Video transcript
The video is 7 minutes and 39 seconds long.
Produced by the American Museum of Natural History, September 2004.
Visual: A young man in Central Park.
Speaker: A young man in Central Park
Have I ever heard of the NAO? No. Can’t say that I have.
Visual: A young woman in Central Park.
Speaker: A young woman in Central Park
NAO? No, I have no idea.
Visual: Two men in Central Park.
Speaker: A female interviewer
It actually stands for the North Atlantic Oscillation.
Speaker: One of the men.
A-hah.
Speaker: A female interviewer
Have you ever heard of that?
Speaker: One of the men.
No.
Visual: A young European couple in Central Park.
Speaker: The woman in the couple.
North Atlantic Association.
Speaker: The man in the couple.
Oscillation.
Speaker: The woman in the couple.
Oscillation.
Visual: A group of senior citizens on a bench in Central Park
Speaker: The women in the group, overlapping.
North Atlantic Oscillation?
Visual: Title: NAO: Driving Climate Across the North Atlantic
Speaker: The group of senior citizens
Oscillation? What’s oscillating? What is oscillating?
Visual: Jim Hurrell, Atmospheric Scientist, National Corporation for Atmospheric Research, in his office
Speaker: Jim Hurrell, Atmospheric Scientist, National Corporation for Atmospheric Research
Not many people have ever heard of the North Atlantic Oscillation, but they should because it is the primary driver of weather and climate variability over much of the Northern Hemisphere.
Visual: Montage of bikes passing on a beach, a canoe in a mountain stream, trekkers on an icy mountain face, a ship in a harbor, snow falling on trees, a man on a bike, children playing in the surf.
When we talk about forecasting the weather, we’re really talking about very short-term events in the atmosphere.
Visual: A river flowing underneath ice, green hills, a desert, a forested mountainside, the ocean,
When we talk about climate, we’re talking in some sense about the average weather―the details of how the ocean and the atmosphere and the land surface interact over a longer period of time, perhaps 20 or 30 years.
Visual: A map of the Atlantic Ocean
The North Atlantic Oscillation is defined by the difference in atmospheric pressure between low pressure over Iceland and high pressure over the Azore Islands. And when the pressure difference is greatest, the winds blowing from west to east across the Atlantic tend to be stronger. And this changes the distribution of temperature and precipitation from the United States through Europe and Asia.
Visual: Martin Visbeck, Research Scientists, Lamont-Doherty Earth Observatory, in office.
Speaker: Martin Visbeck
We have very well understood the basic pattern of the North Atlantic Oscillation. We have a pretty good idea about the mechanism.
Visual: Martin Visbeck at computer examining climate data.
What we don’t know yet is how to predict the North Atlantic Oscillation.
Visual: Exterior of building, reading “National Center for Atmospheric Research: Sponsored by the National Science Foundation.”
Visual: Jim Hurrell operating computer. A computer-generated image of Earth, with cloud data.
Speaker: Jim Hurrell
The only way that we can begin to answer questions about the future behavior of the climate system is by building models of the climate system.
Visual: A map of Earth, with sea surface temperature data. Jim Hurrell examines numerical data on his monitor.
A climate model is essentially a very large set of complex mathematical equations that describe the evolution of the atmosphere, of the ocean, of the land surface.
Visual: An aerial image of a shoreline. Various other computer images showing cloud and temperature data.
By solving this very complex set of equations the climate model can produce its own climate that mimics how the real world operates.
Visual: A computer image of Earth, overlaid with colored bands representing climate data.
Speaker: Martin Visbeck
So what we see here, is a snapshot of the climate condition in the North Atlantic sector. A lot of lines together mean there’s very strong winds following parallel to these lines from west to east.
Visual: Martin Visbeck traces isobar lines with pen on computer monitor.
What we study when we look at the North Atlantic Oscillation is how this picture changes over time. We see the temperatures in colors here. And you see the cold air from the Arctic goes towards Labrador, giving you very cold conditions in northern Canada and Greenland. That would be the positive phase of the North Atlantic Oscillation. And at other times, you see the cold air showing up over Europe. That’s the negative phase of the North Atlantic Oscillation. But you definitely notice that it never happens at the same time. Either Europe is warm, and it’s very cold over Labrador, or the other way around. And this seesaw in temperatures is associated with the North Atlantic Oscillation.
Visual: Montage of computer generated visualizations of climate data. The ship, Oleander.
Speaker: Jim Hurrell
It’s very important that we evaluate these models relative to reality. So we need observations of the real world.
Visual: Two men on the bridge of the Oleander.
