Global warming alone did not
cause two of recorded history’s most intense Atlantic hurricanes—Katrina
and Rita—in 2005. Nothing is “caused” by one factor
alone, and no weather disaster in our time is entirely natural,
given humankind’s enormous “footprint” on the planet.
New Orleans will recover, we are told. A proportion of its people
surely will return. The hard truth, however, is that in a time when
the land under the city is sinking and the Gulf of Mexico is slowly
rising, as hurricanes intensify over warmer water, an ambitious
plan to rebuild New Orleans on its present site at enormous cost
may be urban suicide.
The rest of the Gulf of Mexico will recover as well, to be ready
for the next dose of a new environmental reality. Galveston has
done it before: in 1900, a Category 4 hurricane forced a storm surge
across the same island, killing 6,000 to 12,000 people who had not
been warned. Hurricanes are not new, of course. Skeptics of global
warming will remind us of this evident fact. What is new is the
frequency of intense storms, as well as the weakness of natural
defenses, such as barrier islands, along the coastlines.
New Orleans is our time’s first truly mass casualty of climate
change in the United States, killing more than 1,000 people and
creating environmental refugees in the hundreds of thousands. We
should learn from this disaster. It will not be the last.
Why, in a centuries-old city, has a hurricane caused such death
and chaos this year? New Orleans and the rest of the central Gulf
of Mexico coast have experienced many hurricanes, some of them very
severe, including Betsy in 1965 and Camille in 1969. Reasons are
many, and global warming is only part of New Orleans’ urban
Global warming is an important factor, however. As ice melts around
the world, sea levels are slowly rising. Warmer water also expands
and occupies more space. In addition, hurricanes are heat engines.
They live and die according to the warmth of the water over which
they move. One important reason why Katrina blew up so quickly into
the second most intense hurricane in U.S. history was the temperature
of the Gulf of Mexico, 88 to 90 degrees Fahrenheit.
Water temperatures vary for reasons other than global warming. Atlantic
hurricanes intensify in 20 to 30 year cycles, following changes
in water temperature. We are presently in the active phase of such
a cycle, compounded by generally rising air temperatures. Thus,
the number and intensity of hurricanes over Florida and the Gulf
Coast states has been unusually high during the past several years.
In addition to cycles in hurricane activity and warming temperatures,
the coastline marshes of the Mississippi Delta that once afforded
New Orleans and neighboring areas some protection have been subsiding
for decades, mainly because water and oil have been pumped out of
the ground, but also because the oil industry has laced the area
with transportation canals. Each hurricane’s landfall accelerates
the advance of the ocean.
The combined effects of sea-level rise and land subsidence along
the Louisiana coast have been grist for many warnings over the past
several years. Many scientific studies have asserted that sea levels
may rise between 8 and 20 inches during the 21st century. Adding
sea-level rise to ground subsidence, coastal residents in this area
can expect a net sea-level rise of 15 to 44 inches during the next
If nature was a novelist, the compounding ironies of the weather
wars couldn’t get any sharper. A large proportion of U.S. oil-refining
capacity has been built in and between New Orleans and Houston,
the areas hardest hit by Katrina and Rita. This area lives by oil
and—given the unfolding nature of rising seas and subsiding
land—may die by it. In the meantime, the government is run
by oil-related interests unable to see into a viable energy future.
Bush and his “base” stand to gain from expensive oil,
even as most other people lose. In the longer run, on the far horizon
of history (in that land about which Bush does not care “because
I’ll be dead then”) he—and we—will be in the
same position as people who bought stock in blacksmitheries 125
years ago, at the dawn of the fossil fuel age. Oil as a source of
energy has become environmentally obsolete. It is a threat to our
national security in a most fundamental sense.
In addition to national security concerns, by burning oil and other
fossil fuels we are raising the level of carbon dioxide in the atmosphere
to levels not seen since the days of the dinosaurs. Year upon year,
accelerating feedbacks in the atmosphere (such as gasification of
carbon and methane from melting permafrost in the rapidly warming
Arctic) will be more obvious than today. Additionally, the atmosphere
takes about 50 years to express fossil-fuel combustion in any given
period. Thus, today’s temperatures reflect consumption in,
roughly, 1960. Since then, world fossil-fuel consumption has increased
about 500 percent.
