Plumbing the Depths: Lamont-Doherty scientists explore the oceans with their floating lab aboard the research vessel, RV Ewing. Photo courtesy of Lamont-Doherty Observatory.

NEW YORK--Friends, I'm on the George Washington Bridge, crossing the Hudson River. Ahead looms the escarpment of the Palisades, the ancient volcanic portals to the rest of the continent. I'm on my way up route 9W about 15 miles to the headquarters of the renown geophysical research institution, Lamont-Doherty Earth Observatory . LDEO is part of Columbia University, but it's lab is the world in all its physical manifestations. It's mission is to understand how the earth works. For the next month I'll be traversing the Hudson to enter some of Lamont-Doherty's diverse dimensions that begin at base level: earth, sky, wind and water. You are welcome to come along, comment, ask questions and suggest territories of the Earth sciences you'd like to explore. --Kathleen Stein

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Celestial Mechanics & Global Warming

This is the last part of my continuing conversation with Lamont's Wally Broecker on what I think is the closest construct of a "unified theory of global climate" that anyone's put together (see two previous posts). Here's Wally on the role of the orbiting bodies on the Earth's climate; that is, do celestial mechanics affect abrupt climatic changes?

WB: There's no doubt the Earth's climate has been infuenced by these things all the way back. How do you explain these various time-scale phenomena? Of all the things that should be affected by these Malankovitch Cycles, is the strength of the monsoon, especially the Asian Monsoon, that depends on the heating and cooling of the Great Tibetan Plateau, the biggest on earth. In the Malankovitch cycles the annual radiation changes: more sunlight in certain summers and correspondingly less the rest of the year. That change is rather large, over 15 percent. Of course the monsoons are critical for moving water around. I'd say one reason you see that 23,000 year cycle in the [climate] record is because of the monsoons and water vapor.

The 100,000 year cycle, we don't know what it is. The ice volume builds up over 100,000 years, fluctuates somewhat, crashes and builds up, then crashes. Perhaps more people are thinking it's an internal cycle, that the Earth, like a lot of systems, just tends to drift to a point where it drifts too far, then there's a self-correction that pushes it back. Those crashes come at times of prominent summer radiation in the Northern Hemisphere, which would be right where North Atlantic deep water forms. Something about these warm summers seem to pretrigger it, like noise in an oscillator will tend to shorten the length of the oscillation cycle. Something will just flip during one of those high peaks.

But people might say without the Malankovitch Cycles you wouldn't get the tendency to drift, that they maybe coupled together some way. They think the climate change is the sum of various frequencies, and the abrupt changes are sort of noise on that, not too important. I think the opposite: the abrupt changes bring about most of the change; that for some reason the Earth system's preferred state tends to go along with the Malankovitch Cycles. The two go together, and the aburpt changes are somehow being paced by the Malankovitch, orbital cycles. In my book, The Glacial World According to Wally, I lay out a possible explanation in which climatic change is entirely water vapor. But, you know, it's real speculative.

Sent By:Kathleen Stein on Tuesday, February 4, 1997 at 12:31:31.

Playing Russian Roulette With the Climate

I'm talking with geochemist Wallace S. Broecker on the subject of global climate change and its impact on human life. (See previous post).

Q: Can we predict Where We're Going?

WB: I don't think we ever can. The models are our best tool but they have about a 30 percent likelihood of being useful, and there's a 70 percent likelihood something else will happen. Maybe Lindzen [MIT critic of global warming] is right, and the whole thing will be a bust; there won't be any warming at all. Or maybe the warming will be bigger. Or this push will force the climate into another state of operation entirely. That would be horrible, because it would happen just as the planet really got bursting with people. The cities are in trouble, and we have global terror. So if, in the midst of all this, we have one of those climate changes, whether warmer or colder, that would be terrible!

As shown in the Greenland Ice cores, the system flickered when the climate jumped back and forth and then stabilized. So there might be a 20 or 30 year period where the climate was going all over the place. Predicting what to grow, where, how to keep up with food distribution to all those people with such changing climate would be very, very difficult. In a sense we're playing Russian Roulette with climate. You know, we're putting those charges in the barrel and we're spinning it around. One of them maybe the bad one. And another may be the Lindzen one where we get no big change. We're just have to wait and see. But the take-home message is we better be prepared for trouble.

If the global warming were regular and just too big, we could cool the planet by adding SO2 in the stratosphere. It's possible, although not a nice thing to think about. If the Tropics are too damn warm, you know there will be a demand to do something about it -- you can't just fry all the people in the Tropics. I'd think a 3 degrees warming there would be pretty miserable.

Q: In that instance, the people in northern clmates might like the warming. We could have some "heat wars."

WB: Perhaps, depending on where you lived. But I think nobody would be in favor of rapid fluctuations because that would put every business in jeopardy from skiing to farming.