Speaker: One of the men on the bridge.
Requesting clearance to transit the narrows, over.
Speaker: Radio garble
Visual: Montage of two men on the Oleander hauling bulky equipment, various places on board the ship, a researcher with a pistol-like recording device pointed at the water, other researchers hauling back from the water scientific apparatus.
The Oleander goes out into the North Atlantic Ocean, and it measures the temperature, the salinity, the phytoplankton distribution.
Visual: The researchers attend to the apparatus.
This gives us a body of observations from which we can actually evaluate our climate models.
Visual: Scott Prosise takes an instrument out of a cardboard box.
Speaker: Scott Prosise, Lead Forecaster, National Weather Service
This is called a deep blue. It’s a buoy that will measure the water temperature down to a depth of 750 meters.
Visual: Scott Prosise throws the bouy overboard, then points the pistol-like device at it in the water.
It will also continue the climatological data that the Oleander has been doing for many years in logging the ocean’s temperature.
Visual: Scott Prosisa brings the pistol-like device to a cabin on the Oleander, and examines its data on a computer monitor.
Speaker: Martin Visbeck
Visual: On the bridge of the Oleander, a crewmember examines charts.
From instruments we have about a hundred years of data. What we’d really like to have is a record, which is a thousand years long.
Visual: A license plate reading, “DRDENDRO”. A man opens the trunk of a car and takes out an instrument.
Now obviously we cannot go back and take barometric measurements a thousand years ago. So we have to use different tools.
Visual: Edward Cook walks through a forest.
Speaker: Edward Cook, Doherty Senior Scholar, Lamont-Doherty Earth Observatory
The tree ring research is so exciting because it’s sort of a new discovery around every corner.
Visual: Edward Cook standing on wooded hilltop.
Finding trees that are 300 or even 400 years of age is a remarkably useful discovery because we can now use the ring width variations to tell us about periods of past drought and wetness and such like that. Kind of like what we’re seeing right here with the rain.
Visual: Edward Cook prepares tree-coring device, and inserts it into the trunk of a tree.
We extract a five-millimeter diameter core of wood from the tree. It’s analogous to almost like a hypodermic needle for a human.
Visual: Edward Cook extracts tree core sample from tool.
This is what we will take home to the lab for analysis. I can very clearly see the annual banding that represents each year of growth of this trees life.
Visual: A television monitor shows the view of the tree core sample, as magnified by microscope.
A narrow ring would mean drier than normal, and a wide ring would mean wetter than normal.
Visual: Edward Cook examines the core sample through the microscope, and counts the rings in the core sample by hand, using a pencil.
And all this information can be utilized to reconstruct past climate of various kinds.
Visual: Montage of images of Earth as viewed from space.
Speaker: Jim Hurrell
One of the factors that has really caused there to be a resurgence of interest in the North Atlantic Oscillation is how will global warming interact with these dominant patterns of climate variability, such as the North Atlantic Oscillation?
Visual: Jim Hurrell in office
So one of the key things that we need to understand is how the North Atlantic Oscillation has varied through time.
Visual: A graph showing air pressure data over various winters.
And that’s what you see here in this pressure difference index, which shows how the oscillation has varied in time from about 1864 up until the most recent years. You can see that there are very large fluctuations from one year to the next, and it almost has a random appearance.
Visual: A superimposed line slants upward through the data Jim Hurrell points out with his hand.
But one of the ways in which that has changed in recent decades is you can see a strong upward trend in the index, from very low index values during the 1950’s and the 1960’s to now persistently highly positive values of the index in recent decades.
Visual: Montage of an urban highway, industrial smokestacks churning out smoke, cars on a highway, a city choked in air pollution.
That tells us that there’s something else that might be nudging the atmosphere into this positive state of the North Atlantic Oscillation. And I think that fairly clear evidence is emerging that the buildup of greenhouse gases in the atmosphere is warming up the tropical oceans.
Visual: People playing in the surf at the beach, a packed urban sidewalk.
And through our experiments with climate models we are now able to show that warmer tropical oceans have an impact on the North Atlantic Oscillation.
Speaker: Martin Visbeck
Visual: People in the city, and on the beach.
Everybody asks me, “Martin, what is the climate going to be in the next century? What is the weather going to be next week? What is the NAO going to do next year?”
Visual: Scientists in the laboratory, scientists aboard the Oleander.
Now this is a very difficult question, and what scientists are trying to do, is they’re trying to understand how climate works today, how it has worked in the past, and then, by our understanding of the climate system, extrapolate towards the future.