The most recent carbon cycle research was presented at the eighth edition of the International Carbon Dioxide Conference in Jena, Germany in September. Most of the talks were held in a plenary session, allowing the attendees to pick up as much information as possible. The communal atmosphere fostered discussion, feedback, and plans for future collaborations. What was learned from more than 500 posters and 100 talks could easily fill a comprehensive textbook on the carbon cycle. However, here we summarize some of the content of the meeting, which covered all aspects of the carbon cycle, including land and ocean sinks, atmospheric concentrations and transport, and fossil fuel emissions.
Oceans
Roughly half of the CO2 emitted by human activity each year remains in the atmosphere. The other half is split between the terrestrial biosphere and the oceans. Several talks focused on the oceanic sink for anthropogenic CO2. Andrew Watson, from the University of East Anglia, spoke about evidence for decadal changes in the oceanic carbon cycle, such as decreases in the anthropogenic CO2 at depth due to changes in deep water formation in the Labrador Sea from 1997 to 2003. These changes appear to be partially forced by anthropogenic climate change and partially by natural oscillations in oceanic circulation and the climate system. Such observations challenge the conventional assumption that the oceanic carbon cycle is in a steady state.
Land
Carbon scientists have been working to quantify the land carbon sink for more than a decade. Two talks focused on the roles of land use change and natural disturbances in the land sink. Richard Houghton, of the Woods Hole Research Center, estimated an annual flux of CO2 from land use change of 1.5 +/-0.7 petagrams of carbon (PgC). Conversion of forest to crops and pasture are the largest components of this flux. Depending on the dataset, tropical emissions from land use change in the 1990s was anywhere between 0.9 and 2.4 Pg C per year. Disturbances such as the pine beetle in the Canadian Rockies, fire and extreme drought result in disequilibrium in the strength of the land sink according to Yiqi Luo, from the University of Oklahoma. Quantifying these disturbances and understanding how climate change will affect them are essential tasks for quantifying the future land sink. Enhanced observational networks and experimental studies will be necessary for these to be achieved.
Anthropogenic CO2
Today we are at a point where science has proven that recent greenhouse gas increases in the atmosphere are due to humans. According to Pieter Tans, from at NOAA’s Climate Monitoring and Diagnostics Laboratory, we cannot afford to wait to take action. He cited a one-in-six chance that continental temperatures will rise by 20°F due to doubling CO2 [Roe and Baker, 2007]. “I think this is a chance we should not take,” he said. He claimed that the developing world carries the burden to reduce emissions, and “we need to demonstrate to developing countries that development is possible with very low emissions.” But what role will scientists play? Tans said that observations and atmospheric transport models can give assurance that emissions reductions are working. In doing this work, scientists must fully disclose their data and methods. He also recommended scientific assessment of proposed geoengineering solutions.
David Archer, from the University of Chicago, presented the long-term implications of not reducing fossil fuel emissions. Once emissions are cut, the amount of CO2 in the atmosphere will decrease over a period of several hundred years due to dissolution into the ocean. However, eventually the ocean’s ability to take up CO2 will be depleted, and CO2 will be removed from the atmosphere via reactions with calcium carbonate and silicate rocks. Once atmospheric CO2 and calcium carbonate reach equilibrium, approximately 10% of the carbon dioxide will remain in the atmosphere, Archer said. According to a study by Berner and Kothavala [2001], it could take 400,000 years before the last of the human-released CO2 is removed from the atmosphere. In other words, our actions today will impact climate on a geologic time scale. For example, Archer stated that emitting 5,000 gigatons of carbon would increase global mean temperature by 3°C for tens of thousands of years. Archer drove in his point of the long-term implications of fossil fuel emissions by saying, “It’s like somebody’s walking off a cliff. It will take them 10 seconds to hit the ground and you’re telling them the next 10 milliseconds won’t be all that painful.”
And some pictures of poster sessions and the dinner:
