FacebookTwitterGoogle+RedditEmail

The Real Lesson of Katrina: the Worst is Yet to Come

Three weeks and three days before Hurricane Katrina devastated New Orleans 10 years ago, a paper of mine appeared in the scientific journal Nature.

It showed that North Atlantic hurricane power was strongly correlated with the temperature of the tropical Atlantic during hurricane season, and that both had been increasing rapidly over the previous 30 years or so. It attributed these increases to a combination of natural climate oscillations and to global warming.

Had Katrina not occurred, this paper and another by an independent team would merely have contributed to the slowly accumulating literature on the relationship between climate and hurricanes.

Instead, the two papers inspired a media firestorm, polarizing popular opinion and, to some extent, scientists themselves, on whether global warming was in some way responsible for Katrina.

While the firestorm was mostly destructive, benefiting only the media, it had a silver lining in inspiring a much more concerted effort by atmospheric and climate scientists to understand how hurricanes influence and are influenced by climate.

We have learned much in the intervening years.

 

Sea Level and Storm Surges

An obvious point is that slowly rising sea levels increase the probability of storm-induced surges even when the statistics of the storms, such as top wind speed, themselves remain stable. Storm surges are physically the same thing as tsunamis but driven by wind and atmospheric pressure rather than the shaking seafloor, and they typically arrive near the peak of the storm’s fury.

As with Katrina and Sandy, they are often the most destructive aspects of hurricanes. Had Sandy struck New York a century ago, there would have been substantially less flooding, as sea level was then roughly a foot lower. As sea level increases at an accelerating pace, we can expect more devastating coastal flooding from storms.

Potential Intensity

What about the storms themselves? Hurricanes are giant heat engines driven by the thermodynamic disequilibrium between the tropical oceans and atmosphere.

This disequilibrium drives a strong flow of heat from the ocean to the atmosphere and is a direct consequence of the greenhouse effect: the tropical atmosphere is so opaque to infrared radiation that the sea surface cannot cool very much by directly radiating heat to space. Instead, it cools mostly by the evaporation of water, the same mechanism by which our sweaty bodies cool on a hot day.

To maintain this evaporation, the sea and atmosphere must be in a state of thermodynamic disequilibrium. As we add greenhouse gases to the atmosphere, this thermodynamic disequilibrium must increase so that cooling by evaporation can compensate the loss of direct infrared cooling to space.

The theory of the hurricane heat engine places an upper limit on hurricane wind speeds. Called the ‘potential intensity’, it is directly proportional to this disequilibrium. Virtually every study that has been done, dating back to 1987, shows increasing potential intensity in most places as our climate continues to warm.

The average trend is about 10 miles per hour (mph) for every degree centigrade of tropical sea surface temperature increase, or roughly 20 mph for each doubling of atmospheric CO2 concentration.

It’s the Extra 20 MPH That Does the Damage

Twenty miles per hour might not seem like all that much, but economists and engineers tell us that damage from windstorms increases very rapidly with wind speed.

The actual situation is much more interesting than one might at first suspect. Human society is well adapted to common events. In Boston, a 50 mph wind will not do much damage because it occurs quite frequently and infrastructure is well adapted to it. But a 70 mph wind, which is far rarer, will cause quite a bit of damage.

As a loose rule of thumb, societies are well-adapted to events that occur, on average, once every generation or two. In many places this is codified in building codes, insurance contracts and other policies that are based on or insist on resistance to 100-year events; that is, events with an annual probability of 1%.

But to keep costs down, a structure engineered to survive a 100-year wind speed of 100 mph may very well fail at 110 mph.

Typhoon Haiyan is a case in point. The Philippines are regularly hammered by Category 5 typhoons, but it is rare that we hear about these because they seldom do much damage. In the region near Tacloban, the 100-year storm will have a landfalling peak wind speed of about 170 mph.

But Haiyan, probably the strongest hurricane or typhoon ever to be recorded at landfall, had wind speeds upwards of 190 mph, accompanied by a phenomenal storm surge. The difference between 170 mph and 190 mph in this case was more than 6,300 deaths and almost total devastation. This is what happens when events start to fall outside generational experience.

Theory and computer models show that the incidence of the strongest hurricanes – those that come closest to achieving their potential intensity – will increase as the climate warms, and there is some indication that this is happening. But these most destructive, high-category storms constitute only around 12% of the world’s tropical cyclones; the great majority do little damage but occur far more often.

Both theory and most models predict that, ironically, the frequency of such weaker storms should decline as the climate warms. Satellite data also show that storms are reaching their peak at higher latitudes, consistent with theories and models. This may portend reduced risk in some of the deep tropics but increased risk in middle latitudes.

