Caroline Alden, BURN Contributor

A recent BURN Journal post on the global carbon cycle and the fate of fossil fuel CO2 emissions – Carbon Cycle 101 – discussed how land plants and the world’s oceans slurp about half of fossil fuel CO2 emissions out of the atmosphere each year.

In other words, 50% of fossil fuel CO2 emissions are naturally sequestered by nature in land plants and ocean waters. The important corollary is that only half of the CO2 we emit each year remains in the atmosphere to trap heat and warm the globe.

Scientists have been waiting worriedly for these sinks to “saturate,” or quit taking so much extra CO2 out of the atmosphere. Models predict that land plants will soon become satisfied with the level of fertilization that extra atmospheric CO2 provides, and that ocean chemistry will soon lose its capacity to accommodate extra CO2.

A paper published last summer in Nature by researchers in Boulder, Colorado compared the growth rate of the concentration of CO2 in the atmosphere each year with the amount of CO2 put in the atmosphere by fossil fuel combustion each year since 1959.

What they found was that not only are land and ocean sinks still taking up excess CO2 from the atmosphere, but that the rate of uptake has grown steadily stronger for the last 5 decades!

sinks for caroline

Panel a shows the annual growth rate of CO2 in the atmosphere. Panel b shows emissions from fossil fuel combustion (in red) as well as land-use changes (gold). Panel c shows the difference between panels a and b, or the annual global net uptake of carbon by land and ocean sinks. The dark shaded areas represent 1-sigma uncertainties, and the light shaded areas represent 2-sigma uncertainties. (Source: Ballantyne and others, published in the journal Nature in August 2012)

This finding is both good news and bad news.

The good news is that, to date, climate change has probably been attenuated by strong natural sinks; if more of our emissions had remained in the atmosphere, the globe would have warmed more than it already has.

The bad news is that climate change is already happening, in spite of the 50% climate discount on emissions that the Earth’s natural sinks currently offer us.

That is troubling. What happens when natural sinks stop and that discount disappears?

Furthermore, these natural carbon sinks – the land sink in particular – are not permanent storage places for COand are vulnerable to extreme weather events and to climate change itself. Droughts and fires can release land carbon stores back to the atmosphere within a season.

When the land and ocean sinks saturate – and all signs say they very will soon – the impacts of each watt of electricity produced by a coal-fired power plant, of each mile driven by a gasoline-powered vehicle, and of each lawn mower lap around the back yard will be felt in full by greenhouse gas warming of the planet.

Caroline Alden is a graduate student at the Institute of Arctic and Alpine Research in the Department of Geology at the University of Colorado at Boulder.