CCNet, 77/2000 -  18 July 2000

     "So where are the near-Earth asteroids coming from?," asks
     [Bob] McMillan. They must be raining down on us from the main-belt
     asteroids between Mars and Jupiter, he said. Likewise,
     Centaur-class asteroids are raining down from the Kuiper Belt
     beyond Neptune. "So the whole solar system is constantly in change
     and in a state of flux. That's completely different than what was
     thought in the 19th century, which is that these orbits were
          -- Bob McMillan, 17 July 2000

     Lucifer's Hammer
     By Larry Niven and Jerry Pournelle
     Ultra-Condensed by David J. Parker and Samuel Stoddard

     Tim Hamner: I've discovered a comet.
     Scientists: The comet will come close to us.
     Tim Hamner: Will it hit us?
     Scientists: Nah.
     (The comet HITS them, and civilization is DESTROYED.)
     Scientists: Oops.
     THE END



    Harvey Leifert <>

    Valentin Grigore <>

    SpaceDaily, 17 July 2000

    Jens Kieffer-Olsen <>

    Timo Niroma <>



From, 17 July 2000

By Leonard David
17 July 2000

TUCSON, ARIZONA -- At any moment, Planet Earth could be menaced by
potentially devastating asteroids. Although we may not be able to avoid
getting hit, the Spacewatch Project could at least warn of us an
approaching asteroid.

Now being built is a 72-inch (1.8-meter) diameter telescope, to be
situated near the currently working Spacewatch telescope. "That will
make it the largest telescope in the world dedicated full-time to that
exclusive purpose," said Robert McMillan, director of the Spacewatch
Project here at the University of Arizona's Lunar and Planetary
The new telescope will be used exclusively for asteroid searches,
relocating objects that have become, quite literally, lost in space,
and for keeping an eye on the whereabouts of newly found objects.

"That will make it the largest telescope in the world dedicated
full-time to that exclusive purpose," McMillan said.

The Spacewatch Project has been exploring the whole solar system for
some two decades -- from the vicinity of Earth's orbit out to Neptune's
-- to find objects, how they got to be in those orbits and to better
determine how the solar system evolved.

"Right now, we're finding, on average, about two near Earth asteroids
per month," McMillan said.

With the new telescope, along with new electronic devices outfitted to
the existing telescope, the Spacewatch Project enters a new observing

Faster discoveries

"We should be discovering objects much faster, perhaps as many as 20
per month. We'll be busy," McMillan said.

Jim Scotti, a Spacewatch Project researcher, said the more sensitive
upgrades and newer equipment would permit Spacewatch to carry out
studies more effectively.

The ability to detect fainter objects will allow Spacewatch to find
smaller asteroids nearby, as well as smaller and even more
distant bodies in the solar system's outback, Scotti said. With
the larger telescope, completion of the Near Earth Asteroid
survey, including rocks as small as approximately one half mile
(0.8-kilometer-) in size, can be more easily accomplished, he

The main goal of Spacewatch is to spot comets and asteroids that
might be potentially dangerous objects, well before they pose a
threat to Earth.

These big bruisers have bombarded Earth before …and they will
wallop the planet again. It's just a matter of when, Spacewatch
officials admit.

Even now, there are several asteroids that look menacing. They
have orbits that could make them dangerous sometime in the future.

Size does count

As many as 900 large asteroids, more than a half-mile (one
kilometer) in size or greater, float through the inner solar
system and are a possible threat to Earth.

Like many things, in the case of asteroids, size counts too. A
space rock more than half a mile across that slams into Earth
can wreak global havoc.

"One of the challenges to the whole asteroid community is to find
out how many of these objects there really are," said Robert
McMillan, director of the Spacewatch Project here at the
University of Arizona's Lunar and Planetary Laboratory. "Knowing
the number of Earth-approaching asteroids, then we can quantify
the impact hazard," he said.

Atop nearby Kitt Peak, the Steward Observatory 36-inch (0.9 meter)
Spacewatch telescope is busy. Observers using that instrument and
associated equipment are playing the numbers game. They try to
count small objects in the solar system.

The statistics of how many asteroids and comets are found helps to
gauge just how dynamic the planetary neighborhood really is,
McMillan told "You can observe a certain amount of sky,
find a certain amount of objects, then extrapolate that number to
estimate the total size of the population," he said.

