How long does carbon dioxide emitted by human beings remain in the atmosphere? It turns out, it is a tricky question. Different mechanisms remove carbon at different rates, and the responses of each system to higher concentrations of carbon dioxide in the atmosphere differ.
Probably the most important distinction is between sinks that have a capacity that can be exhausted and those that are effectively limitless. Oceans the biosphere are of the first kind, and they respond to carbon dioxide in the atmosphere relatively quickly. That being said, there is a limit to how much carbon dioxide the ocean can absorb (and the fact that it becomes more acidic while doing so is problematic) and there is only so much biomass the planet can sustain. Weathering rock that absorbs carbon and then subducts below the seafloor is an example of the second type of sink: though it operates very slowly and volcanic eruptions can return carbon that has been locked into the lithosphere back to the atmosphere. Even without such eruptions to worry about, natural weathering is not the route to a stable climate on a human timescale. As the Nature article linked above explains: “it would take hundreds of thousands of years for these processes to bring CO2 levels back to pre-industrial values.”
The article also comments on how long the temperature anomaly from anthropogenic emissions will persist: “whether we emit a lot or a little bit of CO2, temperatures will quickly rise and plateau, dropping by only about 1Â°C over 12,000 years.” We should make no mistake in understanding that our choices about how much carbon dioxide we emit will have a big impact on a huge number of future generations.