Growth in carbon emissions accelerating; exceeding worst case scenario

An international team of scientists has taken another look at how rapidly Earth's atmosphere is absorbing carbon dioxide (CO2) - the biggest greenhouse gas in terms of volume - and the news is not good: a high-flying world economy is pumping out the gas at an unprecedented rate while natural carbon sinks such as oceans and terrestrial ecosystems have become less efficient in sequestering carbon. Because of this, current atmospheric CO2 levels are outstripping the best estimates used by modelers to predict future climate trends. The team reports its findings in an open access article in the Proceedings of the National Academy of Sciences USA.

The growth of carbon emissions from fossil fuels has tripled compared to the 1990s and is now exceeding the predictions of the highest IPCC emission scenarios - the problematic A1FI scenario, based on very rapid, fossil intensive economic growth (graph, click to enlarge). Key data from the report:

• Atmospheric CO2 has grown at 1.9 parts per million (ppm) per year compared to about 1.5 ppm during the previous 30 years
• The growth in emissions from fossil fuels increased from 1.3% per year for 1990-1999 to 3.3% per year during the period running from 2000 to 2006; total carbon emissions now stand at 9.9 Petagram per year, of which 8.4 comes from fossil fuels and 1.5 Pg from land-use changes (graph, click to enlarge)
• Emissions generated by land-use changes have remained constant, but have shifted in geographic focus (from South America, where a decline in deforestation has occured, to South and South East Asia)
  
• The efficiency of natural carbon sinks - oceans and terrestrial plant growth - has decreased by 10% over the last 50 years and will continue to do so in the future, implying that the longer we wait to reduce emissions, the larger the cuts needed to stabilize atmospheric CO2. A number of large droughts in the mid-latitudes (Europe, North America, Central asia) has reduced the capacity of plants to sequester carbon in these regions (map, click to enlarge)
  
• For the first time in 100 years, the carbon intensity of the world’s economy has stopped decreasing; since 2000, carbon output per dollar of productivity has been increasing by 0.3% per year, whereas during the previous 3 decades, it was dropping by an average of 1.3% per year (graph, click to enlarge)
• All of these changes characterize a carbon cycle that is generating stronger climate forcing and sooner than expected

The share of the different drivers of the increased atmospheric CO2 levels is as follows:

• 65% due to the increased activity of the global economy
• 17% due to the deterioration of the carbon intensity of the global economy
• 18% due to the decreased efficiency of natural sinks

When it comes to regional contributions, the trend is straightforward: all economies have increased their carbon emissions. The largest growth can be seen in China and India, two countries whose economies are growing very rapidly; the developing world's contribution (D1, D2, D3) is inreasing significantly, whereas that of the Former Soviet Union is beginning to pick up again after the decline resulting from the economic collapse during the 1990s. Only the EU seems to have succeeded in more or less stabilising its carbon emissions (graph, click to enlarge).

Between 2000 to 2006, human activities such as burning fossil fuels, manufacturing cement, and land-use changes contributed an 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 ppm. This is the highest since the beginning of continuous monitoring in 1959, states the report. The growth rate of atmospheric carbon dioxide is significantly larger than those for the 1980s and 1990s, which were 1.58 and 1.49 ppm per year, respectively. The present atmospheric concentration of carbon dioxide is 381 ppm, the largest concentration in the last 650,000 years, and probably in the last 20 million years:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: climate change :: carbon dioxide :: greenhouse gas emissions :: fossil fuels :: carbon sinks ::

While the worldwide acceleration in carbon dioxide emissions had been previously noted, the current analysis provides insights into its causes. “The new twist here is the demonstration that weakening land and ocean sinks are contributing to the accelerating growth of atmospheric CO2,” says co-author Chris Field, director of the Carnegie Institution’s Department of Global Ecology.

Changes in wind patterns over the Southern Ocean resulting from human-induced global warming have brought carbon-rich water toward the surface, reducing the ocean’s ability to absorb excess carbon dioxide from the atmosphere. 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 paper presents "a consistent picture of the increasing accumulation of atmospheric CO2 and, hence, the increasing urgency to do something about it," says physical scientist S. Randy Kawa of NASA's Goddard Space Flight Center in Greenbelt, Maryland. But he cautions about jumping to long-term conclusions. "Just because the last 7 years have shown accelerating trends does not mean that the next 7 or 50 or 100 will be the same," Kawa says. "But they are what they are, and we need to pay attention."

The research team included scientists from the following institutions: CSIRO Marine and Atmospheric Research (Australia); the International Institute for Applied Systems Analysis, Laxenburg (Austria); the Commissariat a L'Energie Atomique, Laboratorie des Sciences du Climat et de l'Environnement (France); University of East Anglia, School of Environment Sciences, Norwich, (UK), the British Antarctic Survey, Cambridge (UK); the Carnegie Institution of Washington, Department of Global Ecology, Stanford (USA); the NOAA Earth System Research Laboratory, Boulder (USA); the Woods Hole Research Center, Falmouth (USA); and the Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge (USA).

References:
Michael R. Raupach, Gregg Marland, Philippe Ciais, Corinne Le Quéré, Josep G. Canadell, Gernot Klepper, and Christopher B. Field, "Global and regional drivers of accelerating CO2 emissions", PNAS, June 12, 2007, vol. 104, no. 24, 10288-10293

Eurekalert: Rise in atmospheric CO2 accelerates as economy grows, natural carbon sinks weaken - October 22, 2007.

GLobal Carbon Project: "Recent Carbon Trends and the Global Carbon Budget updated to 2006" [*.pdf], GCP-Global Carbon Budget team: Pep Canadell, Philippe Ciais, Thomas Conway, Chris Field, Corinne Le Quéré, Skee Houghton, Gregg Marland, Mike Raupach, Erik Buitenhuis, Nathan Gillett; Last update: 20 October 2007

The 6 emissions scenarios developed by the International Panel on Climate Change and still used as the reference can be found here: IPPC Special Report: Emissons Scenarios, Summary for Policy Makers [*.pdf] - 2000.