Four weeks ago in Southern California, Santa Ana winds threatened to
drive two fires in Simi Valley — the Porter Ranch and the Sesnon Fire —
on a path through the sun-baked hills towards the ocean. But instead of
building in strength and destructiveness, as the winds often have in
the past, the Santa Anas died down after a couple of days, much to the
relief of firefighters and homeowners in the area.

Could this diminution of wind be traced to global warming?

Climatologists
analyze massive sets of data gathered over decades of observation, so a
trend cannot cause a single weather event, in much the same way that
medical researchers can document the risk of smoking, but doctors
cannot link a patient’s lung cancer to a single cigarette. But
climatologists are developing a new understanding of the factors that
drive the Santa Anas, and a team of researchers at UCLA is reporting
evidence that global warming has already brought down the risk of the
most powerful of Santa Ana winds, which are perhaps the most dangerous
annual natural event in Southern California.

Although the paper
has yet to be published in a peer-reviewed scientific journal, Alex
Hall, research spokesman, said his team expects to see it accepted in a
prominent journal next year, and his team is scheduled to present their
results at the state of California’s annual climate change conference
next September.

The
UCLA researchers are confident in their findings because the underlying
conditions that create the most powerful of Santa Ana winds have been
well documented both observationally and in equations. As these fall
and winter winds roar through mountain passes, in areas such as Simi
Valley, they are powered by a spillover effect from a huge dome of high
pressure air that builds up in the high desert area known as the Great
Basin, in eastern California, Nevada and Utah.

The vast
airflows are drawn to low-pressure areas to be found over the ocean off
the coast near Los Angeles, like water in a stream moving downhill.

But
it’s not just the difference in elevation and air pressure between the
high desert and the ocean that fuels these winds. “Temperature forcing”
also plays a crucial role, and as the land warms more quickly than in
the past, in the fall and early winter, this forcing loses some of its
power. With a physics calculation, Hall’s team finds that this factor
has fallen by about one-third, resulting in a slow but steady downtrend
in the most dangerous winds.

“This is not a small effect,” Hall
said. “It’s a well-known fact that the cool air that forms over the
desert at night is part of the Santa Ana condition, and so, as the
interior of California warms, the difference between the desert and the
ocean air pressures is reduced. That’s why we’re seeing fewer Santa Ana
conditions over Southern California, and why we should continue to see
fewer until the warming of the ocean catches up to the warming of the
land, which won’t be until sometime in the 22nd century.”

Ventura
County meteorologist Terry Schaeffer, who has been forecasting weather
for local farmers since l976, buys Hall’s argument, although he
cautions that the dataset may not be big enough to draw firm
conclusions yet.

“It does make sense, and I think California in
general is going to come out better than the desert southwest,” he
said. “In recent years, the Santa Anas have definitely been weaker, and
have been occurring later in the season. It’s a logical pattern, and
the data points in that direction, but it’s too soon to know for sure
yet.”

Hall points out that with this reduction of wildfire risk will come other changes that may not be so beneficial.

 “When
fires aren’t burning, which is most of the time, these winds bring
pleasant summer-like weather to the area, and they improve air quality
because they blow polluted air out over the ocean,” he said. “They also
play a role in maintaining the productivity of marine ecosystems in the
Southern California Bight by depositing mineral nutrients from the
desert to the ocean surface.  So I don’t view this as “good” or “bad”
news.”

Will global warming lead to cool coastal summers?

Hall’s
team is preparing to present their results next year to a state-funded
scientific research group, the California Climate Change Research
Center, which hosts an annual conference. A paper presented at the
conference this year by a team led by Robert Bornstein at San Jose State, working with Prof. Jorge Gonzalez at Santa Clara, and grad student Bereket Lebassi, found solid evidence over the last 30 years that as the interior
of California warms more quickly in the summer, it pulls cool air from
the ocean inland more forcefully than in the past, resulting in
slightly cooler conditions along the coast.

This is another trend that is expected to strengthen.

“The
world is warming, but it’s not a uniform process, not like an oven,”
Bornstein said. “The warming will bring a redistribution of pressure
systems and wind patterns, and one of those secondary mechanisms will
be stronger sea breezes along the California coast in the summer.”

[Figure above: warming shown in red dots: cooling in blue dots. Note cooling in Bay Area.]

Bornstein
readily admits that this is not a new idea. Weather experts have long
known that the fogginess that develops along the California coast is
driven by a thermal low born of the heat that develops in the summer in
the San Joaquin and other interior valleys. As the winds circulate in a
huge wheel counterclockwise from the land over the ocean, they drag on
top of the ocean, bringing cold water from the ocean floor toward the
surface. The onshore winds pass over this cold upwelling, forming fog.
As the thermal low in the interior pulls the winds a little faster, the
process is intensified, resulting in increased fogginess, which has
already slightly dropped the maximum daytime temperature along the
coast in the summer by about 1 degree Fahrenheit per decade.

 “We
had a hunch that something like this was happening already,” Bornstein
said. “I’ve been showing graphs on this effect to my students for 15
years. But it wasn’t until we started mapping the temperature declines
that the pattern along the coast popped out.”