Q: What about rising sea levels?

WB: Warming up the ocean can raise the sea level a meter, and in Bangladesh and some other places that would make a hell of an impact. Of course if the West Antarctic Ice Sheet surged out, that would have a really big impact. But with abrupt climate change, the chances of a rapid run out of the West Antarctic ice are small. But are they 10 percent? One in a 100? One in a 1000? That's the problem. It's not highly probable and neither is likely until toward the next century. And it's hard to say with Antarctica.

Q: Can you speak candidly to the world about overpopulation?

WB: It's such a complicated issue. Now that women's right has come into it, that's a big part of the solution. But I worry that educating people is moving at this pace [holds thumb and finger an inch apart] and population is moving at this pace [spreads arms wide]. Are we realistic in saying we can regulate population growth in a gentle way? I'm not convinced. On the other hand, besides saying it's a huge problem, it's hard to say what to do. It's a little like the CO2 problem which I understand better. We can't regulate CO2, it's too important an ingredient of our society. Can we regulate population effectively? It may be too important a part of people's personal freedom. But I swear: Population growth will be at the root of all our problems.

Somebody asked me what to do at a lecture and I said, `The first thing is lock up the Pope.' But he did admit recently something about including evolution in Genesis. So maybe he'll have another stroke of Words From God pronouncing that population growth isn't good.

Sent By:Kathleen Stein on Monday, February 3, 1997 at 13:13:14.

The Global Climate: A Unified Theory?

In 1996 Wallace S. Broecker, Newberry Professor of Geology, received the Blue Planet Prize for achievements in global research. Over a decade ago he recognized the presence of a "great conveyor belt" of ocean currents encircling the earth that play a major role in controlling climate. He has studied gas exchanges between ocean and atmosphere and traced carbon as it cycles through the Earth's chemical, physical and biological systems. In May, Broecker presented evidence moisture levels in Earth's atmosphere in the Tropics dropped considerably during the last ice age from 70,000 to 10,000 years ago, along with average temperature in the region. Water vapor is a more efficient heat-trapping greenhouse gas than carbon dioxide, he said, and reductions in water vapor in the atmosphere could cause planetary cooling. (Conversely, increased water vapor could serve to trap heat and warm up the planet -- and quickly.) Changes in water vapor, Broecker suggests, could force the abrupt climate changes that appear to have occurred synchronously in northern and southern hemispheres. Water vapor changes have been considered as a secondary reaction to global warming or cooling. "We opt to turn this thinking around and make water vapor the driver that changes global temperatures," he said.

A few days ago I met with Broecker in his office to consider the prospects of the planet. The entire Lamont campus was embraced in a dense, wet fog, and it was not hard to conceptualize the power of water vapor on a grand scale.

Q: You have no doubt about global increase in carbon dioxide?

WB: The rise in CO2 will continue no matter what kind of legislation we enact, because even at the optimistic 1990 assessment that usage will level off at six gigatons a year of carbon burn. An enormous amount! It will continue to go up for 100 years. But I don't think there's a hope in hell that worldwide leveling off will happen. The developing countries will industrialize and burn more coal. It's going to go up.

Q: You've considered the possibility that a build-up in greenhouse gases might trigger a rapid reorganization of the ocean "conveyor-belt" system, driven by a change in atmospheric water vapor. But Richard Lindzen of MIT -- an adamant critic of global warming -- says water vapor has little significance in augmenting a greenhouse effect.

WB: Lindzen's main complaint is he doesn't think water vapor will act as a positive feedback to warm the atmosphere. He thinks it will act as a negative feedback [to cool it]. Well, if in a model you just raise atmospheric CO2 to double, that would come out to warm the planet about 1/2 degree, that's a back of the envelope calculation. But if you heat the atmosphere, it can hold more water, so that creates values from 2.5 degrees up to 5 degrees, depending on variable feedbacks of more and more water.

Q: Lindzen does not accept the result of climate modeling.

WB: Lindzen says, without using any models, just intuition, this isn't going to happen. That water vapor will not enhance warming. He says warming may in fact dry out the atmosphere, drive the circulation harder. Some people think water sort of diffuses from the tropics into down-welling air, and the faster you run it, the less time it will have to diffuse. And the tendency will be to dry out the desert regions of the world. So Lindzen has a point. There is no way to prove it. But the role of water in the future will be very important.

I'm a paleo-oceanographer, paleoclimatologist, and I also know a lot about how the ocean works today. Looking at the paleoclimate record, there are two things we can say for absolutely sure. One is that the Earth's climate has undergone global changes that are really big and abrupt. The temperature in Greenland probably changed by as much as 10 degrees in a very short time -- maybe two decades. Huge changes! We now have evidence these changes were synchronous in the equatorial tropics and the South Temperate region in the Southern Hemisphere. The only place they didn't happen is across the Antarctic convergence. There, it's like another planet anyway.

