Does all the carbon dioxide released by human activity add to the atmospheric concentration?

No. Careful measurements show that only a little over half of the carbon dioxide released by humans each year is staying in the atmosphere. Most of the rest is being dissolved into the oceans or taken up by plants and soil on land. This is actually very important, for at least three reasons:

• First, as we’ll discuss later, the carbon dioxide that dissolves in the oceans is making ocean water slightly more acidic, which creates the problem of “ocean acidification.”
• Second, this points to at least one potential way in which we can reduce the impact of our emissions: by planting trees or otherwise finding ways to get plants and soil to absorb more carbon dioxide.
• Third and more ominously, it also points to a potential future danger: If temperatures continue to warm, the oceans will gradually be able to dissolve less carbon dioxide, and eventually will start releasing some of the carbon dioxide they’ve already dissolved. This could therefore cause a further increase in the rate at which the carbon dioxide concentration rises in Earth’s atmosphere.