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The human impact on the earth's carbon 
cycle is to dig up 

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some of the carbon in the solid earth reservoir 
and put it in the atmosphere, 

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00:00:21,654 --> 00:00:26,456 
a rate of about 8 gigatons per year. 
And also, we are 

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cutting down trees on land, which results 
in a flux 

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00:00:31,673 --> 00:00:37,548 
of CO2 to the atmosphere of about another 
2 gigatons a year

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The amount of 
CO2 in the atmosphere is going up. 

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But it's actually not going up as quickly 
as it 

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should be, given how much carbon we're 
putting into it. 

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

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There's a whole bunch of carbon that 
we're 

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putting in the atmosphere, which is not 
showing up. 

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

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The time scale for 
solid earth

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to take up carbon is very 
long. 

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That's not really helping us that much, 
presumably. 

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It's hard to measure how much carbon

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is going in to the land, because the 
land is so heterogeneous. 

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00:01:18,380 --> 00:01:21,308 
One tract of forest is very different from 
another. 

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And to know exactly how much carbon is 
being 

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absorbed, is a very difficult 
measurement to make. 

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Actually, interestingly they can measure 
the carbon uptake 

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in the ocean much more easily, much more 
precisely. 

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In the early days of thinking about 
this, back in the 

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1950s and before, people basically figured 
that the ocean would control the 

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

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atmospheric CO2, because the ocean, after 
all, has 70% of the earth's surface. 

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And it's also got a lot more carbon than 
the atmosphere does. 

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

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

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

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00:02:15,270 --> 00:02:19,090 
the way it moves from the surface where it 
can see the atmosphere 

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00:02:19,090 --> 00:02:22,580 
down into the deep which is where most of 
the ocean water is. 

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The way the ocean circulates is 

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that in the high latitudes, in Antarctica 
and in the 

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00:02:28,530 --> 00:02:32,100 
North Atlantic, where it gets very cold, 
the water at 

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00:02:32,100 --> 00:02:35,070 
the surface gets cold enough that it can 
sink

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00:02:35,070 --> 00:02:38,160 
by the same convection process we 
were talking about before,

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

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00:02:41,330 --> 00:02:47,450 
And so you have this very focused downward 
flow in very specific locations. 

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And this is balanced by 
vague and diffuse

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00:02:50,390 --> 00:02:56,250 
upward velocities every place 
else, or other parts of the ocean. 

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00:02:56,250 --> 00:03:00,665 
The overall time scale for the circulation 
of the ocean is about a 1000 years. 

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00:03:00,665 --> 00:03:03,629 
And that actually limits how quickly the 
CO2 

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can equilibrate between the atmosphere and 
the ocean.