Atmospheric Carbon Dioxide Accumulation Speeding Up

Recent concern about the impact of anthropogenic carbon dioxide emissions on global warming and climate change have highlighted the importance of understanding long-term trends in inputs and sinks of carbon dioxde.

A research paper published online last week in the Proceedings of the National Academy of Sciences provides new insight into the influence of human activities on atmospheric carbon dioxide levels. According to the authors, the recent rapid rate of increase in atmospheric carbon dioxide is being caused by a decrease in the efficacy of carbon "sinks" brought about through climate change, and an increase in both the amount of human activity that leads to carbon emissions, and the amount of carbon released by a given amount of human activity.

The authors of the paper utilized data about atmospheric carbon dioxide levels (from data based on ice core samples, as well as global averages based on direct measurements), carbon emissions from the consumption of fossil fuels, emissions cased by changes in land use, and the relationships between global economy and energy use as well as between energy use and carbon emissions. These data were collected from reports previously compiled by groups such as the Global Carbon Project (www.globalcarbonproject.com), the National Oceanic and Atmospheric Administration, and other government agencies. The researchers used the data to determine how the rate of carbon dioxide flux into and out of the atmosphere changed between the time periods of 1979-1999 and 2000-2006.

The researchers found that the rate of growth in atmospheric carbon dioxide for the period of 2000-2006 is much higher than it has been in recent decades, and rates are the highest they have been since the start of continuous monitoring programs in 1959, as well as being the highest rates of increase seen since the beginning of the industrial revolution in the mid-1800s. The researchers estimated that most of the increase in CO2 emissions (65% +/- 16%) was due to increased amount of human activity, while 17% +/- 6% was due to decreases in carbon efficiency of human activities.

A substantial part of the rate increase-18% +/- 15%-- was associated with decreased ability of areas of land and ocean to function as carbon "sinks." These carbon "sinks" are places where carbon, often locked away in organic matter, can be sequestered and kept from from re-entering the atmosphere. However, several large carbon sinks have been affected by climate change in recent years, and their ability to removed CO2 from the atmosphere has decreased; as a result, more anthropogenic carbon has remained in the atmosphere, accelerating the rate of CO2 accumulation. According to the authors, these phenomena "characterize a carbon cycle that is generating stronger-than-expected climate forcing sooner than expected."

References:

Josep G Canadell et al., "Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks." Abstract and PDF available at http://www.pnas.org/cgi/content/abstract/0702737104v1