The Global Carbon Budget 2014
September 2014 - 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 assessment.
Their latest update presents the world's carbon budget for 2013. This year's report shows that atmospheric carbon dioxide levels increased in 2013 at a faster rate than the average over the past 10 years because of a combination of continuing growth in emissions and a change in the land and ocean carbon sinks. 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 2013, fossil fuel emissions were 9.9 ±0.5 Gigatonnes of carbon (GtC), a 2.3% increase over 2012 (a gigatonne is 1 billion tonnes). An additional 0.9 ±0.5 GtC is estimated from land-use change. However, atmospheric carbon dioxide concentration in 2013 increased by only 5.4 ±0.2 GtC to 395 ppm. 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 (1750-20134) have reached 580 ±75 GtC. This is an update to the IPCC 1750-2011 estimate of 555 [470 - 640] GtC to include 2012-2013 emissions and a revision of early 20th century land use emissions. The IPCC estimates that with cumulative emissions of 1000 GtC, there is a two-thirds chance of staying below 2°C warming relative to pre-industrial temperatures. Keeping warming below two degrees requires total CO2 emissions to remain below this target. At current levels we are over half way towards this figure. If other non-CO2 gases are included, the emissions budget is substantially reduced.
Fossil fuel emissions are estimated to continue to increase to 10.1 GtC yr-1 in 2014. At the current emission rate the remaining 2 degree carbon budget will be used by 2045. An additional emissions above this ceiling will substantially reduce the chance of staying below the 2 degree target. To increase this budget negative emission technology will be required. One such example is Bio-Energy Carbon Capture and Storage (BECCS). In this technology crops are grown for fuel and the carbon captured during combustion. BECCS can therefore offset both demand for fossil fuels as a clean energy technology, as well removing carbon from the atmosphere. However, credibility of BECCS as a climate change mitigation option is unproven and substantial challenges remain, particularly the sustainability of production given existing issues around food security.
Atmospheric CO2 increases above pre-industrial 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 that incorporate representations of the ocean and terrestrial biosphere to inform policy on future emission pathways that are compatible with climate targets. This includes ongoing research into the role of negative emission technologies in carbon budgets.
The global carbon project is an international programme led by Professor Corrine Le Quéré of the University of East Anglia. This year's budget includes not only the 2013 emission information but additional research into carbon budgets consistent with climate targets. Met Office Hadley Centre Scientists Chris Jones and Dr Andy Wiltshire contributed to the study. Chris Jones is head of Earth System and Mitigation Science and Andy Wiltshire leads the Terrestrial Carbon Cycle research group.
The data from the Global Carbon Project can be explored and visualised at the Global Carbon Atlas.
Cumulative emissions have been rounded to 5GtC.
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