By the time
the rain stops, Harvey will have dumped about 1 million gallons of water for
every man, woman and child in southeastern Texas — a soggy,
record-breaking glimpse of the wet and wild future global warming could bring,
scientists say.
While scientists are quick to say climate change didn't
cause Harvey and that they haven't determined yet whether the storm was made
worse by global warming, they do note that warmer air and water mean wetter and
possibly more intense hurricanes in the future.
"This is the kind of thing we are going to get more of,"
said Princeton University climate scientist Michael Oppenheimer. "This
storm should serve as warning."
There's a scientifically accepted method for determining if some
wild weather event
has the fingerprints of man-made climate change, and it involves intricate
calculations. Those could take weeks or months to complete, and then even
longer to pass peer review.
In general, though, climate scientists agree that future storms
will dump much more rain than the same size storms did in the past.
That's because warmer air holds more water. With every degree
Fahrenheit, the atmosphere can hold and then dump an additional 4 percent of
water (7 percent for every degree Celsius), several scientists say.
Global warming also means warmer seas, and warm water is what
fuels hurricanes.
When Harvey moved toward Texas, water in the Gulf of Mexico was
nearly 2 degrees (1 degree Celsius) warmer than normal, said Weather
Underground meteorology director Jeff Masters. Hurricanes need at least 79
degrees F (26 C) as fuel, and water at least that warm ran more than 300 feet
(100 meters) deep in the Gulf, according to University of Miami hurricane
researcher Brian McNoldy.
Several studies show that the top 1 percent of the strongest
downpours are already happening much more frequently. Also, calculations done
Monday by MIT meteorology professor Kerry Emanuel show that the drenching
received by Rockport, Texas, used to be maybe a once-in-1,800-years event for that
city, but with warmer air holding more water and changes in storm steering
currents since 2010, it is now a once-every-300-years event.
There's a lot of debate among climate scientists over what role,
if any, global warming may have played in causing Harvey to stall over Texas,
which was a huge factor in the catastrophic flooding. If the hurricane had
moved on like a normal storm, it wouldn't have dumped as much rain in any one
spot.
Harvey stalled because it is sandwiched between two high-pressure
fronts that push it in opposite directions, and those fronts are stuck.
Oppenheimer and some others theorize that there's a connection
between melting sea ice in the Arctic and changes in the jet stream and the
weather patterns that make these "blocking fronts" more common.
Others, like Masters, contend it's too early to say.
University of Washington atmospheric scientist Cliff Mass said
climate change is simply not powerful enough to create off-the-chart events
like Harvey's rainfall.
"You really can't pin global warming on something this
extreme. It has to be natural variability," Mass said. "It may juice
it up slightly but not create this phenomenal anomaly."
"We're breaking one record after another with this
thing," Mass said.
Sometime Tuesday or early Wednesday, parts of the Houston region
will have broken the nearly 40-year-old U.S. record for the heaviest rainfall
from a tropical system — 48 inches (120 centimeters), set by Tropical Storm
Amelia in 1978 in Texas, several meteorologists say.
Already 15 (-9.44 Celsius)trillion gallons of rain have fallen on
a large area, and an additional 5 trillion or 6 trillion gallons are forecast
by the end of Wednesday, meteorologist Ryan Maue of WeatherBell Analytics
calculates. That's enough water to fill all the NFL and Division 1 college
football stadiums more than 100 times over.
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