Where Our Carbon Is Going

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From the course by The University of Chicago

Global Warming I: The Science and Modeling of Climate Change

157 ratings

The University of Chicago

Global Warming I: The Science and Modeling of Climate Change

157 ratings

This class describes the science of global warming and the forecast for humans’ impact on Earth’s climate. Intended for an audience without much scientific background but a healthy sense of curiosity, the class brings together insights and perspectives from physics, chemistry, biology, earth and atmospheric sciences, and even some economics—all based on a foundation of simple mathematics (algebra).

From the lesson

The Perturbed Carbon Cycle

On the carbon locked up in fossil fuels and what happens when we burn those fuels. In Part II of this class, you can create a simple but somewhat realistic model of Earth's temperature evolution in the coming decades, in response to the release of CO2 (or in the sudden stop of emissions in a scenario called "The world without us").

Where Our Carbon Is Going3:12

Ocean Buffer Chemistry6:14

The Perturbed Carbon Cycle2:42

Methane as a Greenhouse Gas8:49

The Long CO₂ Tail5:37

Why the CO₂ Tail Matters6:35

Meet the Instructors

David Archer
Professor
Geophysical Sciences

[MUSIC]

So the human impact on the Earth's carbon cycle is to dig up some

of the carbon in the solid earth reservoir and

put it in the atmosphere at a rate of about eight gigatons per year.

And also, we're cutting down trees on land, which results in a flux of CO2

to the atmosphere of about another two gigatons a year.

Now, the concentration of the amount of CO2 in the atmosphere is going up, but

it's actually not going up as quickly as it should be,

given how much carbon we're putting into it.

It's only going up at about four or five gigatons per year.

So there's a whole bunch of carbon that we're putting in the atmosphere

which is not showing up.

It's going away into some combination of the land the ocean.

We know just the time scale for solid earth to take up carbon is very,

very long.

So that's not really helping us that much presumably.

It's hard to measure how much is going into the land, because the land is so

heterogeneous, one tract of forest is very different from another and

to know exactly how much carbon is being absorbed is a very difficult

measurement to make actually.

Interestingly, they can measure the carbon uptake in the ocean much more easily,

much more precisely.

[SOUND] So in the early days of thinking about this back in the 1950s and

before, people basically figured that the ocean would control the atmospheric

CO2 concentration and that we wouldn't really be able to change atmospheric CO2,

because the ocean after all has 70% of the earth's surface.

And that it also got a lot more carbon than the atmosphere does,

about 40 times more, and so it's a really heavy hitter in the carbon cycle.

The reason why the ocean doesn't just immediately mop up all of our extra CO2

has to do mostly with the fact that the way that the ocean water circulates,

the way it moves from the surface where I can see the atmosphere down into the deep,

which is where most of the ocean water is.

The way the ocean circulates is that in the high latitudes in Antarctica and

in the north Atlantic where it gets very cold, the water at the surface gets cold

enough that it can sink by the same sort of convection process we were talking

about before, but now upside down because we're cooling it from above.

And so, you have this very focus downward flow in very

specific locations and this is balance by very, by sort of vague and

diffuse upward velocities every place else or other parts of the ocean.

The overall time scale for the circulation of the ocean is about a thousand years.

And that actually limits how quickly the CO2 can

equilibrate between the atmosphere and the ocean.

[MUSIC]

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