You can be quite confident that as we use the fossil fuels, nature will produce more, and that this new natural production will be grossly inadequate to help us over the next decades to centuries.
Let's go back to the Where Is the Carbon diagram, which is repeated for your convenience. You’ll see that it shows 0.2 Gt C per year going into “surface sediment” at the bottom of the ocean. Other estimates vary somewhat; one well-known textbook used 0.05 Gt C for this flux. With the figure showing a burn rate of 6.4 Gt C per year, a number that has risen close to 9 Gt C per year, 0.2 is not especially big, but it isn’t completely zero, either. But, you’ll also notice a return flux labeled “weathering” that is also 0.2 Gt C per year. In the natural setting, the amount of dead plants being buried, and the amount of fossil fuel seeping out or otherwise returning to the surface were very similar.
Video: Where is Carbon Going? (1:50)
Click here for a video transcript of "Where is Carbon Going?".
PRESENTER: So we're back at this figure from NOAA and from the IPCC, and the figure is showing us how much carbon is in places in billions of tons-- gigatons of carbon-- and how much carbon is moving between places in gigatons of carbon per year both for the natural situation-- either how much was there or how much was moving-- and for what humans have caused-- how much is there and how much is moving. You might ask the question-- if we burn all the fossil fuel or a lot of the fossil fuel, won't nature make more of it? And the answer is, well, yes, but not fast enough to matter.
And so you'll note that what we're burning now, in this figure, we are burning 6.4 gigatons of carbon per year. That number is now probably up around nine or even a little bit more. And nature does indeed bury carbon in sediments that can become fossil fuels, but you'll notice that the number down here is only 0.2. That's not very big compared to that nine we're burning up above.
And you'll also note that, in the natural system, that burial is offset by what they have labeled as "weathering" over here, which is about the same amount coming out. Nature will make more fossil fuels. Nature will not make more fossil fuels fast enough that it counts in human economies. You have to think of hundreds of thousands and millions and more years to make enough fossil fuels to matter.
NOTE: Please realize that while you saw this figure on the previous page, the video discussion here focuses on different aspects of this figure.
The black pre-industrial carbon values show the carbon cycle and the balance that existed without human emissions. The red values indicate the effects that the human emissions have had on the carbon cycle. Increased emissions have increased levels of carbon in the atmosphere, pressuring the ocean and land biosphere to accept more carbon and limiting their future effectiveness as carbon dioxide sinks.
The total amount of buried organic carbon, former dead plants, may be 10,000,000 Gt C, but that accumulated over 4.6 billion years, so the rate has averaged only 0.002 Gt C per year, tiny compared to our use. And, almost all of that buried organic carbon is too widely distributed to be used as fossil fuel; we would expend more energy getting it than it would yield when burned. The available resource is shown in the figure as 3500 Gt C, and other estimates are a little higher. Most of the resource accumulated in the last 500 million years, at a rate of roughly 0.00001 Gt C per year.
Thus, we are burning the fossil fuels roughly a million times faster than nature saved them for us. Nature will make more fossil fuels over geologic time, but what we burn is gone forever on the timescale of human economies. We have been given a “bank account” of fossil fuels, but when we spend it, it’s gone, with no significant deposits being made.