Bornstein believes
that the intensified sea breezes will push deeper into Ventura County
in the summer than in the past in areas below about 1,000 feet of
elevation, and has already documented this effect in the Bay Area and
in the Los Angeles basin.

Ventura county meteorologist Schaeffer finds this argument convincing as well.

 “We
haven’t had any really hot summers in years,” he said. “I can remember
years in the past when it was actually hotter in the summer along the
coast than in some inland areas like Piru.”

Bornstein’s paper has
been submitted to Climate, the most prestigious scientific journal in
the field, and has a good chance of being published in spring next
year, but already has stirred up excitement in the field. He is meeting
with state officials to work on new temperature estimate maps that he
believes will show a reduced need for air conditioning in coastal
cities such as Los Angeles, and a slowdown in the production of smog,
which thrives on high temperatures.

Smog levels already falling sharply in Ventura County

Due
to efforts to reduce emissions of smog-producing chemicals, Ventura
County, already in the last 15 years, has seen a steady decline in smog
levels. According to the Ventura County Air Pollution Control District,
which was founded in l968, last year the air in the county was the
cleanest ever in its recorded history. Despite doubling its population
over the last 35 years, the number of days in which the county as a
whole exceeded the Federal standards for lung-damaging ozone fell
almost to zero, when many years in the l970s it exceeded that standard
over 100 days a year.

“My primary concern has always been
ozone,” said Mike Villegas, air pollution control district official.
“Coastal areas such as Ventura and Oxnard have not exceeded the Federal
standards for some time, but in our inland valleys, such as the Ojai,
Conejo and Simi Valleys, it’s still an issue. One factor that drives
the ozone reaction is temperature, so a slight cooling would have a
modestly helpful effect.”

Bornstein’s team hasn’t looked
closely at the entire state of California, but estimates that the
slight cooling he has found in the Bay Area and in Los Angeles would be
seen elsewhere in the state in the areas in which the sea breezes
dominate the local climate. These are zones 22-24, according to the
climate maps produced by the University of California for Sunset
magazine, where the ocean influence prevails at least 85 percent of the
time, and include Oxnard, Ventura and Camarillo, but not Ojai, Simi
Valley or most of Moorpark.

Villegas is nonetheless confident
that air pollution in the county will continue to decline due to
ongoing efforts to reduce smog-producing emissions. As one example,
Villegas points to new Federal standards to reduce emissions from
oceangoing ships, which contribute a surprisingly high percentage of
the nitrogen oxides (NOX) that help make smog when heated in the air —
about 17 percent of the NOX found in Ventura County, according to his
estimates.

Some good news about temperature, but what about water?

To
climatologists, both these changes — the slightly cooler summers along
the California coast, and the reduction of the worst of the Santa Ana
winds — are considered local effects. Experts in the field stress that
the larger effects of global warming on a regional level may overwhelm
whatever good news it brings to a specific town.

Kevin
Trenberth, an internationally recognized expert who leads a research
team at the National Center for Atmospheric Research, and who testified
before Congress earlier this year on global warming, has a phrase for
the future of the American southwest — “the wets will get wetter and
the dries will get drier.”

In an interview, he explained that
“coastal regions may benefit from sea breezes, as they always have, but
will be hard hit by rising sea level, occasional storm surges and
erosion, perhaps associated with an El Niño event, and the rains can be
exceedingly hard when they do come, owing to more evaporation and water
vapor in the atmosphere.”

Ventura
County has had a relatively quiet couple of years on the storm front,
but will not soon forget the devastating rains of January 2005,
considered the worst in decades, which severely damaged roads and
highways throughout the county, and contributed mightily to the deaths
of 10 people in La Conchita, buried under a collapsing cliff.

Kelly
Redmond of the Desert Research Institute in Reno, another highly
regarded climatologist, said in an interview that those storms were
“not inconsistent with” global warming, although he stressed that any
one storm cannot be attributed to an overall trend.                                                                                                                  

Redmond
agrees with Trenberth that the prospects for drought in the
Southwestern region are alarming — not for one reason, but for many
different reasons.

For one, most Californians depend on water
from the snowpack that builds up in the winter in the Sierra Nevada and
melts over the course of the spring and summer. Many climatological
studies have shown that as the planet warms, that snow will melt
faster. Worse, increasing amounts of precipitation in the mountains
will likely fall as rain, or as rain on snow. This could lead to
flooding in the spring, and water shortages in the long California
summers and falls.

Separately, climatologists have found a
long-term trend toward the cool dry La Niña pattern that tends to make
for drought. Even more troubling, scientists who study climates of the
past have found strong evidence of what they call “megadroughts”—
droughts lasting as long as 150 years, also linked to La Niña. Richard
Seager, who leads a research team at Columbia, published a paper in
Science magazine in 2005 arguing that a long-term drought has already
begun, and projecting that by 2050 the region as a whole will be as
drought-stricken as Oklahoma was in the Dust Bowl.

What to do?
Bill Patzert, the irreverent climatologist who works with NASA and is
widely considered the best forecaster in Southern California, argues
that the time has come to lessen stress on the system by reducing
population growth and immigration, but admits, “I’m the only one
talking about that.”

The answers, in other words, are still blowing in the wind.