Causes of the current heat wave are complex. Drought, high pressure and sprawl all play roles.
By Robert Lee Hotz and Erin Cline, Times Staff Writers
The heat was unreal — so blistering that a windowsill thermometer
overlooking Olympic Boulevard in downtown Los Angeles blew its top when
the mercury hit 130 degrees. People consumed so much water that parts
of the city briefly ran dry. Four people died. Dozens were hospitalized.
It was still 89 degrees at 1 a.m.
The record hot spell did not occur in 2006, but 1955, long before
scientists raised the prospect of global warming and climate change.
The extreme temperatures of this year's heat wave have been so intense
that they have created a sense of fundamental change — that somehow Los
Angeles is on the verge of a searing future.
But few events occur with such regularity or are so quickly forgotten
as Southland heat waves, with extremes of temperature rising and
falling in a regular rhythm like rolling curls of surf.
Climate experts at the Jet Propulsion Laboratory in La Cañada
Flintridge and the Scripps Institution of Oceanography in La Jolla
cautioned Tuesday that no single event — no matter how unusual — could
be directly attributed to global warming and the effects of pollution.
There is such natural variability in temperature that even a record
scorcher is just one data point in a long temperature timeline.
"To call it global warming would be overdoing it," said climatologist
Daniel R. Cayan of Scripps and the U.S. Geological Survey. "This is
largely natural variability."
But the current heat wave, which has been brewing since May, has
nonetheless raised alarms. It is simmering with sustained intensity,
echoing record high temperatures now wilting Europe and Asia.
"There may be some exacerbating climate change ingredient," Cayan said. "In fact, it is almost certain."
The current high temperatures fit with extremes that have been on an
upward arc for the last century and are in line with computer
projections for more records in the future.
"What we now call extreme events are becoming run-of-the-mill happenings," said Scripps climatologist Tim Barnett.
The first six months of 2006 were the warmest in the United States
since record-keeping began in 1895, according to the National Climatic
Data Center. The 10 hottest years on record have all occurred since
1990, a trend that a majority of scientists say is in large part
attributable to human production of greenhouse gases, which trap heat
in the atmosphere.
All told, the planet has been slowly warming for a century, with
Earth's average temperature rising by 1.6 degrees. In Los Angeles, the
average daytime temperature has increased 3 degrees over the last
century, while nighttime temperatures have increased 7 degrees, records
show.
In 1939, a high of 107 degrees broke all records. By 1955, the record
high was 108 degrees; it crept to 109 degrees by 1963, and in 1990
reached 112 degrees.
Such temperature extremes arise from a cat's cradle of causes, experts
said. The current weather is affected by an extended regional drought
and broader, long-term climate trends that encompass much of the
Northern Hemisphere.
The effects of urban development also play a major role, as thousands
of square miles of dry chaparral are transformed into highways, housing
tracts and strip malls — all of which retain heat.
The immediate cause of the current heat is a lingering
high-pressure system centered over the Four Corners region of the
Southwest, said JPL climatologist William Patzert.
As it slowly turns clockwise at about 15 mph, that immense wheel of air
also sweeps the ocean's warm surface water against the Southern
California coast, eliminating the cooling marine breeze that tempers
the local climate, he said.
An extended drought in the Western states has strengthened the
high-pressure system, while the jet stream, which in a normal year
would help cool the West, has kept north of the Canadian border.
"This heat wave is coast to coast, border to border," Patzert said. "It
has been going on for six weeks now where temperatures have been
abnormally high. Now they are off the scale."
The patterns have come and gone in the past.
In July 1931, sweltering Angelenos bemoaned the 37th straight day of
extreme high temperatures — at that point the longest stretch of hot,
humid local weather in the history of the National Weather Service.
Few recalled that, a generation earlier, as temperature records
shattered in July 1891, perspiring businessmen sought shelter in the
cool of the Grand Opera House and worried that such searing
temperatures might mar efforts to market California's perfect climate
to Easterners.
No one then would have blamed global warming — a concept that did not gain scientific currency until the 1980s.
Since then, scientific understanding has progressed in lock step with a contentious political debate.
The debate eludes resolution because of the difficulty of separating
normal temperature swings from longer trends. In the effort to
understand climate, certainty comes only with the hindsight of
centuries.
The severity of the current heat wave, in which temperatures this month
have reached 100 degrees or more for at least 10 straight days, marks
the first time in 57 years that both Northern and Southern California
have experienced simultaneous, extended high temperatures, California's
Undersecretary for Energy Affairs, Joe Desmond, said Tuesday.
"This is a historic heat wave," Desmond said.
Still, Patzert said of California's weather: "Is that a part of global warming? I don't know."
Some scientists, however, believe it a harbinger of more extreme summers in decades to come.
"People talk about tipping points," said Scripps' Barnett. "We have
gone past it. There is nothing we can do to stop it now. The only
question is how big a hit we are going to take."
Whatever the ultimate scientific truth, this month's weather has been
for many Southern Californians a perceptual tipping point that brought
home the possibility of global warming, just as the fury of Hurricane
Katrina did for the people of New Orleans.
Inside the air-conditioned darkness of the Majestic Crest Theatre in
Westwood, Max Furstenau, 18, was cleaning up after Tuesday's 3 p.m.
showing of "An Inconvenient Truth," in which former Vice President Al
Gore made the case for global warming.
Outside, the weather had finally cooled to the comfortable mid-80s. The
day before had hit 110 degrees, breaking the record of 107 set in 1954.
"I know it's happening," Furstenau said.
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