Just listened to this podcast this morning while walking to the shuttle to ride to work. There's a link to the transcript below. The theme of the story is that the existing ecosystem, forests especially, has captured a tremendous amount of carbon and could be (or is) induced to release that carbon quickly. The quick release of carbon from e.g. forest fires c/would swamp the emissions from direct human activity. He presents evidence that while the direct source is from existing vegetation, that the indirect cause is human activity causing an increase in atmospheric carbon (and other greenhouse gasses) that's causing an increase in temperature that is creating the conditions which are expected to cause the rapid release of carbon from the existing vegetation.
He several times contrasted the coverage of the forest fires in southern California last summer with the lack of coverage of even more massive forest fires in remote areas of northern Canada and remote areas of China. It seems the only time forest fires are covered is when they are a direct threat to human well-being, and the coverage focuses more on people losing their houses than the side effect. The side effect is that when the tree burns it releases its carbon. The carbon sequestered in the growth of that tree unsequesters and becomes part of the carbon increase that's supposedly causing global warming.
He discussed how forest fires are a natural part of the life of forests, especially the pine forests of the West and of Northern Canada. Some of the trees can only sprout new seedlings when there is a fire. However the issue is a matter of balance. There is more carbon being released through forest fires than is being absorbed by growth of new forest. And overall the whole ecosystem is seeing an over-abundance of carbon a large portion of which is directly from human activity.
There are lots of details, it is an information packed hour of listening.