Irma And Harvey: Very Different Storms, But Both Affected By Climate Change

Irma And Harvey: Very Different Storms, But Both Affected By Climate Change
A Texas National Guardsman carries a resident from her flooded home following Hurricane Harvey in Houston, Aug. 27, 2017

There has been no let up since Hurricane Harvey dumped record-breaking rains on the Houston area of Texas. Hurricane Irma lashed parts of the Caribbean and Cuba and devastated the Florida Keys and the state’s west coast.

We also have Hurricane Jose following Irma through the Caribbean, and Hurricane Katia, now downgraded after tracking through parts of eastern Mexico.

This very active season comes after a “hurricane drought” with very few major storms making landfall on the US coast over the previous decade.

So why are we seeing so many hurricanes now? Is climate change to blame?

How to make a hurricane

There are several vital ingredients needed for hurricanes to form. These include an initial disturbance in the atmosphere for the storm to form around, very warm sea surface temperatures to sustain the storm, and a lack of vertical wind shear so the storm is not torn apart during its formation.

In the Atlantic Ocean, hurricanes often form near Cape Verde off the coast of West Africa. They then track westward towards the Caribbean and the US.

Lots of factors can affect how strong these storms ultimately become, including how much time they spend gathering strength over the ocean, and the background weather patterns through which they travel.

This storm season we have seen sea temperatures persistently 1-2℃ above normal over the tropical Atlantic Ocean, which has allowed stronger storms to form and develop.

Atlantic sea temperatures have warmed over the past century, thus enhancing one of the key ingredients for hurricane formation. The climate change influence is clear for the sea temperatures, but not so much for the other ingredients required in forming hurricanes.

Harvey and Irma

While we have low confidence in the effect of human-caused climate change on hurricane formation, it is clear that climate change is enhancing some of the impacts of these storms.

Hurricane Harvey hit southern Texas hard by stalling over the Houston area and dumping huge amounts of rain. Climate change might have contributed to the stalling effect, but what’s clearer is that climate change is making intense extreme rainfall events like we saw over Houston more likely. By warming the atmosphere we’re also increasing its capacity to carry moisture.

When we have the trigger for heavy rainfall, climate change makes it rain harder.

Hurricane Irma is a very different beast to Harvey. It devastated several Caribbean islands including Anguilla and the Virgin Islands when it was a Category 5 system. It then struck Cuba before re-intensifying and moving north across the Florida Keys and onto the US mainland.

Irma’s main impacts have been through the storm surge, the strong winds and the heavy rains.

Climate change has likely worsened the effects of Irma. As described above, we know that climate change is intensifying extreme rain events. We also know that climate change is worsening storm surges by raising the background sea level on which these events occur.

Sea levels are projected to rise further over the coming century, by 50-100cm under a high greenhouse gas emissions scenario, and 20-50cm if we greatly reduce our emissions.

So while it’s likely that climate change is contributing to more extreme hurricanes, we have even more confidence that climate change is worsening the impacts of these storms, and will continue to do so over the coming decades.

Paving over the Gulf Coast

Besides the climate change influence, the widespread urban development on the US Gulf Coast is exacerbating the impacts of hurricanes.

Much like the Houston area, Florida also has a growing population. This means that not only are there more people in harm’s way when a major hurricane strikes, but there is also more concrete and other impervious surfaces that allow the water to pool in low-lying areas.

Is there any good news?

While climate change and development in hurricane-prone areas are worsening the impacts of these hurricanes, there are some glimmers of good news.

Scientists’ ability to track and forecast these major systems has improved greatly. Better forecasting of hurricanes allows for earlier planning for their impacts and should improve evacuation processes.

In theory, with the right plans in place, better hurricane forecasting should reduce death tolls from events like Irma. But it doesn’t necessarily reduce the economic costs of these storms, and for both Harvey and Irma the clean-up and recovery bills may be more than $100 billion each.

The ConversationIt’s clear that climate has worsened the impacts of Atlantic hurricanes and will continue to do so. Improved forecasting provides a glimmer of hope that the death tolls from future events can be reduced, even as the economic impacts increase.

About The Author

Andrew King, Climate Extremes Research Fellow, University of Melbourne

This article was originally published on The Conversation. Read the original article.

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Product Description: After major hurricanes Harvey and Irma made landfall in the United States in 2017, and as Hurricane Florence approaches the Carolinas in 2018, there have been renewed calls to do something about global warming. The popular perception that landfalling hurricanes in the U.S. are becoming more frequent or more severe, however, is shown to be incorrect. The 30 costliest hurricanes in U.S. history have indeed become more expensive in recent decades, but it is demonstrated that as damages have increased, hurricane intensity has not. The cause of increasing damages is increasing population and infrastructure in hurricane-prone areas. History has demonstrated that major hurricanes, sometimes arriving in pairs, have been part of Atlantic and Gulf coastal life for centuries. Even lake bottom sediments in Texas and Florida reveal more catastrophic hurricane landfalls 1,000 to 2,000 years ago than have happened more recently. Over the last 150 years, the number of major hurricanes hitting Texas has been the same when Gulf of Mexico water temperatures were below normal as when they were above normal. Harvey's record-setting rainfall totals were due to its slow movement, which cannot be traced to global warming (August 2017 was quite cool over most of the U.S.), combined with substantial land subsidence preventing rivers from draining more rapidly to the ocean. Major hurricane strikes in Florida since 1900 have, if anything, become somewhat less frequent and less severe. What has changed in Florida, again, is coastal development. The Miami - Fort Lauderdale metroplex now has a population of over 6 million, whereas a little over 100 years ago it was nearly zero. As a result, our vulnerability to major hurricane strikes has increased dramatically. Even with no change in hurricane activity, hurricane damages will continue to increase along with wealth and infrastructure in coastal areas. It is only a matter of time before our first trillion-dollar hurricane catastrophe occurs, and it will happen with our without carbon dioxide emissions from fossil fuel use.



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Product Description: A revealing look by someone who has loved the weather since his first memory--and has worked in the field for over 40 years--at what is really inside the man-made "climate change" agenda. The author shows through countless examples, the exploitation, politicization, and weaponization of weather and climate in an effort to promote an agenda that runs counter to the foundations this nation was built on.



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Product Description: This book provides research that shows tropical cyclones are more powerful than in the past with the most dramatic increases occurring over the North Atlantic and with the strongest hurricanes. Although such increases are correlated with warming oceans and are consistent with the thermodynamic theory of hurricane intensity, there remains doubt about the interpretation, integrity, and meaning of these results. Arising from the 5th International Summit on Hurricanes and Climate Change, this book contains new research on topics related to hurricanes and climate change. Bringing together international leading academics and researchers on various sides of the debate, the book discusses new research and expresses opinions about what is happening and what might happen in the future with regard to regional and global hurricane (tropical cyclone) activity.



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