Heated dispute; Scientists grapple with conflicting measurements but agree that Earth's temperature is on the
rise
By Eric Niiler
Copyright 1998 San Diego Union-Tribune
September 30, 1998
Taking the Earth's vital signs would seem to be an easy task.
Backyard weather-watchers check their thermometers daily, while oceangoing
drifters, weather balloons and orbiting satellites record the planet's pulse
far from human hands.
Every day, these readings are plugged into mathematical models that simulate
the Earth's
complex climate machine. Yet despite the latest technology and fanciest
computer models, scientists still don't understand basic questions about how
the Earth's climate works and, more specifically, the
global warming trend that they believe is under way.
Is this warming -- about 1 degree Fahrenheit since the
late 19th century -- out of the ordinary? If so, is it caused by the waste
gases of global economic activity? And why don't temperature reports from
satellites, weather ballons and ground stations always add up?
At the moment, this past August ranks as the warmest month on record, followed
by July 1998. The warmest years since the late 1800s are 1997, 1990 and 1995.
Indirect measurements indicate that, overall, this century is the hottest in
600 years.
A bit of warming might seem
benign, but the implications of global
climate change are staggering. Scientists already are predicting rising sea levels, coastal
flooding, droughts, heat waves, shifting agricultural growing zones and more
powerful tropical storms that would make this year's El Nino- generated rains
look like a
spring shower.
These events may be in store if the Earth's average temperature rises 2 to 6
degrees in the next century, as predicted by some researchers. The rise is
linked to a doubling of so-called greenhouse gases -- carbon dioxide and other
byproducts of fossil fuel burning --
in the lower atmosphere.
But researchers say gaps in both the measurement and understanding of today's
climate -- as well as the climate of the past -- continue to plague them.
For example, most of the land-based temperature records come only from
meteorological stations in the Northern Hemisphere. Records go back
only a few decades or years in South America, Asia and Africa.
Ice cores that give researchers important clues about the temperature in
Greenland and Antarctica thousands of years ago say nothing about the tropics,
a region where much of the
global warming turmoil may
take place and where the Earth's climate engine gathers heat.
And just getting accurate, up-to-date satellite temperature records for the
past two decades has turned into a scientific brouhaha slugged out in the pages
of academic journals.
"None of the tools we have are great," said Ellen Mosley-Thompson, a climatologist at Ohio State University who
is studying the past
climate through ice-core measurements.
Despite the drawbacks, Thompson believes that by adding up the pieces, a clear
picture of human-induced
climate change is emerging.
"We know the weaknesses in our data and we
present the caveats," Mosley- Thompson said.
"What the public walks away with is that scientists don't know what they're
doing, but science is a constantly evolving process. The longer our records
get, the closer we will get to answering questions to how unique the 20th and
21st century (climate) is. Our records are so
short right now."
Ice, coral and ring tales
To better understand what's happening today, scientists are trying to
reconstruct the climate record of the past. Consistent temperature records
based on thermometer readings go back only about 100 years.
To learn more of the distant past, investigators
must rely on indirect measures: ice cores that trap ancient atmosphere, tree
rings that indicate warm, wet years vs. cooler, drier ones and coral reefs that
capture a temperature signal of the sea surface centuries ago. Other
researchers, meanwhile, dig up
fossilized pollen captured in lake sediments or ancient marine fossils for
meteorological clues.
One of the best records of the paleo-climate, or past climate, are ice cores.
Tiny air bubbles trapped in the vast ice fields of Greenland and Antarctica
contain traces of nitrogen, carbon
dioxide and methane from as far back as 400,000 years. These core bubbles
preserve the past temperature, like a cellar preserving last winter's chill.
To determine historical temperatures, scientists drill several miles into an
ice sheet, extracting a long, thin cylinder of ice that is sliced into
sections and shipped back to labs in airborne coolers.
In a basement laboratory at the Scripps Institution of Oceanography, Jeff
Severinghaus holds up a 4-inch-long, 20,000-year-old hunk of ice. It looks
like frost-covered crud chipped
out of an old icebox.
At $20 million per core drilling, this is
"pretty precious ice," said Severinghaus, a young climatologist who recently came to Scripps from the
University of Rhode Island.
Severinghaus and his colleagues melt the ice in a vacuum chamber to release the
trapped
air. This air is piped through a device called a mass spectrometer to
determine its molecular makeup.
The ratio of argon and nitrogen isotopes in the trapped bubbles gives a proxy
record of how cold it was when the ice formed. Severinghaus recently
discovered that Greenland warmed up
18 degrees in as little as three years at the end of the last ice age, some
11,600 years ago.
Previously, scientists had believed it took thousands of years for Greenland
and the rest of the Northern Hemisphere to thaw out. The quick warming was
probably accompanied by violent,
unstable weather.
Such quick reheating, Severinghaus said,
"would be much more destructive to society than warming that took 50 to 100
years."
Severinghaus' efforts to map out Greenland's prehistoric climate have
implications today. Computer models predicting future
global warming are run using data from the past. Unfortunately, the
models don't always agree with the ice-core record. They underestimate the
strength of past
climate changes and may underestimate the size of future
climate changes.
"Most of the models fail," he said.
"It's a powerful indictment of their reliability. But that said, the models are
getting better."
Upstairs from Severinghaus' lab,
Franco Biondi slices up slabs of dead trees. Under his microscope, he looks
for a pattern of tree rings getting bigger during warm or wet years and smaller
when there is less moisture or cooler.
Biondi has been studying trees from Idaho, California, Arizona, Baja and
mainland Mexico. Each
kind of tree has a different record. He matches recent meteorological records
to recent tree rings to see if they match. If so, he can then go back and use
older rings to measure older climate.
