Christine, you are probably thinking about the National Academy of Sciences report, referred to in the following New York Times Jan. 13 news brief:
National News Briefs; Earth Report Shows Accelerated Warming
Despite conflicts in temperature data, there is strong evidence of an accelerated warming of the Earth's surface during the past 20 years, a panel of the National Academy of Sciences concluded today. Still, the panel hedged on whether the warming wo ...
Sorry, can't give you any more text than that, without paying the NYT $2.75 for the full article. And I ain't about to do that. :>)
Fortunately, however, The Washington Post lets you read any article for free that was published within the last two weeks. And I ran across one about a new (and also disputed)weather theory, which, if true, may complicate the global warming picture.
Climatic Flip, or Blip? U.S. May Be
Entering New Weather Era
By Curt Suplee
Washington Post Staff Writer
Thursday, January 20, 2000; Page A01
The United States may be on the brink of a change in climate
patterns that could last 20 or 30 years, some scientists
believe.
If current temperature conditions in the Pacific Ocean
persist, if an upstart theory of climate cycles proves correct,
and if satellite data released yesterday reflect the start of a
new era, America could be about to experience a
meteorological replay of the 1950s and '60s.
On average, winters are likely to be colder and wetter, but
drought is more probable in the parched Southwest, and the
Southeast could have warmer weather. Storms and snowpack
are likely to increase in the Northwest and Rocky Mountain
states. Northern states will have lower winter temperatures.
More hurricanes will hit the Southeast. There will be fewer El
Ninos but more La Ninas.
All this and more, a growing number of scientists say, could
result from a titanic flip-flop in something called the Pacific
Decadal Oscillation (PDO), a concept so new that it was
named only three years ago and is still the subject of hot
debate.
"There's a lot of controversy about it, even among the guys
who invented it," said Ants Leetmaa, who heads the National
Oceanic and Atmospheric Administration's Climate
Prediction Center. "But I personally tend to think it's
probably real."
According to the theory, the Pacific Ocean switches every 20,
30 or 40 years between two opposite conditions: "warm" and
"cool."
In the warm phase, an abnormally warm wedge of water
appears near the Americas while the Pacific sea surface cools
around the Asian rim from Japan to Australia. This affects
our weather in much the same way as El Nino--the sudden
appearance of unusually warm sea water west of Central
America--and PDO partisans believe the warm phase of the
PDO is in effect an extended and less intense El Nino.
Historical climate data indicate that such warm phases
dominated from 1925 to 1946 and again from 1977 to 1998 or
so, according to scientists at the University of Washington
who first proposed the PDO concept.
The alternative "cold" phase occurs when the sea surface
around the Asian rim gets abnormally warm; at the same
time, the ocean off the western United States is colder than
usual. This leads to weather patterns similar to those
produced by La Nina--the periodic arrival of abnormally cold
Pacific water off Central America. The eastern Pacific is now
in the grip of a particularly long-running La Nina.
Similar cold phases prevailed from 1890 to 1924 and from
1947 to 1976, the researchers found.
A new one may be starting, according to the most recent
images from the U.S.-French TOPEX/Poseidon
ocean-monitoring satellite, said Bill Patzert, a research
oceanographer at the NASA/Caltech Jet Propulsion
Laboratory in Pasadena, Calif.
"We're coming out of a warm PDO pattern, and if it continues
into a cold PDO, certain [weather] tendencies that we've seen
for the past 20 years could potentially reverse themselves,
changing temperature and rainfall patterns around the
planet," he said.
The satellite data, released yesterday, show that sea surfaces
are 3 to 9 inches higher than normal in a giant horseshoe
shape around the western Pacific rim, and the same amount
below normal near Central and South America. Presumably
the height is a function of temperature; water, like other
things, expands as it warms.
The cool-phase conditions were first noticed in mid-1998, and
they have grown clearer in the past 18 months. Leetmaa
suspects the shift began around 1995, if not earlier, based on
worldwide changes in rainfall patterns, hurricane numbers
and other variables. But no one can say for certain.
John M. Wallace of the University of Washington's
department of atmospheric sciences, whose group was
analyzing the PDO before it had a name, said it would take
"something like a whole decade" of data to declare with
confidence that the phase had changed.
"It's very hard to know where you are [in the PDO cycle] at
the time," he said. Even during the now well-established cold
phase of 1947-76, he observed, "we had this long-lived El
Nino in 1958-59. Now we ignore that episode when looking at
the larger record. But at the time, it might have seemed as if
we were entering a warm period."
No one knows why the PDO occurs, although presumably it
has something to do with rhythmic alterations in Pacific
currents.
Survival rates for young salmon are directly tied to
environmental conditions, particularly water temperature.
Lower temperatures favor the fish. So when the PDO is in its
warm phase, salmon populations decline in the Pacific
Northwest but rise in Alaska. During the cool phase, the
pattern reverses. Around the time that researchers published
that finding, a Japanese group found similar evidence,
including tree rings showing changes at 20- to 30-year
intervals.
The PDO has been identified and studied for such a short
time that its worldwide effects are largely unknown. Unlike
El Nino, which has its greatest effect on weather patterns
1,000 miles north and south of the equator, PDO changes are
thought to be felt most strongly at middle latitudes in the
Northern Hemisphere.
But any major rearrangement in the heat distribution in the
Pacific--which covers more than one-third of the Earth's
surface--is certain to cause global changes in wind currents,
jet-stream routes and water content of the air.
Leetmaa believes it is possible that PDO phase affects such
remote events as rainfall in China and the periodic droughts
in the Sahel region of Africa. "Rainfall in the Sahel has been
low for 20 years," Leetmaa said, "but started coming up in
'94."
Locally, a repeat of the 1950s and '60s would mean lower
minimum and maximum temperatures, more snow and more
rain, according to National Weather Service archives. But the
Baltimore-Washington region was drastically less populated,
developed and asphalt-covered in those days, so direct
comparisons could be misleading.
Nathan Mantua, one of the authors of the 1997
PDO-and-salmon study, believes that it is too soon to tell if
the phase has flipped: "It's possible that it's just a blip. Right
now, the No. 1 priority is to figure out what makes it tick.
Why does it exist? Is it predictable in the same way that El
Nino is?" If so, climate researchers agree, it would provide a
hugely valuable method of forecasting broad trends years in
advance, compared with the few months of warning the world
now gets of an impending El Nino or La Nina.
Meanwhile, Wallace said, "even if one can only look back
and see patterns," it is necessary for government planners to
think beyond the short term, especially in cases such as the
fast-growing American Southwest, where water availability is
crucial to the future of the region. "In lots of cases you can
weather a one-year drought very well. But if you're building
a dam, or offering insurance, for example, it's really useful to
know that you can expect runs [of the same kind of weather]
for decades."
© Copyright 2000 The Washington Post Company
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