ocean to fuel their growth like a battery, so warmer temperatures make storms stronger and intensify them more quickly. Over 90 percent of the excess heat in the atmosphere caused by climate change is going to the ocean.
However, it’s not so simple to connect climate change to the intensity of Harvey, or any other hurricane for that matter. There are other atmospheric factors at play, such as changes in air temperature at the top of the hurricane, that can offset warmer ocean temperatures.
Climate science researchers want to answer this question, but they haven’t reached a verdict just yet. What some researchers have shown is that the frequency of hurricanes is decreasing, while the intensity increases. That would mean fewer storms, but the storms would be more intense with greater potential for destruction.
Some scientists attribute abnormally high Gulf of Mexico temperatures to the storm’s rapid intensification before it hit the ground, but they also can’t wholly link the temperatures to climate change. The Gulf has been ripe enough for hurricanes for three decades, but it still doesn’t produce them every year.
Stagnation
Almost every scientist we spoke with agreed that the most remarkable feature of Harvey is how long it lingered atop Houston, which was crucial in creating the staggering rain totals. But that is also the part of the storm with the least conclusive evidence linking it to climate change.
Several studies found that hurricane-steering winds have weakened and shifted northward in recent decades over North America, increasing the likelihood of slow-movers like Harvey in the future. A recent paper by Penn State professor Michael Mann showed how blocking patterns in general become more common in a warmer world.
“These studies require painstaking, detailed analyses that take years to complete so there is nothing we as scientists can say right now about the extent to which human-induced change was involved in determining Harvey’s path, or even whether it was at all,” Hayhoe said.
Kerry Emanuel, a professor of atmospheric science at Massachusetts Institute of Technology, found that steering currents had weakened significantly since 2010, but “the suddenness of the decline weighs against an explanation in terms of anthropogenic climate change.”
Preparation
Scientists may disagree on the degree to which anthropogenic (or human-caused) climate change intensified Harvey, but almost all concurred that Houston’s lack of preparation for it magnified its ramifications.
Urbanization turned prairies and forests into concrete, reducing the land’s capacity to absorb rainfall, and lax zoning codes gave way to development more prone to cave to the flooding. Paired with an explosion in the city’s population, the damages snowballed.
Many of the scientists we spoke with nonetheless stressed that in addition to infrastructure, lawmakers must focus on addressing climate change.
“We’re doing a huge disservice if we put off the reality that we are changing the climate and the sea levels if we wait until we do fancy analyses (on storms like Harvey) years later. It’s time to face up to the fact that some of these are going to become the new norm,” said Harold Wanless, chair of the geological sciences department at the University of Miami.
September 2, 2017 at 6:59 am #73592znModeratorConservative groups shrug off link between tropical storm Harvey and climate change
Myron Ebell, who headed the EPA’s transition team when Trump became president, said the last decade has been a period of ‘low hurricane activityConservative groups with close links to the Trump administration have sought to ridicule the link between climate change and events such as tropical storm Harvey, amid warnings from scientists that storms are being exacerbated by warming temperatures.
Harvey, which smashed into the Texas coast on Friday, rapidly developed into a Category 4 hurricane and has drenched parts of Houston with around 50in of rain in less than a week, more than the city typically receives in a year. So much rain fell that the National Weather Service had to add new colours to its maps.
The flooding has resulted in at least 15 deaths, with more than 30,000 people forced from their homes. Fema has warned that hundreds of thousands of people will require federal help for several years, with Greg Abbott, governor of Texas, calling Harvey “one of the largest disasters America has ever faced”. Insurers have warned the cost of the damage could amount to $100bn.
Some scientists have pointed to the tropical storm as further evidence of the dangers of climate change, with Penn State University professor of meteorology Michael Mann stating that warming temperatures “worsened the impact” of the storm, heightening the risk to life and property.
Conservative groups, however, have mobilized to downplay or mock any association between the storm and climate change. Myron Ebell, who headed the Environmental Protection Agency’s transition team when Donald Trump became president, said the last decade has been a “period of low hurricane activity” and pointed out that previous hurricanes occurred when emissions were lower.
“Instead of wasting colossal sums of money on reducing greenhouse gas emissions, much smaller amounts should be spent on improving the infrastructure that protects the Gulf and Atlantic costs,” said Ebell, who is director of environmental policy at the Competitive Enterprise Institute, a libertarian thinktank that has received donations from fossil fuel companies such as Exxon Mobil.
