|Perturbation of the global carbon budget, 1959-2006. Click to enlarge. Source: Global Carbon Project.|
An international team of scientists has found that the annual rate of increase of the concentration of atmospheric CO2 has accelerated since 2000 to an average 1.93 ppm per year—an average annual rate 28% higher than that of the 1990s.
Lead author of the study and Executive Director of the Global Carbon Project, CSIRO’s Dr Pep Canadell, says that the acceleration is due to three factors: global economic growth; the world’s economy becoming more carbon intense (that is, since 2000 more carbon is being emitted to produce each dollar of global wealth); and a deterioration in the land and oceans’ ability to absorb carbon from the atmosphere at the required rate.
Between 2000 to 2006, human activities such as burning fossil fuels, manufacturing cement, and tropical deforestation contributed a net average of 4.1 billion metric tons of carbon to the atmosphere each year, yielding an annual growth rate for atmospheric carbon dioxide of 1.93 parts per million (ppm)—the highest since the beginning of continuous monitoring in 1959, according to the report.
By contrast, the growth rate in the 1970s was 1.3 ppm y-1; in the 1980s, 1.6 ppm y-1; and in the 1990s, 1.5 ppm y-1. The present atmospheric concentration of carbon dioxide is 381 ppm, 35% above pre-industrial levels, the highest concentration in the last 650,000 years, and probably in the last 20 million years.
The study attributed 65% of the current acceleration to increased activity of the global economy. The study found that deterioration of the carbon intensity of the global economy—i.e., the increasing inefficiency in the use of fossil fuels—accounted for another 17% of the increase, while the other 18% came from the decline in the efficiency of natural land and ocean sinks which soak up CO2 from the atmosphere.
While the worldwide acceleration in carbon dioxide emissions had been previously noted, this new study highlights the role of the weakening of land and oceans sinks. For example, the Southern Ocean winds have increased in response to greenhouse gases and ozone depletion. The increase in winds has led to a release of natural CO2 stored in the deep ocean, which is preventing further absorption of the greenhouse gas. (Earlier post.)
In addition to the study showing the decline in the uptake in the Southern Ocean, new research indicates that uptake in the North Atlantic has halved over the last decade. (Earlier post.) On land, where plant growth is the major mechanism for drawing carbon dioxide out of the atmosphere, large droughts have reduced the uptake of carbon.
Emissions from the burning of fossil fuels constituted the largest source of anthropogenic carbon, releasing an average of 7.6 billion metric tons each year between 2000 and 2006, a significant jump from 6.5 billion tons in the 1990s. Emissions generated by land-use changes such as deforestation have remained constant, but shifted in geographic focus.
The study also shows that the carbon intensity of the global economy (kilograms of carbon per dollar of economic activity) has increased since 2000 at about 0.3% per year, reversing a 30-year decline of about 1.3% per year. Because practically all proposed scenarios for managing future emissions postulate improvements in carbon intensity in the global economy, this deterioration of carbon intensity presents a serious challenge in stabilizing atmospheric carbon dioxide and mitigating climate change.
The research by the Global Carbon Project, the University of East Anglia (UEA) and the British Antarctic Survey (BAS) is published this week in the journal Proceedings of the National Academy of Sciences (PNAS).
What we are seeing is a decrease in the planet’s ability to absorb carbon emissions due to human activity. Fifty years ago, for every tonne of CO2 emitted, 600kg were removed by land and ocean sinks. However, in 2006, only 550kg were removed per tonne and that amount is falling.—Dr. Pep Canadell
The researchers for the study are Josep G. Canadell, CSIRO Marine and Atmospheric Research, Canberra, Australia; Corinne Le Quéré, University of East Anglia, School of Environment Sciences, Norwich, UK, and British Antarctic Survey, Cambridge, UK; Michael R. Raupach, CSIRO Marine and Atmospheric Research, Canberra, Australia; Christopher B. Field, Carnegie Institution of Washington, Department of Global Ecology, Stanford, CA; Erik T. Buitehuis, University of East Anglia, School of Environment Sciences, Norwich, UK; Philippe Ciais, Commissariat a L’Energie Atomique, Laboratorie des Sciences du Climat et de l’Environnement, France; Thomas J. Conway, NOAA Earth System Research Laboratory, Boulder, CO; Nathan P. Gillett, University of East Anglia, School of Environment Sciences, Norwich,UK; R. A. Houghton, Woods Hole Research Center, Falmouth, MA; Gregg Marland, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN, and International Institute for Applied Systems Analysis, Laxenburg, Austria.
Josep G. Canadell, Corinne Le Quere, Michael R. Raupach, Christopher B. Field, Erik T. Buitenhuis, Philippe Ciais, Thomas J. Conway, Nathan P. Gillett, R. A. Houghton, and Gregg Marland. “Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks” Proceedings of the National Academy of Sciences , October 2007.