Thus, if we think the weather is rough now, wait 50 years. As the
atmosphere warms, storms generally become more explosive. Warmer
air holds more water vapor and allows for more intense storm development.
This has been true for tornadoes as well as hurricanes. About 110
miles southwest of Omaha, for example, the largest tornado on record
(two miles across) wiped the town of Hallam off the map during May
2004. The same area also now owns bragging rights to the largest
recorded hail, between the size of a softball and a cantaloupe.
Hurricanes and Global Warming
The relationship (or lack
thereof) between hurricane intensity and warming atmospheric temperatures
is complicated by the fact that water temperatures (like air temperatures)
sometimes vary, over periods of several decades, along with the
long-term trend “signal” provoked by greenhouse-gas levels.
For example, water temperatures in the Atlantic Ocean, which produces
nearly all the hurricanes that have an impact on the United States,
have been rising steadily since the 1970s, paralleling a general
global rise in air temperatures.
Frequency and intensity of hurricanes (as well as the number hitting
U.S. coastlines and inflicting major damage) also have been rising
during the same period. Any study that takes the record back to
the 1970s indicates a very tight relationship between ocean warming,
hurricane intensity, and air temperatures. However, during the 1950s
and 1960s, air temperatures were generally cooler than during the
1970s, but water temperatures and hurricane intensity were higher—
again, on average. By 2005 this divergence was fueling a testy debate
between some hurricane experts regarding whether, and to what degree,
hurricane intensity and frequency was related to the overall warming
trend. This debate often spilled over into the public realm as Florida
and surrounding areas were smacked by four major hurricanes in 2004
and as the 2005 hurricane season set records for the number of named
storms in July.
A study published in Nature, August 4, 2005, indicated that
the “dissipation of power” of Atlantic hurricanes had
more than doubled in the previous 30 years, with a dramatic spike
since 1995, with global warming and other variations in ocean temperatures
working together. The study, by Massachusetts Institute of Technology
climate scientist Kerry Emanuel, was the first to indicate a statistical
relationship between rising sea-surface temperatures and storm intensity.
The trend reflects longer storm lifetimes and greater intensities,
both of which Emanuel associates with increasing sea-surface temperatures.
“The large upswing in the last decade is unprecedented and
probably reflects the effect of global warming. My results suggest
that future warming may lead to an upward trend in tropical cyclone
destructive potential and—taking into account an increasing
coastal population—a substantial increase in hurricane-related
losses in the 21st century,” Emanuel wrote.
During the summer of 2004, Florida and adjacent areas were hit by
four major hurricanes (Charley, Frances, Ivan, and Jeanne) within
six weeks, as speculation mounted regarding the storms’ possible
relationship with global warming. Each of these hurricanes ranked
in the top ten such storms to hit the United States in terms of
insurance losses, until they were surpassed by Katrina and Rita.
study reached similar conclusions. By the 2080s warmer seas could
cause an average hurricane to intensify about an extra half step
on the Saffir- Simpson scale, according to a study conducted on
supercomputers at the Commerce Department’s Geophysical Fluid
Dynamics Laboratory in Princeton, New Jersey. The same study anticipates
that rainfall up to 60 miles from a hurricane’s core could
be nearly 20 percent heavier. This study is significant because
it used half a dozen computer simulations of global climate devised
by separate groups at institutions around the world.
Thomas R. Knutson and Robert E. Tuleya’s models indicate that,
assuming sea-surface temperature increases of 0.8 to 2.4 degrees
Celsius, hurricanes could become 14 percent more intense (based
on central pressure), with a 6 percent increase in maximum wind
speeds and an 18 percent rise in average precipitation rates within
100 kilometers of storm centers.
During late August 2005, Hurricane Katrina tested the emergency
preparation modeling for New Orleans and the rest of the Central
Gulf coast with 150 mile-an-hour winds, a storm surge as high as
30 feet, and the second-lowest barometric-pressure reading in U.S.
