Bristol University researchers Pru Foster, Pierre Friedlingstein, Jo House and Colin Prentice from the University’s QUEST programme, together with a world-wide team of experts report that over the past 50 years the average fraction of global CO₂ emissions that remained in the atmosphere each year was around 43% - the rest was absorbed by the Earth’s carbon sinks on land and in the oceans.

Dr Jo House adds: “During this time this fraction has likely increased from 40% to 45% suggesting a decrease in the efficiency of the natural sinks. The team brings new evidence that the sinks are responding to climate change and variability”.

The scientists report a 29% increase in global CO₂ emissions from fossil fuel between 2000 and 2008 (the latest year for which figures are available), and that in spite of the global economic downturn emissions increased by 2% during 2008.

The use of coal as a fuel has now surpassed oil and developing economies now emit more greenhouse gases than developed countries – with a quarter of their growth in emissions accounted for by increased trade with the West.

Lead author Prof Corinne Le Quéré of the University of East Anglia and the British Antarctic Survey said: “The only way to control climate change is through a drastic reduction in global CO₂ emissions. 

“The Earth’s carbon sinks are complex and there are some gaps in our understanding, particularly in our ability to link human-induced CO₂ emissions to atmospheric CO₂ concentrations on a year-to-year basis.  But, if we can reduce the uncertainty about the carbon sinks, our data could be used to verify the effectiveness of climate mitigations policies.”

The main findings of the study include:

• CO₂ emissions from the burning of fossil fuels increased by two per cent from 2007 to 2008, by 29 per cent between 2008 and 2000, and by 41 per cent between 2008 and 1990 – the reference year of the Kyoto Protocol.
• CO₂ emissions from the burning of fossil fuels have increased at an average annual rate of 3.4 per cent between 2000 and 2008, compared with one per cent per year in the 1990s.
• Emissions from land use change have remained almost constant since 2000, but now account for a significantly smaller proportion of total anthropogenic CO2 emissions (20 per cent in 2000 to 12 per cent in 2008).
• The fraction of total CO₂ emissions remaining in the atmosphere has likely increased from 40 to 45 per cent since 1959, models suggests this is due to the response of the natural CO₂ sinks to climate change and variability.
• Emissions from coal are now the dominant fossil fuel emission source, surpassing 40 years of oil emission dominance.
• The financial crisis had a small but discernable impact on emissions growth in 2008 – with a two per cent increase compared with an average 3.6 per cent over the previous seven years. On the basis of projected changes in GDP, emissions for 2009 are expected to fall to their 2007 levels, before increasing again in 2010.
• Emissions from emerging economies such as China and India have more than doubled since 1990 and developing countries now emit more greenhouse gases than developed countries.
• A quarter of the growth in CO₂ emissions in developing countries can be accounted for by an increase in international trade of goods and services.

The researchers called for more work to be done to improve our understanding of the land and ocean CO₂ sinks, so that global action to control climate change can be independently monitored. The sinks have a major influence on climate change and are important in understanding the link between anthropogenic CO₂ emissions and atmospheric CO₂ concentration. But so far scientists have not been able to calculate the CO₂ uptake of the sinks with sufficient accuracy to explain all the annual changes in atmospheric CO₂ concentration, which hinders the scientists’ ability to monitor the effectiveness of CO₂ mitigations policies.