You cannot explain these abrupt changes by using rising sea levels, ice volume, or CO2; they all change too slowly. You could try to use the sun, but it would have to be a mega-solar event, and there's no evidence for it. So we look for an internal mechanism that must produce very rapid changes, and changes broadly symmetrical about the Equator. So logically, it's something driven from the Equator. And the great upwelling plumes of air along the inner Tropical Convergence along the Equator carry a fair amount of the world's moisture into the air.

In fact, a students and I want to work on a model to find out where the water comes from. We can color the water in temperature strips, look at the vapor and say how much of it over Chicago comes from the tropical ocean, from the Gulf of Mexico. This doesn't mean it's right, but it's better than your intuition. Somehow the inventory of water vapor in the air must be changed a lot to make these coolings of 20 to 30 percent lower than now.

How did water vapor do that? Most atmospheric physicists agree you can't change the amount of evaporation because it's driven mainly by sunlight, and there wasn't any change in sunlight. The amount of water molecules leaving the ocean surface for the air probably never changed that much. Cross it off the list. You've only got one way left: to have water molecules stay in the air a shorter period of time. Now the average residence time of water vapor in the air is two days to two weeks. Those water molecules are rained out pretty rapidly.

So the next question becomes: how could you change the residence time, say, have water molecules that come out of the ocean stay in the air on average a 20 to 30 percent shorter time than now? Well, in the great tropical convective plumes a lot of water that goes up, rains out; air rises and cools and expands and rains. It's been suggested that maybe if the dynamics were somewhat variable, it might rain out a greater fraction. More water might be squeezed out and not escape above or out the sides or wherever it goes. Then you'd cut down the delivery of water into the tropical atmosphere. This would cut down the inventory for the rest of the world.

One of my arguments for a cooling planet from lesser water vapor comes from the fact we had a cooler tropics by 5 percent. Also there's no other mechanism than changing water vapor content of the air. If you cool the planet, you automatically lower the water vapor in the air. It's the inverse of warming the planet. But you've got to have some reason for doing it. I say, the chicken is the water vapor. And the egg is the cooling. So we must find out how you dry out the air. We know the isotopic composition of ices from snow that fell in the Andes during the Glacial Period was depleted in Oxygen-18 in a way consistent with a drier air.

Q: So how do the oceans' great conveyor belts fit into a water vapor model of climate change?

WB: I say there's only one part of the Earth's system having bimodal or multiple states. That's the deep ocean circulation. There maybe others, but no one's found them. Well in a model, if you just turn on and off the conveyor, the climate changes are confined to the same latitude belts. They pick up at the Western Boundary of the Atlantic and penetrate deeply into the Eastern Boundary because of the prevailing winds. They don't show up in California, Japan, and certainly not in New Zealand. There's got to be a link between the Atlantic circulation and other things. What is that link?

When you change the deep circulation, you probably change many things. There must be changes in other places associated with this. Now we have evidence that indeed there have been. Bell and Kenneth at [UC] Santa Barbara have found one of the Greenland Events in the Santa Barbara Basin deep sea core record. It shows huge changes with temperature and carbon cycling. This tells us during that cold event something happened to the circulation --a tremendous ventilation in the upper ocean of the North Pacific that isn't happening now.

Okay, we've gotten one step further and said somehow the upper ocean circulation also underwent major changes right in tune with Greenland. It can't be simple heat release because the North Pacific wouldn't know about that. So how do we link it to the Equator? A major part of the Equatorial heat budget is upwelling cold water. The temperature of the surface ocean is cold at the Poles, and gets warmer and warmer until you get near the Equator, where it gets colder again. Because the cold water that's upwelling along the Equator is fed by the upper ocean. Water that has moved north into the temperate regions, 40 degrees latitude or so, sinks into the thermocline, then rises again up under the Equator.

If you made a major change in this circulation, you probably make a change in this upwelling plumes pattern and hence the delivery of water vapor to the atmosphere, and in turn the inventory of water vapor. Hypothetically, our planet is capable of snapping from one climate state to another because it's all linked together -- between the Atlantic and Upper Pacific, from Tropical upwelling to Tropical atmosphere!

In a circulation model of the atmosphere I'd like to put in parameters determining how much of the water vapor leaving the ocean comes back as rain. I'd want to tune up the rain and tune down the reevaporation, and see how much you can lower the water vapor content. See whether the mechanism has the punch to do the job. Certainly using inadequate models is better than just speculating in your mind.

Next: Playing Russian Roulette With the Climate

Sent By:Kathleen Stein on Friday, January 31, 1997 at 11:22:54.

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