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Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution
among the atmosphere, ocean, and terrestrial biosphere is important to better
understand the global carbon cycle, support the climate policy process, and project
5 future climate change. Present-day analysis requires the combination of a range of
data, algorithms, statistics and model estimates and their interpretation by a broad scientific
community. Here we describe datasets and a methodology developed by the
global carbon cycle science community to quantify all major components of the global
carbon budget, including their uncertainties. We discuss changes compared to pre10
vious estimates, consistency within and among components, and methodology and
data limitations. Based on energy statistics, we estimate that the global emissions
of CO2 from fossil fuel combustion and cement production were 9.5±0.5 PgC yr−1
in 2011, 3.0 percent above 2010 levels. We project these emissions will increase
by 2.6% (1.9–3.5 %) in 2012 based on projections of Gross World Product and re15
cent changes in the carbon intensity of the economy. Global net CO2 emissions from
Land-Use Change, including deforestation, are more difficult to update annually because
of data availability, but combined evidence from land cover change data, fire
activity in regions undergoing deforestation and models suggests those net emissions
were 0.9±0.5 PgC yr−1 in 2011. The global atmospheric CO2 concentration is mea20
sured directly and reached 391.38±0.13 ppm at the end of year 2011, increasing
1.70±0.09 ppm yr−1 or 3.6±0.2 PgC yr−1 in 2011. Estimates from four ocean models
suggest that the ocean CO2 sink was 2.6±0.5 PgC yr−1 in 2011, implying a global
residual terrestrial CO2 sink of 4.1±0.9 PgC yr−1. All uncertainties are reported as ±1
sigma (68% confidence assuming Gaussian error distributions that the real value lies
25 within the given interval), reflecting the current capacity to characterise the annual estimates
of each component of the global carbon budget. This paper is intended to
provide a baseline to keep track of annual carbon budgets in the future.
