Did climate change effect hurricanes Irma and Harvey?

Meteorologist tackles global warming questions, wants to set record straight

(GMG) – The question is going to be asked many times, by many people: Did global warming cause or have any impact on Hurricane Irma? What about Harvey?

While there is tremendous 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 hurricanes Irma and Harvey.

Scientists are uncertain about whether 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 power 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 Florida. But a hurricane that does form and heads our way 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 -- also due to higher storm surges, resulting from higher sea levels from the warming climate.

Now, let's apply all of this information to hurricanes Irma and Harvey:


Did global warming cause Irma or Harvey? 

No. Both hurricanes could have developed, regardless of the warming climate. 

Could global warming have affected Irma’s record strength, or Harvey's rapid intensification, just before 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 in otherwise favorable conditions. It was the first Category 4 storm to make landfall in Texas since Hurricane Carla in 1961. Irma became the strongest Atlantic basin hurricane when its winds increased to 185 mph, also due to very warm ocean temperatures and otherwise favorable conditions. There is no question that the warmer ocean temperatures we’re experiencing now have been impacted by the warming climate. So, global warming may have been part of the reason that Harvey rapidly intensified just before landfall, and Irma became a record-breaking hurricane.

Did global warming cause the incredible rain amounts that Harvey produced?

As we discussed above, increased atmospheric humidity due to global warming is making storms such as Harvey more predisposed to heavier rainfall. However, this is not the only reason Texas saw such extraordinary rain totals.

Remember that most hurricanes (such as Irma) come and go: they make landfall and keep on moving.

Hurricane Harvey became a tourist. It hung around for a while and meandered due to weak steering currents.  While most people focus on wind, the true destructive power of that storm was water. Bands of torrential rain plagued southeast Texas for more than five straight days.

Think about that for a moment: Hurricane and 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 was the storm's unusually slow movement.  And by the way, there is no way to know, based upon our current knowledge, whether global warming had any impact on Harvey's slow movement.

Hopefully, future research will answer that question.

By Meteorologist Paul Gross

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