Supply and demand

McMillan said that if there was just one supply of near-Earth
asteroids billions of years ago, they would have been all swept up
by now. By crossing the orbits of Mars and Earth, and sometimes
swinging by Venus, asteroids wouldn't stay in their orbits for
very long. They would be scattered away, he said.

"So where are the near-Earth asteroids coming from?," asks
McMillan. They must be raining down on us from the main-belt
asteroids between Mars and Jupiter, he said.

Likewise, Centaur-class asteroids are raining down from the Kuiper
Belt beyond Neptune.

"So the whole solar system is constantly in change and in a state
of flux. That's completely different than what was thought in the
19th century, which is that these orbits were stable," McMillan

"So we're doing science. Sometimes that message doesn't quite get
across. Detecting hazardous asteroids is one of our many roles,"
McMillan said.

Scotti said the work the group carries out is unique. "We are not
just surveying for the next impactor, but we're also trying to
learn just how all of the different populations of small bodies in
the solar system interrelate and what that will tell us about the
formation and evolution of our solar system," he said.

Playing the odds

McMillan and Tom Gehrels, also an astronomer at the university's
Lunar and Planetary Laboratory founded Spacewatch in 1980.

For Gehrels, there is a haunting obligation for the Spacewatch
Project to keep on the lookout for asteroids and comets harmful
to Earth.

"The chances are one in 10,000 that in your lifetime you would see
this [an impact on Earth], and it would be horrific," Gehrels
said. "I do consider it a serious problem in terms of numbers,"
he said.

"We had this idea long before anybody else. Spacewatch was to do
statistics, not to work on hazards. But the hazard aspect came in
immediately," Gehrels said. "Though we didn't realize it in our
guts, our minds had set us on this path, to go after this and take
care of it as part of the statistics work," he said.

Finding funds

Finding objects that might present a hazard to Earth has not been
work fully embraced by the scientific community, Gehrels said.
Back stabbing, outright hatred, and maybe touches of jealousy by
other scientists have been stirred up over the years as the
Spacewatch Project moved forward, he said.

"I've been described as the only astronomer who lies awake over
this problem. And I've admitted to that," Gehrels said. "But the
more precise reason for lying awake is how to get the funding to
do the Spacewatch Project," he said.

The Spacewatch Project, Gehrels said, does not need much money.
Finding a private donor who will support the effort is on the
order of $300,000 a year is all that's needed.

At present, Spacewatch funding is one-half to two-thirds federal
monies, and the rest private foundations and personal
contributions, McMillan said.

"If he doesn't find it, he may go under. It would be like a house
of cards," Gehrels said. "That's been the story right from the
beginning," he said.

Copyright 2000,                  


From Harvey Leifert <>

American Geophysical Union
July 17, 2000
For Immediate Release

Contact: Harvey Leifert
(202) 777-7507

A mystery of Earth's wobble solved: it's the ocean

WASHINGTON - The century old mystery of Earth's "Chandler wobble" has
been solved by a scientist at NASA's Jet Propulsion Laboratory in
Pasadena, California. The Chandler wobble, named for its 1891
discoverer, Seth Carlo Chandler, Jr., an American businessman turned
astronomer, is one of several wobbling motions exhibited by the Earth
as it rotates on its axis, much as a top wobbles as it spins.

Scientists have been particularly intrigued by the Chandler wobble,
since its cause has remained a mystery even though it has been under
observation for over a century. Its period is only around 433 days, or
just 1.2 years, meaning that it takes that amount of time to complete
one wobble. The amplitude of the wobble amounts to about 20 feet at the
North Pole. It has been calculated that the Chandler wobble would be
damped down, or reduced to zero, in just 68 years, unless some force
were constantly acting to reinvigorate it.

But what is that force, or excitation mechanism? Over the years,
various hypotheses have been put forward, such as atmospheric
phenomena, continental water storage (changes in snow cover, river
runoff, lake levels, or reservoir capacities), interaction at the
boundary of Earth's core and its surrounding mantle, and earthquakes.

Writing in the August 1 issue of Geophysical Research Letters, Richard
S. Gross of NASA's Jet Propulsion Laboratory reports that the principal
cause of the Chandler wobble is fluctuating pressure on the bottom of
the ocean, caused by temperature and salinity changes and wind-driven
changes in the circulation of the oceans. He determined this by
applying numerical models of the oceans, which have only recently
become available through the work of other researchers, to data on the
Chandler wobble obtained during the years 1985-1995. Gross calculated
that two-thirds of the Chandler wobble is caused by ocean-bottom
pressure changes and the remaining one-third by fluctuations in
atmospheric pressure. He says that the effect of atmospheric winds and
ocean currents on the wobble was minor.

