They can measure how much CO2 is
invading the oceans by a variety of different techniques.
You can just go out and measure the concentration of CO2 and,
of course, there's a lot of dissolved carbon already in the water.
It's a tricky question to distinguish the tiny
fraction that is new carbon, that invaded the ocean from fossil
fuel combustion, but it can be done.
Or there is a very clever method that I wanted to show you that involves measuring
simultaneously changes in atmospheric CO2 and also oxygen.
When you burn fossil fuel, that's like respiration, it consumes oxygen
and so the CO2 concentration goes up and the oxygen concentration goes down.
Then there are two different possible fates
of that CO2 that we're trying to distinguish here.
One is that it could get taken up by trees on land
by some photosynthesis. When that happens it releases oxygen.
The other possibility is that it can just dissolve
in water and then it does this buffer chemistry, but
it doesn't immediately get turned into photosynthesis. It doesn't produce oxygen.
If you compare the rate at which CO2 is
rising with the rate at which oxygen is falling you can
decide how much of the carbon is going
into the land biosphere, verses how much is into the ocean.
The bottom line is about
50:50 (equal proportions).
There's about two gigatons a year going into the oceans.
And they can measure that by multiple methods and
they get the same answer by the different methods.
We have confidence in that.
And then, just by difference by balancing the budget, there has to be
an uptake going into the land of about three gigatons a year of carbon.
And this is dicier because we don't know where that is.
We're still trying to figure out even though it's a massive
amount of stuff but it's just harder to find on land.
Anyway the bottom line is that to a large extent the ocean
and the land are helping us out by absorbing fossil fuel CO2.