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Did Climate Change Intensify Harvey? Yes- amplifying worst effects

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Robinson Meyer  read full article in The Atlantic

Every so often, the worst-case scenario comes to pass.  As of Sunday afternoon, the remnants of Hurricane Harvey seem likely to exceed the worst forecasts that preceded the storm. The entire Houston metropolitan region is flooding: Interstates are under feet of water, local authorities have asked boat owners to join rescue efforts, and most of the streams and rivers near the city are in flood stage….“Local rainfall amounts of 50 inches would exceed any previous Texas rainfall record. The breadth and intensity of this rainfall are beyond anything experienced before,” said a statement from the National Weather Service. “Catastrophic flooding is now underway and expected to continue for several days. ”…
This means that thousands of people—and perhaps tens of thousands of people—are facing a terrifying and all-too-real struggle to survive right now. In an age when the climate is changing rapidly, a natural question to ask is: What role did human-caused global warming play in strengthening this storm?Climate scientists, who specialize in thinking about the Earth system as a whole, are often reticent to link any one weather event to global climate change. But they say that aspects of the case of Hurricane Harvey—and the recent history of tropical cyclones worldwide—suggest global warming is making a bad situation worse.…Climate change is caused by the release of greenhouse gases like carbon dioxide and methane into the atmosphere. These gases prevent some of the sun’s rays from bouncing back into space, trapping heat in the planetary system and raising air temperatures all over the world….

Storms like Harvey are helped by one of the consequences of climate change: As the air warms, some of that heat is absorbed by the ocean, which in turn raises the temperature of the sea’s upper layers.
Harvey benefitted from unusually toasty waters in the Gulf of Mexico. As the storm roared toward Houston last week, sea-surface waters near Texas rose to between 2.7 and 7.2 degrees Fahrenheit above average. These waters were some of the hottest spots of ocean surface in the world. The tropical storm, feeding off this unusual warmth, was able to progress from a tropical depression to a category-four hurricane in roughly 48 hours.“This is the main fuel for the storm,” says Kevin Trenberth, a senior scientist at the U.S. National Center for Atmospheric Research. “Although these storms occur naturally, the storm is apt to be more intense, maybe a bit bigger, longer-lasting, and with much heavier rainfalls [because of that ocean heat].”……the hurricane churned up water 100 or even 200 meters below the surface, said Trenberth, but this water was still warm—meaning that the storm could keep growing and strengthening. “Harvey was not in a good position to intensify the way it did, because it was so close to land. It’s amazing it was able to do that,” he told me…

…Trenberth says that the extra heat could make the storm more costly and more powerful, overpowering and eventually breaking local drainage systems.

The human contribution can be up to 30 percent or so up to the total rainfall coming out of the storm,” he said. “It may have been a strong storm, and it may have caused a lot of problems anyway—but [human-caused climate change] amplifies the damage considerably.”…

  • How Harvey went from a little-noticed storm to a behemoth

By Sandhya Somashekhar August 27 at 6:06 PM read full Washington Post article

Even if Harvey had been a milder storm, spinning lazily across the Gulf of Mexico, there would have been reasons for alarm early last week. For starters, the jet stream — the air current that meanders across the continent, pushing storms along a familiar path — flowed far north of Texas, and thus when Harvey crashed into the state there was nothing in the atmosphere to shove it somewhere else. Harvey stalled.

…Harvey also proved that the Gulf of Mexico — in late August, in a warming climate — can prove explosive for the development of what is generically called a tropical cyclone. In barely more than a day the storm went from a disorganized tropical depression to a significant hurricane and then all the way up to Category 4 — the second-highest rating on the Saffir-Simpson hurricane intensity scale, which is based on wind speed.

The result: a record-setting storm that within 24 hours plunged much of the nation’s fourth-largest city and its surroundings under feet of choppy brown water. It threatens to submerge even more of the region during the next few days.

“There are a lot of worst-case-scenario stars that aligned,” said Marshall Shepherd, a professor of atmospheric sciences at the University of Georgia and a past president of the American Meteorological Society. “As bad as it is now, we still have days of this to go.”

….A stunning amount of rain has fallen over Texas so far, and it is expected to continue for several more days as the storm creeps along, weakening slightly. In general, things will probably get worse before they get better; some areas might see as many as 50 inches of rainfall when all is said and done, wreaking damage that experts predict could lead to years of recovery across the region.

As of Sunday afternoon, the storm had deposited 9 trillion gallons over Southeast Texas, as bands of rain picked up moisture from the Gulf. That’s enough water to fill up the Great Salt Lake twice over, meteorology student Matthew Cappucci wrote for The Washington Post….

Experts say the lack of “steering currents” to move the storm along is unusual and probably responsible for the scale of the flooding. As of Sunday evening, the center of the storm was virtually parked at a spot about 25 miles northwest of the coastal town of Victoria — crawling southeast at 2 miles per hour toward the Gulf.

With a more common tropical storm, the damage in any one place would be mitigated by the fact that the storms move quickly, spreading the rain over a larger area.

Perhaps making things worse is something called the “brown ocean effect,” which hypothesizes that storms, which typically get their energy over the ocean or another large body of water, can absorb that energy and moisture from rain-soaked land. “The land, in effect, mimics the energy supply of the ocean,” University of Maryland Baltimore County professor Jeff Halverson wrote for the Capital Weather Gang….

Related: What you can and can’t say about climate change and Hurricane Harvey

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