By August 30, two days after Katrina came ashore over Gulfport,
Mississippi, the Federal Emergency Management Agency (FEMA) was
calling its landfall the most significant natural disaster in the
history of the United States—80 percent of New Orleans was
under water and the city had no power, no drinking water, and no
place to bury the uncounted dead. Along the Gulf Coast, in and near
Biloxi, Gulfport, and Mobile, a 30-foot storm surge turned entire
beachfront towns into piles of broken bricks and kindling. The fetid,
humid heat was turning what remained into a stinking health hazard.
The storm surge wiped away the town of Waveland, Mississippi, 50
miles northeast of New Orleans. Large parts of Biloxi, Gulfport,
and other coastal cities and towns suffered damage on an apocalyptic
scale. Five million people lost power, many of them for several
weeks. The “worst-case scenarios” paled beside reality.
It’s Becoming Apocalyptic
Tim Wagner, Nebraska State
Insurance commissioner, in an interview in the Omaha World-Herald
three days after Katrina hit, said that global warming is causing
weather- related disasters to be more severe and more frequent.
“It’s scary,” he said. “It’s becoming apocalyptic.”
On Saturday, September 3, the sixth day after the storm’s landfall,
the Associated Press reported: “By mid-afternoon, only pockets
of stragglers remained in the streets around the convention center,
and New Orleans paramedics began carting away the dead. A once-vibrant
city of 480,000 people, overtaken just days ago by floods, looting,
rape and arson, was now an empty sodden tomb.” The New York
Times reported: “Seven days after Hurricane Katrina devastated
the Gulf Coast, the New Orleans known as America’s vibrant
capital of jazz and gala Mardi Gras celebrations was gone. In its
place was a partly submerged city of abandoned homes and ruined
businesses, of bodies in attics or floating in deserted streets,
of misery that had driven most of its nearly 500,000 residents into
a diaspora of biblical proportions…. Officials warned of an
impossible future in a destroyed city without food, water, power
or other necessities, only the specter of cholera, typhoid or mosquitoes
carrying malaria or the West Nile virus.”
before had a large city in the United States been emptied of its
people. Two weeks passed between the storm and a concerted effort
to collect bodies languishing in the gradually declining floodwaters.
The city was pumped dry in less than a month, only to witness new
flooding from a brush with Hurricane Rita, when its center came
ashore almost 300 miles southwest. The levees had become so fragile
that little more than a hard rain (not unusual in New Orleans, even
without a hurricane) could swamp many neighborhoods.
Years before, scientists in the area had modeled the same situation
in an exercise they called “Hurricane Pam.” They had known
that New Orleans would flood with massive loss of life, but the
gruesome nature of the reality had escaped even them.
Two and a half weeks after Katrina struck, President George W. Bush
stood in the French Quarter and told a national television audience
that his government, which had been severely criticized for its
tardy response to the storm, would “do what it takes”
to rebuild New Orleans and the rest of the devastated Gulf Coast.
Estimates of the cost at the time ranged up to $200 billion.
The next day, in Science, another study linked rising water
temperatures directly to the number, duration, and intensity of
hurricanes. The researchers, led by Peter J. Webster of the Georgia
Institute of Technology, found that the number of storms in the
two most powerful categories, 4 and 5, had risen to an average of
18 a year worldwide since 1990, up from 11 in the 1970s. There was
no increase in the number of storms, the researchers said, just
in their intensity. The rise in intensity coincided with an increase
of nearly 1 degree Fahrenheit in the surfaces of tropical seas around
The United States has fallen behind much of the rest of the world
in realizing that our energy paradigm must change during this century.
Even today, most families in Denmark have a share in a wind turbine.
The European Union taxes any gasoline engine larger than two
liters very heavily. Wind and solar energy are serious business
in Europe. Will the United States refuse to recognize environmental
realities? If we do, we will be emulating the people of Easter Island,
who built a high culture on a wood-based economy and (as described
by Jared Diamond in his recent book Collapse) consumed their
island’s every last tree. We owe future generations better
E. Johansen, professor of communication at the University of Nebraska
at Omaha, is author of Global Warming in the
21st Century (Praeger, 2006).