The few remaining Torrey pines just north of La Jolla give a record
stretching back 300 years. Douglas firs in Idaho go back 900 years, and some
Bristlecone pine in the Sierras date back 4,700 years.
Biondi said tree ring studies are best for determining patterns in the climate
rather than actual temperature or
rainfall numbers.
Another drawback is that most tropical trees don't produce rings, like pine
trees. And while some equatorial zones have mountainous regions with trees
producing annual rings, the gaps in the climate record at the tropics continue
to confound researchers.
Of all the climate scientists,
Scripps geophysicist Chris Charles may have one of the more the enjoyable jobs.
He and his colleagues travel around the Pacific, plunge into tropical waters
with mask and fins, and sample coral reefs with a drill. After taking a
sample, they plug the hole with cement to prevent parasites from destroying the
living coral.
Upon returning to Scripps, they grind up small pieces of the coral and zap them
in a mass spectrometer. By comparing ratios of two oxygen isotopes, they get a
precise correlation of the changes in sea surface temperature over the years.
Some corals live 300 to 400
years, long before mariners began taking ocean temperatures on sea voyages.
"Coral is just sitting there bathed in sea water," Charles said.
"So it really is a beautiful archive we're waiting to tap."
Past and present
These indirect measurements -- ice, tree rings and
corals -- are filling in gaps in the the Earth's climate history. In the
technologically advanced 20th century, you would think that scientists would
have nailed down the temperature record. But it has yet to happen.
Merchant and Navy ships began taking consistent readings at the beginning of
the century, but they used
several, sometimes conflicting, methods. British meteorologists began launching
weather balloons to measure the atmosphere in 1948, but their record-keeping
methods weren't consistent, and the readings haven't been reliable as a whole.
Ocean drifters and satellites began scanning the oceans and atmosphere in the
1960s, but
only recently have they been able to cover the entire globe.
"Every data set has its problems," said Rob Quayle, chief of the global climate lab, at the National Climactic
Data Center in Asheville, N.C.
"You need multiple observing systems, and if as a group they are telling about
the same thing, that
gives you added confidence."
Satellites hold out promise as a high-tech way to measure the temperature of
the atmosphere or oceans. They hover above the Earth and can take a wide-
angle snapshot of various environmental indicators.
Since 1979, satellites operated by the National Oceanic and Atmospheric
Administration (NOAA) have been sampling the troposphere, a layer of the
atmosphere that extends from the surface to six miles above it. The orbiting
satellites beam microwaves through this layer, measuring tiny vibrations of
oxygen molecules given off when exposed to the sun's rays.
Land, ocean and deep-ground measurements have risen
in the past century, but this satellite record has bucked that trend. Skeptics
have used this contradiction to bolster their argument that
global warming is fictional, or so insignificant as to not worry about.
Last month, two California scientists looked at the satellite record and found
that the satellites' orbits had decayed by
more than mile as they have circled the globe, throwing off their ability to
measure temperatures near the Earth's surface.
After correcting for the bias, the scientists said the satellite record showed
a slight warming of about .13 degrees per decade. That's compared to the .09
degree per decade cooling
reported earlier.
Kevin Trenberth, a climatologist at the National Center for Atmospheric
Research in Boulder, Colo., noted that individual satellites only operate three
or four years, making direct comparisons over a long time period difficult.
Satellites also drift, wobble, their
instruments go bad (one device was pointed at outer space instead of Earth) and
they are only replaced when they actually fail.
"Satellites are great for giving global perspective, they are absolutely useless
in giving long term trends," Trenberth said.
Trenberth also had harsh words for James
Christy, a former graduate student of his who put together the
"cooling" satellite record along with Roy Spencer of NASA's Marshall Space Flight
Center.
"Somebody besides Spencer and Christy should be doing it," Trenberth said.
"They can't admit they are wrong. The answer they are giving doesn't make sense
with
surface measurements and water vapor measurements."
Christy defends his work. He said he has corrected the correction by the
California scientists and that his new information shows a slight cooling in
the troposphere.
Trenberth
"is not a satellite meteorologist," Christy said.
"He wouldn't understand. The proof of pudding is independent comparisons."
Christy has resubmitted his work to several research groups for peer review and
publication in a journal, the way that scientists validate each other's work.
Many scientists say the lesson of the satellite dispute is that better
instruments are needed to measure
climate change. Satellites have broad coverage, but their
accuracy is in question and clouds or dust can interfere with their sensors.
Drifting buoys take on-site readings of ocean temperature, they are being used
to verify satellite readings. There are now more than 600 such bobbing buoys
-- resembling 30-foot-long socks full of holes -- drifting throughout the
world's oceans.
Scientists recognize that gaps in their knowledge about the climate machine are
being used by critics to stall
global warming treaties, and they are working hard to eliminate them.
Ralph Kahn, a climate scientist at the NASA/Caltech Jet Propulsion Laboratory
in Pasadena, has built
a new satellite device that will measure the Earth's climate when it is
launched next year.
"We aren't measuring temperature accurately enough and in enough places to know
what's going on," he said.
"But it's getting better and we keep diminishing the uncertainties."
Comments on this posting?
Click here to post a public comment on the Trash Talk
Bulletin Board.
Click here to send a private comment to the Junkman.
Material presented on this home page constitutes opinion of Steven J. Milloy.
Copyright © 1998 Steven
J. Milloy. All rights reserved on original material. Material copyrighted by others is used either with permission or under a claim of "fair
use." Site developed and hosted by WestLake
Solutions, Inc.