Thomas Pyle, who led Trump’s transition team for the department of energy, said: “It is unfortunate, but not surprising, that the left is exploiting Hurricane Harvey to try and advance their political agenda, but it won’t work.
“When everything is a problem related to climate change, the solutions no longer become attainable. That is their fundamental problem.”
Pyle is president of the Institute of Energy Research, which was founded in Houston but is now based in Washington DC. The nonprofit organization has consistently questioned the science of climate change and has close ties to the Koch family.
The Heartland Institute, a prominent conservative group that produced a blueprint of cuts to the EPA that has been mirrored by the Trump administration’s budget, quoted a procession of figures from the worlds of economics, mathematics and engineering to ridicule the climate change dimension of Harvey.
“In the bizarro world of the climate change cultists … Harvey will be creatively spun to ‘prove’ there are dire effects linked to man-created climate change, a theory that is not proven by the available science,” said Bette Grande, a Heartland research fellow and a Republican who served in the North Dakota state legislature until 2014.
“Facts do not get in the way of climate change alarmism, and we will continue to fight for the truth in the months and years to come.”
Harvey was the most powerful storm to hit Texas in 50 years, but according to the National Oceanic and Atmospheric Administration, it is “premature” to conclude that there has already been an increase in Atlantic-born hurricanes due to temperatures that have risen globally, on average, by around 1C since the industrial revolution.
Scientists have also been reluctant to assign individual storms to climate change but recent research has sought to isolate global changes from natural variability in disasters such as Hurricane Katrina, which devastated New Orleans in 2005.
However, researchers are also increasingly certain that the warming of the atmosphere and oceans is likely to fuel longer or more destructive hurricanes. A draft of the upcoming national climate assessment states there is “high confidence” that there will be an increase in the intensity and precipitation rates of hurricanes and typhoons in the Atlantic and Pacific as temperatures rise further.
Harvey may well fit that theory, according to climate scientist Kevin Trenberth, as the hurricane managed to turn from a tropical depression to a category four event in little more than two days, fed by a patch of the Gulf of Mexico that was up to 4C warmer than the long term average.
“When storms start to get going, they churn up water from deeper in the ocean and this colder water can slow them down,” said Trenberth, a senior scientist at the National Center for Atmospheric Research. “But if the upwelling water is warmer, it gives them a longer lifetime and larger intensity. There is now more ocean heat deep below the surface. The Atlantic was primed for an event like this.”
While the number of hurricanes may actually fall, scientists warn the remaining events will likely be stronger. A warmer atmosphere holds more evaporated water, which can fuel precipitation – Trenberth said as much as 30% of Harvey’s rainfall could be attributed to global warming. For lower-lying areas, the storm surge created by hurricanes is worsened by a sea level that is rising, on average, by around 3.5mm a year across the globe.
The oil and gas industry has sought to see off the threat in the Gulf of Mexico with taller platforms – post-Katrina, offshore rigs are around 90ft above sea level compared to 70ft in the 1990s – but the Houston, the epicenter of the industry, is considered vulnerable due to its relaxed approach to planning that has seen housing built in flood-prone areas.
Barack Obama’s administration established a rule that sought to flood-proof new federal infrastructure projects by demanding they incorporate the latest climate change science. Last week, Trump announced he would scrap the rule, provoking a rebuke from Carlos Curbelo, a Florida Republican congressman who called the move “irresponsible”.
Curbelo, who has attempted to rally Republicans to address climate change, wouldn’t comment on the climate change link to Harvey. Ted Cruz and John Cornyn, Texas’s Republican senators, didn’t respond to questions on the climate link, nor did Abbott, the state’s governor, or Dan Patrick, Texas’s lieutenant governor. All four of the Texas politicians have expressed doubts over the broad scientific understanding that the world is warming and that human activity is the primary cause.
“It’s essential to talk about climate change in relation to events like Hurricane Harvey and it’s sad a lot of reports don’t mention it in any way,” said Trenberth.
“You don’t want to overstate it but climate change is a contributor and is making storms more intense. A relatively small increase in intensity can do a tremendous amount of damage. It’s enough for thresholds to be crossed and for things to start breaking.”
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