Gross credits the wide distribution of the data that underlay his
calculations to the creation in 1988 of the International Earth
Rotation Service, which is based in Paris, France. Through its various
bureaus, he writes, IERS enables the kind of interdisciplinary research
that led to his solution of the Chandler wobble mystery. Gross's
research was supported by NASA's Office of Earth Science.

Notes for working press only:

1. The paper, "The excitation of the Chandler wobble," will appear in
the journal, Geophysical Research Letters, volume 27, number 15 (August
1, 2000). The author is Richard S. Gross of the Jet Propulsion
Laboratory, California Institute of Technology, Pasadena, California.

2. Journalists may obtain a copy of this paper (4 pages) on request to
Harvey Leifert, <>. Include your name, title,
publication, address, phone, and fax number.

3. For further information on the science in this paper, journalists
may contact Dr. Gross at JPL: +1(818) 354-4010 or


From Valentin Grigore <>

Hello everybody !

Here is the first E-mail Newsletter with informations about the
2000 International Meteor Conference. This message is sent to the
members of IMO-News Mailing List, so, excuse us if you received for the
second time this IMC 2000 Newsletter. If you want to unsubscribe IMC
2000 News, please, read the instructions from the end of this
Newsletter. Thank you !

Welcome to the last INTERNATIONAL METEOR CONFERENCE of the Millenium
                             ~  IMC 2000 ~
    Pucioasa, Romania, September 21-24, 2000
        IMC 2000 Newsletter, Nr. 1, June 26, 2000

Born from the darkness,
It is a meteor, my friends.
Light through self – sacrifice,
Challenge for our beings…  
And joy for our eyes.
                             ~Andrei Dorian Gheorghe~ 

Dear Friends, 

As you probable know, it was decided at the 1999 IMC in Frasso   
Sabino, Italy, that the last International Meteor Conference of the  
Millenium to be held at Pucioasa, Romania, from September 21-24,

Every year, the International Meteor Conference (IMC)-the yearly 
conference of the International Meteor 
is a great event. 

This year, the 2000 IMC will be held around the 2000 autumn equinox. It
will be organized by the Romanian Society for Meteors and Astronomy
(SARM), having the cooperation of the mayoralty of Pucioasa. 
1. Informations about SARM and Pucioasa

The SARM is an astronomical youth organization, the only national
astronomical society in Romania and the 2nd in the Romanian history,
after the one created by Victor Anestin in 1908. The SARM founded the
Romanian meteor work. Its activity is divided into 5 deptartaments and
have 11 brances in Romania and over 200 members: amateurs and
professional astronomers, students, school-pupils, teachers,
researchers, culture and art people, journalists, teenagers with varied
preocupations, astronomical clubs and youth associations.(More about
SARM can be find on the IMC 2000 website). Pucioasa is a little town,
situated at 400 m altitude, on the hills of South Carpathian Mountains,
at 100 km far away from Bucharest, the Capital of Romania. It have over
460 years of recorded existence and 170 years of spa resort activity. 
The connections with Bucharest and the main Romanian cities are very
good and they are made by direct trains and buses.

2. Conference conditions

For the IMC 2000, we will offer an additional free shuttle bus from 
Bucharest to Pucioasa wich will collect the  participants from airport
and train station in Bucharest. Please, inform us if you need more
imformations about traveling conections. The accommodation will be in
Hotel Ceres with double rooms. All meals will be served at the
restaurant of the hotel (you must inform us if you need special
vegetarian food). The conference site, located at 150 m far away from
hotel, is the new building of the Pucioasa Cultural Center, having a
hall of aproximately 200 places, all facilities and some good places
and additional rooms for poster presentation. 

