Texas National Guardsmen assist residents affected by flooding caused by Hurricane Harvey onto a military vehicle in Houston, Aug. 27. Army National Guard / Lt. Zachary West

Michael Mann: Climate Change Worsened the Impact of Hurricane Harvey

What can we say about the role of climate change in the unprecedented disaster that is unfolding in Houston with Hurricane Harvey?

There are certain climate change-related factors that we can, with great confidence, say worsened the flooding.

Sea level rise attributable to climate change (some is due to coastal subsidence due to human disturbance e.g. oil drilling) is more than half a foot over the past few decades.

That means that the storm surge was a half foot higher than it would have been just decades ago, meaning far more flooding and destruction.

In addition to that, sea surface temperatures in the region have risen about 0.5C (close to 1F) over the past few decades, from roughly 30C (86F) to 30.5C (87F), which contributed to the very warm sea surface temperatures (30.5-31 C or 87-88F). There is a simple thermodynamic relationship known as the Clausius-Clapeyron equation that tells us there is a roughly 3 percent increase in average atmospheric moisture content for each 0.5C (~1F) of warming. Sea surface temperatures in the area where Harvey intensified were 0.5-1C warmer than current-day average temperatures, which translates to 1-1.5C warmer than the "average" temperatures a few decades ago. That means 3-5 percent more moisture in the atmosphere.

That large amount of moisture meant the potential for much greater rainfalls and greater flooding.

The combination of coastal flooding and heavy rainfall is responsible for the devastating flooding that Houston is experiencing.

Not only are the surface waters of the Gulf unusually warm right now, but there is a deep layer of warm water that Harvey was able to feed upon when it intensified at near record pace as it neared the coast. Human-caused warming is penetrating down into the ocean warming not just the surface but creating deeper layers of warm water in the Gulf and elsewhere.

So Harvey was almost certainly more intense than it would have been in the absence of human- caused warming, which means stronger winds, more wind damage and a larger storm surge (as an example of how this works, we have shown that climate change has led to a dramatic increase in storm surge risk in New York City, making devastating events like Superstorm Sandy more likely.

Finally, the more tenuous but potentially relevant climate factors: Part of what has made Harvey such a devastating storm is the way it has stalled right near the coast, continuing to pummel Houston and surrounding regions with a seemingly endless deluge which will likely top out at nearly 4 feet of rainfall over a several days-long period before it is done.

The stalling is due to very weak prevailing winds which are failing to steer the storm off to sea, allowing it to spin around and wobble back and forth like a top with no direction. This pattern, in turn, is associated with a greatly expanded subtropical high pressure system over much of the U.S. right now, with the jet stream pushed well to the north. This pattern of subtropical expansion is predicted in model simulations of human-caused climate change.

More tenuous, but possibly relevant still, is the fact that very persistent, nearly "stationary" summer weather patterns of this sort, where weather anomalies (both high pressure dry hot regions and low-pressure stormy/rainy regions) stay locked in place for many days at a time, appears to be favored by human-caused climate change. We recently published on this phenomenon:

In conclusion, while we cannot say climate change "caused" hurricane Harvey (that is an ill-posed question), we can say that it exacerbate several characteristics of the storm in a way that greatly increased the risk of damage and loss of life.

Climate change worsened the impact of Hurricane Harvey.

Show Comments ()

Those Little Produce Stickers? They’re a Big Waste Problem

By Dan Nosowitz

Those little produce stickers are ubiquitous fruits and vegetables everywhere. But, as CBC notes, they're actually a significant problem despite their small size.

Keep reading... Show less

Despite Trump’s Bluster, U.S. Officials and Scientists Maintain Climate Work with International Partners

Trump has loudly declared his intention to withdraw the U.S. from the Paris agreement, but, behind the tweets and the headlines, U.S. officials and scientists have carried on working with international partners to fight climate change, Reuters reported Wednesday.

Keep reading... Show less
Gina Loudon and administrator of the U.S. Environmental Protection Agency Scott Pruitt speaking at the 2017 Conservative Political Action Conference (CPAC) in National Harbor, Maryland. Gage Skidmore

EPA Sued Over Failure to Release Correspondence With Heartland Institute

The U.S. Environmental Protection Agency (EPA) is being sued for its "unlawful and unreasonable delay" in responding to requests for information about the agency's communications with the Heartland Institute, according to a complaint by the Southern Environmental Law Center (SELC) and the Environmental Defense Fund (EDF).

The Heartland Institute is an Illinois-based think tank that rejects the science of man-made climate change and has received funding from the Koch brothers and the fossil fuel industry.

Keep reading... Show less
Trump Watch
Aerial photo of Duke Energy Coal Ash Spill. Wake Forest University Center for Energy, Environment & Sustainability

Trump Administration Seeks to Gut Water Pollution Safeguards, Putting Communities at Risk

By Mary Anne Hitt

A Hollywood scriptwriter couldn't make this up. One day after new data revealed widespread toxic water contamination near coal ash disposal sites, U.S. Environmental Protection Agency (EPA) head Scott Pruitt announced a proposal to repeal the very 2015 EPA safeguards that had required this data to be tracked and released in the first place. Clean water is a basic human right that should never be treated as collateral damage on a corporate balance sheet, but that is exactly what is happening.

Keep reading... Show less
Impossible Foods

Impossible Burger Executive Grilled at Sustainable Foods Summit

An executive from a company selling a genetically engineered meat alternative faced tough questions at the Sustainable Foods Summit held in San Francisco at the end of January.

Keep reading... Show less
Elephant family in Kenya. Nzomo Victor / Flickr

Why Trump’s New Trophy Hunting Council Is a Disaster

By Elly Pepper

In early November—the same week the Trump administration announced its disastrous decision to allow elephant and lion trophy imports from Zimbabwe and Zambia—the administration decided to create an advisory committee, the International Wildlife Conservation Council (IWCC), to advise Trump on how to enhance trophy hunters' ability to hunt internationally.

Yup, that means the administration now has a council dedicated exclusively to promoting the killing of more imperiled species, like elephants and lions, for sport. The council's mandate includes counseling Trump on the economic, conservation, and anti-poaching benefits of trophy hunting, of which there are very few. Sadly, Trump doesn't want advice on the many drawbacks of trophy hunting.

Keep reading... Show less
A robot bee from a season three episode of Black Mirror on Netflix

Walmart Files Patent for Robot Bees

With the mass die-off of bees spelling trouble for agriculture, the world's largest retailer has filed patents for the use of "unmanned vehicles," or drones, to aid with pollination and crop production.

In U.S. Patent Office documents made public last week, Walmart has applied for six patents on drones designed to identify pest damage, spray pesticides and pollinate plants.

Keep reading... Show less
The iconic moai of Easter Island are threatened by erosion caused by rising seas. Aupaelfary / CC-BY-SA 3.0

Climate Change Threatens Easter Island

Easter Island has long served as a reminder of what happens to a civilization when the environment it depends upon collapses. Now, the iconic remains of that civilization are under threat from a new environmental challenge: global climate change.

Easter Island, Rapa Nui in Polynesian, is surrounded by statues called moai situated on top of ahu, or platforms. But according to an in-depth report for The New York Times published Thursday, the moai are now at risk from erosion caused by sea level rise.

Keep reading... Show less


The best of EcoWatch, right in your inbox. Sign up for our email newsletter!