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The Global Carbon Budget 2013

Vegetation and the atmosphere interacting

November 2013: The Global Carbon Project provides an annual update to the state of anthropogenic carbon dioxide emissions that have provided underpinning guidance to the latest IPCC AR5.

In their latest update the world's carbon budget for 2012 is presented. This year's report shows that atmospheric carbon dioxide levels increased in 2012 at a faster rate than the average over the past 10 years because of a combination of continuing growth in emissions and a decrease in land carbon sinks from very high levels in the previous two years. The report also reveals that total human emissions of CO2 since the pre-Industrial period are well over half way toward the IPCC estimated threshold for staying below 2°C warming relative to pre-industrial.

For the year 2012, fossil fuel emissions were 9.7 ±0.5 GtC yr-1, a 2.2% increase over 2011 (a gigaton is 1 billion tonnes). An additional 0.9 ±0.5 GtC yr-1 is estimated from land-use change. However, atmospheric carbon dioxide concentration in 2012 increased by only 5.2 ±0.2 GtC. The rest was absorbed by the oceans (2.9 ±0.5GtC) or the land (2.5 ±0.9 GtC).

The land and ocean typically absorb approximately half of anthropogenic emissions. Any change in the efficiency of these sinks will have significant consequences for accumulation of anthropogenic CO2 in the atmosphere.

Cumulative emissions from pre-industrial (1750-2012) have reached 590 ±75 GtC. This is an update to the IPCC 1750-2011 estimate of 555 [470 - 640] GtC as 2012 emissions are included and an upwards revision is made of early 20th century land use emissions (20 GtC). The IPCC estimates that with cumulative emissions of 1000 GtC, there is a two-thirds chance of staying below 2°C relative to pre-industrial. At current levels we are over half way towards this figure. If other non-CO2 gases are included the emissions budget reduces to 790 GtC.

Fossil fuel emissions are estimated to continue to increase to 9.9 GtC yr-1 in 2013.

Atmospheric CO2 increases above preindustrial levels first began through releases of carbon to the atmosphere from deforestation and other land use activities. Starting in the 1920s, combustion of fossil fuels became the dominant source of anthropogenic emissions. Anthropogenic emissions occur on top of the natural carbon cycle that circulates carbon between the atmosphere, ocean and terrestrial biosphere.

The Met Office Hadley Centre develops and uses complex Earth System Models incorporating representations of the ocean and terrestrial biosphere to inform policy on future emission pathways that are compatible with climate targets.

This study was led by Professor Corrine Le Quéré of the University of East Anglia. Met Office Hadley Centre Scientist Dr Andy Wiltshire and Dr Anna Harper of the University of Exeter contributed to the study. Andy Wiltshire leads the Terrestrial Carbon Cycle research group.

Cumulative emissions have been rounded to 5GtC.


Global Carbon Budget 2013, by C. Le Quéré, G. P. Peters, R. J. Andres, R. M. Andrew, T. Boden, P. Ciais, P. Friedlingstein, R. A. Houghton, G. Marland, R. Moriarty, S. Sitch, P. Tans, A. Arneth, A. Arvanitis, D. C. E. Bakker, L. Bopp, J. G. Canadell, L. P. Chini, S. C. Doney, A. Harper, I. Harris, J. I. House, A. K. Jain, S. D. Jones, E. Kato, R. F. Keeling, K. Klein Goldewijk, A. Körtzinger, C. Koven, N. Lefèvre, A. Omar, T. Ono, G.-H. Park, B. Pfeil, B. Poulter, M. R. Raupach, P. Regnier, C. Rödenbeck, S. Saito, J. Schwinger, J. Segschneider, B. D. Stocker, B. Tilbrook, S. van Heuven, N. Viovy, R. Wanninkhof, A. Wiltshire, S. Zaehle, 2013. Earth System Science Data Discussion.

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