3. Probable program

Thursday, September 21, will be the first day of the IMC 2000. Till 3
pm local time we will collect the participants in Bucharest from
airport/rail station. Then, our bus will start to Pucioasa, but before 
our arriving here, crossing town Targoviste (the former Capital of
Romanian Land) we will stop to do a short visit and a group photo  at
the Chindia Tower (Dracula’s Tower), near the ruins of the Princely
Court Palace (Old Court). The conference will be officially open after
the dinner, and will be followed by a special ceremony. As usual, there
will be an excursion at the IMC. Two places will be visited on the
trip, on September 23. The first one is the New Jerusalem Monastery,
just near Pucioasa, a special place where the God’s Word are speaking
from heaven starting with 1955! Here is a very interesting gallery of
picture, sculpture and traditional art combined with modern elements,
too. The second place is situated in the mountain resort Sinaia. Here,
Prince Carol of Hohenzollern-Sigmaringen (became the King Carol I of
Romania-founder of modern Romania) started the building of the Peles
Castle in 1873, after the drawings of the architect Wilhelm Doderer of
the German school of architecture. A masterpiece of architecture in
German neo-Renaissance style, the castle was finished in 1883, although
some extensions were added between 1893-1914. Peles Castle has had
electricity and central heating since 1883! Part of it is decorated in
Florentine style. The Entrance hall has a very tall ceiling, made of
glass, and is aired by sliding it open with a remote control device
built in 1911. 2000 different faces chiseled in wood and plenty of
paintings are there to be seen on the walls. Rare furniture, sculptures
and stained glass windows give immense satisfaction to the eye of the
visitor. Very few places in Europe can match this display of exquisite
art and architecture of enormous artistic value. Peles Castle is former
summer royal residence of Kings of Romania. Peles has nearby two
smaller brothers: Pelisorul and Foisorul; they are also fascinating

The SARM wishes that the participants to this last IMC of the
millennium perceive this event also as a  holiday. In this respect, the
walls of the conference hall will be  adorned with astronomical photos,
graphics, poems, computer art, pictures, sculptures, etc. The holiday
character will be strengthened by post-dinner meteor shows in which the
SARM will offer to the participants live electronic and folk music,
poetry, drama, mask dance,  humor and even an astral fashion show. It
is interesting to note that several cultural  organizations in the UK
and the US have taken interest in the artistical part of the IMC. So,
the last evening  (September 23) will have an international character
one, for which we are  waiting for other initiatives from IMO members.
We also enjoy a lot of interest from the Romanian media and the
town of Pucioasa. We are sure that all our  plans will become
reality and hope you will not miss this IMC holiday.

4. IMC 2000 registration

The full conference fee is 170 DEM, and covers accommodation in double
rooms, meals, and a copy of the proceedings. Please send the full fee
or a prepayment of at least 100 DEM to Ina Rendtel (see payment
instructions at Please use the
predefined form for registering. Please read the registration
instructions ( and join now !
We intend to offer a reduced price for people who might have problems
paying the full fee. So, a reduced fee of 100 DEM will be applied on
request to the cases where it is necessary. Please, contact in this
sense the local organizing committee soon ( or Also, inform the Local Organizing Committee  about
your requisite equipment for your contributions to the program. E-mail
us for any questions, informations or some special requirements. If you
want to stay some days before or after the IMC in Pucioasa, inform us
for arrangement. Please, start your registration as soon as you can,
because Pucioasa is a spa town, and we must do reservations a lot of
time before conference. Romania is a beautiful country. If you want to
see more in Romania after conference days, inform us and we will try to
do arangements for trip transport and accomodations.

5. The IMC 2000 on the web

The official website of IMC 2000 is available at the next address
with a mirror at
Here you can find more information about SARM, about the conference
place, about Romania and useful informations traveling in Romania. And
a lot of beautiful images! Soon, this website will be completed with
new informations and images.  
On the IMC 2000 web site are 7 main links:
-sarm: here you can find some informations about SARM and its activity;
- imo: here is a link to the main site of the IMO homepage;
- pucioasa: a short presentation of Pucioasa, the town of IMC 2000;
- imc 2000: informations about conference. Soon here will be made
more links to the other interesting websites;
- romania: complex informations about Romania and very good links;
- gallery: here you can find informations and links about very
interesting places in Romania and many nice pictures, more of them made
by SARM members. Now, here are available the next links: Carpathian
Mountains, Danube Delta, Bucharest and Targoviste.
- utils: here is a page with useful links to find informations traveling
in Romania: airports, railstations, ways, visas, currency,
authorities, embbassy, etc.

*** *** *** *** *** ***
Valentin GRIGORE
SARM President
CP 14, OP 1,
Targoviste 0200,
phone: +40 92 829034
fax:+40 45 214389

Visit the 2000 International Meteor Conference web site


From SpaceDaily, 17 July 2000

Cohen Claims Iran Could Accelerate Missile Plans

by Jim Mannion

Hickam AFB (AFP) July 17, 2000 - US Defense Secretary William Cohen
warned Monday of the risk of an accelerated pace of missile development
by Iran in the wake of its successful Shahab 3 missile test.