In general, systematic changes in hurricane formation regions and tracks are of as much concern to us as changes in the overall statistics of storm frequency and intensity. So too is the expected large increase in hurricane rainfall, which drives hurricane freshwater flooding, the second deadliest consequence of these storms after flooding from storm surges.

So Much to Do, So little time

Global warming is occurring far too fast for effective human adaptation. The next ice age, like the last one, may very well put a mile of ice on top of New York City, but it will take so long for that to happen that most of us will not even notice our collective adaptation.

In contrast, adapting to the myriad changes expected over the next 100 years is such a horrendous prospect that otherwise intelligent people rebel against the idea even to the extent of denying the very existence of the risk.

This recalcitrance, coupled with rising sea levels, subsiding land and increased incidence of strong hurricanes, all but guarantees that New Orleans will have moved or have been abandoned by the next century.

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

More articles by:

Kerry Emanuel is Professor of Atmospheric Science at Massachusetts Institute of Technology.The Conversation

September 20, 2018
Michael Hudson
Wasting the Lehman Crisis: What Was Not Saved Was the Economy
John Pilger
Hold the Front Page, the Reporters are Missing
Kenn Orphan
The Power of Language in the Anthropocene
Paul Cox – Stan Cox
Puerto Rico’s Unnatural Disaster Rolls on Into Year Two
Rajan Menon
Yemen’s Descent Into Hell: a Saudi-American War of Terror
Russell Mokhiber
Nick Brana Says Dems Will Again Deny Sanders Presidential Nomination
Nicholas Levis
Three Lessons of Occupy Wall Street, With a Fair Dose of Memory
Steve Martinot
The Constitutionality of Homeless Encampments
Kevin Zeese - Margaret Flowers
The Aftershocks of the Economic Collapse Are Still Being Felt
Jesse Jackson
By Enforcing Climate Change Denial, Trump Puts Us All in Peril
George Wuerthner
Coyote Killing is Counter Productive
Mel Gurtov
On Dealing with China
Dean Baker
How to Reduce Corruption in Medicine: Remove the Money
September 19, 2018
Bruce E. Levine
When Bernie Sold Out His Hero, Anti-Authoritarians Paid
Lawrence Davidson
Political Fragmentation on the Homefront
George Ochenski
How’s That “Chinese Hoax” Treating You, Mr. President?
Cesar Chelala
The Afghan Morass
Chris Wright
Three Cheers for the Decline of the Middle Class
Howard Lisnoff
The Beat Goes On Against Protest in Saudi Arabia
Nomi Prins 
The Donald in Wonderland: Down the Financial Rabbit Hole With Trump
Jack Rasmus
On the 10th Anniversary of Lehman Brothers 2008: Can ‘IT’ Happen Again?
Richard Schuberth
Make Them Suffer Too
Geoff Beckman
Kavanaugh in Extremis
Jonathan Engel
Rather Than Mining in Irreplaceable Wilderness, Why Can’t We Mine Landfills?
Binoy Kampmark
Needled Strawberries: Food Terrorism Down Under
Michael McCaffrey
A Curious Case of Mysterious Attacks, Microwave Weapons and Media Manipulation
Elliot Sperber
Eating the Constitution
September 18, 2018
Conn Hallinan
Britain: the Anti-Semitism Debate
Tamara Pearson
Why Mexico’s Next President is No Friend of Migrants
Richard Moser
Both the Commune and Revolution
Nick Pemberton
Serena 15, Tennis Love
Binoy Kampmark
Inconvenient Realities: Climate Change and the South Pacific
Martin Billheimer
La Grand’Route: Waiting for the Bus
John Kendall Hawkins
Seymour Hersh: a Life of Adversarial Democracy at Work
Faisal Khan
Is Israel a Democracy?
John Feffer
The GOP Wants Trumpism…Without Trump
Kim Ives
The Roots of Haiti’s Movement for PetroCaribe Transparency
Dave Lindorff
We Already Have a Fake Billionaire President; Why Would We want a Real One Running in 2020?
Gerry Brown
Is China Springing Debt Traps or Throwing a Lifeline to Countries in Distress?
Pete Tucker
The Washington Post Really Wants to Stop Ben Jealous
Dean Baker
Getting It Wrong Again: Consumer Spending and the Great Recession
September 17, 2018
Melvin Goodman
What is to be Done?
Rob Urie
American Fascism
Patrick Cockburn
The Adults in the White House Trying to Save the US From Trump Are Just as Dangerous as He Is
Jeffrey St. Clair - Alexander Cockburn
The Long Fall of Bob Woodward: From Nixon’s Nemesis to Cheney’s Savior
FacebookTwitterGoogle+RedditEmail