Some researchers have suggested that the sinks have already started to clog up, reducing their ability to take up more CO2 (J. G. Canadell et al. Proc. Natl Acad. Sci. USA 104, 18866–18870; 2007). Others disagree.
Ashley Ballantyne, a biogeochemist at the University of Montana in Missoula, worked with White and others to examine records of emissions as well as CO2 measurements made around the globe. They found no signs of sinks slowing down (A. P. Ballantyne et al. Nature 488, 70–72; 2012). But it is difficult to be sure, says Inez Fung, a climate modeler at the University of California, Berkeley. “We don’t have adequate observing networks.” The largest global network, operated by the US National Oceanic and Atmospheric Administration, had to trim 12 stations in 2012 because of budget cuts.
Some of the most crucial areas, such as the tropics, are also the least monitored, although researchers are seeking to fill in the gaps. Scientists from Germany and Brazil are building a 300-meter tower to keep tabs on the Amazon (see Nature 467, 386–387; 2010). And Europe’s Integrated Carbon Observation System is setting up stations throughout the continent and at some marine sites to measure CO2 and other greenhouse gases.
Satellites, too, could monitor carbon sources and sinks. Two orbiters are already providing some data, and NASA plans to launch the much anticipated Orbiting Carbon Observatory-2 next year (see page 5). An earlier version of that satellite failed during its 2009 launch.
Even as new resources come online, however, researchers are struggling to keep the Mauna Loa station going. “The amount of money that I’m able to obtain for the program has diminished over time,” says Keeling, whose group monitors CO2 concentration at 13 sites around the world.
“It’s kind of silly that we chose to go all ostrich-like,” says White of the funding difficulties. “We don’t want to know how much CO2 is in the atmosphere, when we ought to be monitoring even more.”