"I think any time you have success in a particular missile system, it
gives you confidence to move forward with more tests with greater
capability," Cohen said.

"It has a way of growing almost exponentially," he told reporters as he
flew home at the end of a weeklong trip to China and Australia.

Iran announced Saturday that it successfully tested the Shahab 3, a
medium range missile that US officials say failed in its first flight
test in 1998.

The missile's range, estimated at 1,300 kilometers (800 miles), would
put Israel within striking range but not the United States or Europe.

Nevertheless, Cohen said the test underscored the need for a national
missile defense (NMD) system capable of protecting the United States
against a limited attack by countries like North Korea and Iran.

"I think this is an issue that's not going to go away with the
elections," he said.

He said "if there is any delay in the program, then another president
will have to face it at some point because the threat is going to




From Jens Kieffer-Olsen <>

Dear Benny Peiser,

Since the heading you gave my recent letter on the Torino Scale failed
to reflect the point I tried to make, I obviously wasn't expressing my
viewpoint very well :-)

In the light of Jonathan Tate's below remark I meant to defend
professor Binzel's scale in its attempt to provide a one-dimensional
measure of danger. On a different note, however, I also stressed my
view that the scale should be seen to serve a political purpose rather
than a scientific one.

In order to save time before averting a disaster the scale should go
one step further than assigning a measure of danger, it should
translate the danger level into budgetary language spoken by
politicians. Otherwise, left in limbo between scientists and newsmen,
it could earn itself the nick-name 'Casino Scale'.   

Jonathan Tate <> wrote:

> There is obviously no ideal translation of this multidimensional
> problem into a simple one (or two) dimensional system.

Jens Kieffer-Olsen, M.Sc.(Elec.Eng.)
Slagelse, Denmark 


From Timo Niroma <>

Dear Benny,

There are two nagging questions in the search for extraterrestrial
life. The first is why has nobody sent any message to our civilization?
The other is, why has nobody visited our planet in the past billions of

One can of course answer that messages have been sent and there have
been visits, we just haven't noticed either because we don't know what
to search, don't identify what we have found or somebody who has found
us, tries to hide himself.

So I don't take any stand on the probability of these possibilities,
but try only think about the possibility that we really are alone here.
The "here" can mean as well our galaxy or whole universe or a smaller
part of these.

So I try to answer two questions: is it possible that we are alone here
and how possible it is?

Since at least ten years we have known that space abounds with
complicate molecules, some of which are the building blocks of life.
Even comets and clouds from which stars and planets are born contain
these, alcohol and proto-proteins, but it now seems possible that even
the galactic interstellar near-void can contain these. So when stars
and planets condense, they have as their building blocks besides
hydrogen, helium, stone and iron also something that gives  life its
building blocks. What a mighty shift of paradigm. Don't ask where the
life came, it has always been here and everywhere.

Now of course the next question goes, what do we define as life?

Surely bacteria, and why not viruses, maybe some form of nanomicrobia
that we do not know of. Or maybe we do, at least some scientists have
argued seeing this kind of proto-life in Martian meteorites, Australian
stones and in labs.

Now let's take as our starting point bacteria-like life. If we consider
bacteria with their DNA as very advanced form of life, we could expect
that it is not everywhere, but still at many places. A planet like
Earth with all the hundreds of needed parameters for it to be a
suitable place for bacteria-like life would abound from million to
billion in our galaxy (I would prefer rather the million than the
billion, which is rather low, but in case you differ, that's okay).

When the Earth was 4 billion years old (87 % per cent of its lifetime
until today), it had only carried bacteria and the odds were good that
it remains indefinitely (that is until the conditions here become
unbearable for any form of  life) a place for bacteria. Something
however happened 800 to 600 million years ago. The Earth froze from
poles to equator. Probably that was the kind of crises that forced the
bacteria to ally with each other instead of fighting for survival. That
meant that some bacteria specified themselves into particular functions
and not only that, but grew as colonies that were tightly coupled, in
fact so tightly, that the colonies began to look like proto-animals and

What probability do we give to this change? One against a million? That
would leave one planet with multicellular life per galaxy in a galaxy
like our own. Or a thousand if you so will.

