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Did global warming cause Hurricane Harvey?

A sign blows in the wind after being partially torn from its frame by winds from Hurricane Harvey on Aug. 25, 2017, in Corpus Christi. (Joe Raedle/Getty Images)

The question is going to be asked. Many times. By many people. Did global warming cause Hurricane Harvey? While there is tremendous scientific agreement among scientists about the basic science of climate change, politics and social media have created an atmosphere where a lot of incorrect information is being bantered about. Here's the truth about the relationship between global warming and Hurricane Harvey:

Scientists are uncertain about whether or not global warming will cause more hurricanes. In fact, some scientists say that a warmer planet will actually result in fewer hurricanes. However, that is not the entire story. A warming world means that ocean temperatures increase too, and we all know that warm ocean water is the fuel that powers hurricanes.

So even if the coming decades show a decrease in overall hurricanes, those hurricanes that do develop in otherwise favorable conditions will likely be stronger.

The bottom line is that our future may be one of fewer but stronger hurricanes. Is that good or bad news? Fewer hurricanes mean a lower chance that one hits the U.S. coastline. But a hurricane that does form and heads toward the U.S. will likely be stronger, with a more severe storm surge and higher winds.

Something else to consider is that, as the world warms, more ocean water evaporates into the atmosphere (which has been documented -- it's happening).This water vapor is what hurricanes turn into rainfall.

Our warmer world with higher atmospheric humidity means that tropical weather systems have more moisture to tap into, which means greater potential for increased rainfall. Statistics show that extreme precipitation events nationwide are increasing, and this also applies to tropical systems.

What most people don't realize is that, as summer wanes and we transition into fall, hurricanes are the atmosphere's natural mechanism to return the summertime water vapor back into the ocean. So hurricanes are necessary to balance the planet's water budget. The only problem is that people get in the way, and hurricanes of the future likely will have higher rainfall and increased potential for catastrophic flooding events.

So let's now apply all of this to Hurricane Harvey:

Did global warming cause Harvey? No. Harvey could have developed regardless of the warming climate. 

Could global warming have affected Harvey's strength at landfall? Harvey strengthened rapidly from a Category 1 to a Category 4 storm in just over a day, undoubtedly due to very warm Gulf of Mexico waters it traveled over. This is the first Category 4 storm to make landfall in Texas since Hurricane Carla in 1961. 

Since global warming is warming our oceans, it is possible that the warmer Gulf temperatures have been impacted by the warming climate. So global warming may have been part of the cause that Harvey rapidly intensified Friday.

Is global warming causing the incredible rain amounts expected with Harvey? As I explained above, increased atmospheric humidity due to global warming is making storms like Harvey more predisposed to heavier rainfall. However, this is not the only reason the Gulf Coast will see such extraordinary rain totals. 

Remember that most hurricanes come and go...they make landfall and keep on moving. Hurricane Harvey has become a tourist; it's going to hang around for a while and meander due to weak steering currents. 

While most people focus on wind, the true destructive power of this storm will result from water. Bands of torrential rain will plague southeast Texas into the middle of next week. Think about that for a moment:  hurricane/tropical storm induced heavy rain bands, day after day.

The bottom line is that, while global warming may have provided Harvey with extra water vapor to generate increased rainfall, the bigger reason for the catastrophic rain amounts is the storm's unusually slow movement.

By the way, there is no way to know, based upon our current knowledge, whether or not global warming has had any impact on Harvey's slow movement. Hopefully, future research will answer that question.

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