Weakening carbon sinks

Some recent figures published in the American Proceedings of the National Academy of Sciences suggest that terrestrial and marine carbon sinks are losing their ability to absorb carbon. In 2000, oceans and plant growth collectively absorbed about 600 of every 1000kg of carbon dioxide released into the atmosphere. In 2006, that had fallen to 540kg. While there is some degree of annual variation in such figures, a persistent downward trend would necessitate even more aggressive cuts in global human emissions.

Atmospheric CO2 concentrations are now about 383ppm, and increasing by nearly 2ppm a year, in line with growth in annual emissions of about 3.3%. Total emissions in 2006 were about 9.9 gigatonnes, compared with 8.4 gigatonnes in 2000. Recall that those figures are just for carbon dioxide; other greenhouse gases, such as methane and nitrous oxide, also contribute to planetary warming.

If terrestrial and marine carbon sinks continue to suffer from a reduced capacity to absorb CO2, the total level of sustainable emissions for the planet may end up being even lower than the 5 gigatonnes that the Stern Review estimates the planet can handle.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

9 thoughts on “Weakening carbon sinks”

  1. Saturation of the Southern ocean CO2 sink

    A four-year study by scientists from the University of East Anglia (UEA), British Antarctic Survey (BAS) and the Max-Planck Institute for Biogeochemistry reveals that an increase in winds over the Southern Ocean, caused by greenhouse gases and ozone depletion, has led to a release of stored CO2 into the atmosphere and is preventing further absorption of the greenhouse gas.

  2. The legend of the black horse

    Summoned in a moment of holy despair, the devil, in the form of a big black steed, appeared to help raise a church that was long overdue in the troubled village of Trois-Pistoles.

    La legende du cheval noir

    L’eglise aux moult clochers, grace au diable erigee, reste la comme une eternelle priere pour les gens des Trois Pistoles mais aussi pour tous les heros de la mer qui vont a la mort comme nous allons au plaisir.

  3. Nature 450, 491-492 (22 November 2007) | doi:10.1038/450491a; Published online 21 November 2007

    Carbon cycle: Marine manipulations

    Kevin R. Arrigo

    The effect of increasing levels of atmospheric carbon dioxide on carbon uptake in and export from the upper ocean is one of the big questions in environmental science. But it can be tackled experimentally.

  4. Nature 450, 545-548 (22 November 2007) | doi:10.1038/nature06267; Received 16 June 2007; Accepted 17 September 2007; Published online 11 November 2007

    Enhanced biological carbon consumption in a high CO2 ocean

    The oceans have absorbed nearly half of the fossil-fuel carbon dioxide (CO2) emitted into the atmosphere since pre-industrial times, causing a measurable reduction in seawater pH and carbonate saturation. If CO2 emissions continue to rise at current rates, upper-ocean pH will decrease to levels lower than have existed for tens of millions of years and, critically, at a rate of change 100 times greater than at any time over this period3. Recent studies have shown effects of ocean acidification on a variety of marine life forms, in particular calcifying organisms. Consequences at the community to ecosystem level, in contrast, are largely unknown. Here we show that dissolved inorganic carbon consumption of a natural plankton community maintained in mesocosm enclosures at initial CO2 partial pressures of 350, 700 and 1,050 muatm increases with rising CO2. The community consumed up to 39% more dissolved inorganic carbon at increased CO2 partial pressures compared to present levels, whereas nutrient uptake remained the same. The stoichiometry of carbon to nitrogen drawdown increased from 6.0 at low CO2 to 8.0 at high CO2, thus exceeding the Redfield carbon:nitrogen ratio of 6.6 in today’s ocean. This excess carbon consumption was associated with higher loss of organic carbon from the upper layer of the stratified mesocosms. If applicable to the natural environment, the observed responses have implications for a variety of marine biological and biogeochemical processes, and underscore the importance of biologically driven feedbacks in the ocean to global change.

  5. Climate change
    What lies beneath

    Dec 3rd 2009
    From The Economist print edition
    The planet’s ability to absorb carbon dioxide is under investigation

    AS THE world gathers in Copenhagen over the coming weeks to discuss how much carbon dioxide people should be putting into the atmosphere, the Benguela Stream will be docking in the Windward Isles to bring bananas to Europe for Christmas, and doing her bit to help ascertain where a large part of that CO2 ends up. The world’s oceans and plants absorb about 60% of the CO2 emitted as a result of human activities, which has helped keep the extent of climate change in check over the past century or so. But exact figures are hard to come by. Estimates of just how much carbon ends up in plants, in soil and in the oceans are frustratingly sketchy.

    The oceans suck up CO2 because it is soluble in water. Plants suck it up because they photosynthesise. As CO2 becomes more available, other things being equal, they will photosynthesise more. And a warmer, more polluted, more disrupted world can encourage growth in other ways, too. But none of these things can go on indefinitely. At some point the oceans and plants will have had their fill.

    At that moment, the problems being addressed in Copenhagen will get worse. They will get worse still if the “land sink”, as researchers call the plants and soils, actually goes into reverse, adding to net emissions rather than reducing them as the respiration of microbes (which increases as temperatures rise) outstrips the photosynthesis of plants. Some think that a slowdown in the sucking up has already begun. The poverty of the data and the complexity of the problem make it hard to be sure.

  6. NASA Study Finds Tropical Forests’ Ability to Absorb Carbon Dioxide Is Waning

    A recent study led by scientists at NASA’s Jet Propulsion Laboratory in Southern California identified whether vegetated areas like forests and savannas around the world were carbon sources or sinks every year from 2000 to 2019. The research found that over the course of those two decades, living woody plants were responsible for more than 80% of the sources and sinks on land, with soil, leaf litter, and decaying organic matter making up the rest. But they also saw that vegetation retained a far smaller fraction of the carbon than the scientists originally thought.

    In addition, the researchers found that the total amount of carbon emitted and absorbed in the tropics was four times larger than in temperate regions and boreal areas (the northernmost forests) combined, but that the ability of tropical forests to absorb massive amounts of carbon has waned in recent years. The decline in this ability is because of large-scale deforestation, habitat degradation, and climate change effects, like more frequent droughts and fires. In fact, the study, published in Science Advances, showed that 90% of the carbon that forests around the world absorb from the atmosphere is offset by the amount of carbon released by such disturbances as deforestation and droughts.

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