Some scientists argue that such kind of proto-multicellular life
existed already some billion years ago. Maybe. But their evidence hints
to loosely-coupled colonies not a proto-multicellular life in a tightly
sense. The pre-Cambrian Ediacara-fauna showed the first signs of
diversification gone so far that the whole character of life on Earth
had radically changed. Besides bacteria Earth now carried on its
surface multicellular life. That happened nearly 600 million years ago,
and has continued without interruption since then covering 12% of
Earth's age till today. To be honest, the multicellular life almost
vanished in a huge catastrophe some 250 million years ago, when 96% of
the species was wiped for a reason unknown. Whatever happened, the
Earth was a warm, totally iceless place to live and the dinosaurs
became the dominant form of life, at least when looked without a

Dinosaurs lived here almost 200 million years, but they did not develop
any culture, at least in the form that we call a civilization. They
would have had time for that, but obviously they had no need for a
culture. So we can have a guess that there are one planet per our kind
of galaxy that houses dinosaurs or other creatures that do not develop
any culture. Or a thousand per our type of galaxy.

As we all know the long and prosperous dinosaur time came to a very
sudden end 65 million years ago because of pure chance, when a piece of
cosmic debris collided with Earth.  

Earth had existed for 98.6% of its lifetime until today when this
happened. What are the odds this or some other kind of a sudden change
moves a planet to a direction that Earth took since. One in thousand?
One in million? That leaves one planet on one galaxy per thousand
galaxies with life striving towards intelligent life. Or at most one
planet per galaxy. Assuming of course that the harsher conditions favor
intelligence as they did some 600 million years ago.

And assuming that when great apes diversified to gorillas, chimpanzees
and australopithecines, one or several of these would some day achieve
the maturity to build a culture. And to build a technological culture
that is capable of knowing its place in the universe and capable of

Where was I. One planet in one galaxy per a million galaxies?

After all, it seems that we probably really are not alone. But the
others are far, too far our imagination to grasp it. But they are
there. The Universe is so huge, they got to be. But hopelessly far
to be reachable or us to be observed by them.

Greetings anyway.

Timo Niroma


Contact: James E. Kloeppel, Physical Sciences Editor
University of Illinois at Urbana-Champaign

Protracted cooling could camouflage effects of global warming

CHAMPAIGN, Ill. -- The human contribution to global warming is clearly
present and must be controlled, say researchers at the University of
Illinois. But there is also another, as-yet-unexplained, cyclic
contribution that has important implications for monitoring future
climate change.

"Appearances can indeed be deceiving," said Michael Schlesinger, a UI
atmospheric scientist. "If global warming doesn't persist year after
year, we shouldn't be fooled into thinking that human effects are no
longer of concern. There is something else at work here that we don't
yet fully comprehend."

Using a simple climate/ocean model, Schlesinger and his wife, Natalia
Andronova -- also an atmospheric scientist at the UI -- calculated the
contributions to the observed changes in global-mean, near-surface
temperature caused by human and volcano forcing, putative variations in
the irradiance of the sun, and the residual temperature change for the
years 1856-1997. The researchers published their results in the July 15
issue of Geophysical Research Letters.

"We found that while the human effect has steadily increased -- and is
now the dominant external factor -- there also is a residual factor at
work within the climate system," Schlesinger said. "This factor played
a significant role in the warmings observed during 1904-1944 and

During both periods, putative variations in solar output played only a
minor role in the observed temperature change, the researchers say.
Volcanoes were similarly dismissed as the predominant cause.

"Some scientists have conjectured that since there were more volcanoes
in the 19th century than in the 20th century, the observed warming
trend was due to a decrease in volcanic activity," Andronova said. "But
that is not the explanation we came up with. Although volcanic forcing
does contribute during 1904-1944, the residual factor is much larger."

The warming observed during 1976-1990 was nearly equally due to human
effects and to the residual factor, with volcanoes contributing a
cooling, and the sun at most a small warming, Schlesinger said. "The
role of the residual factor is even more dominant during 1944-1976,
when the human-induced warming was in opposition to the observed

One plausible explanation for the residual factor was first proposed by
Schlesinger and his graduate student Navin Ramankutty six years ago. In
the Feb. 24, 1994, issue of Nature, the researchers identified a
temperature oscillation that occurred over the North Atlantic Ocean and
its adjacent land areas. The oscillation -- which has a period
of 65-70 years -- periodically warms and cools the atmosphere, thus
sometimes contributing to and sometimes counteracting the greenhouse

"This means there is a very good chance that the present warming will
turn around and we will again experience a protracted period of
cooling," Schlesinger said. "If we do see that, we should not conclude
that the human effect on climate is small or nonexistent -- or that we
have eliminated the problem -- and go back to 'business as usual.' We
need to be far more intelligent in our response."

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