CO2 Levels Rising Faster Than Forecast

The journal Proceedings of the National Academy of Sciences has published an article that finds that atmospheric concentrations of greenhouse gases are rising faster than projected. We reported recently on the fact that oceans are becoming less effective as a carbon sink, an idea independently confirmed by Dr. Corinne Le Quere, of the University of East Anglia and the British Antarctic Survey and Chris Field of the Carnegie Institution.

From PhysOrg.com:

Human activities are releasing carbon dioxide faster than ever, while the natural processes that normally slow its build up in the atmosphere appear to be weakening. These conclusions are drawn in a new study in the early online edition of the Proceedings of the National Academy of Sciences, October 22-26. The report states that “together, these effects characterize a carbon cycle that is generating stronger-than-expected climate forcing sooner than expected.”
Between 2000 to 2006, human activities such as burning fossil fuels, manufacturing cement, and tropical deforestation 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 parts per million (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.

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.

Further reporting from the Guardian:

Levels of carbon dioxide in the atmosphere have grown 35% more quickly than expected since 2000 because of inefficiency in fossil fuel use and the weakening of natural “carbon sinks”, scientists warned.

Increasing use of coal-fired power stations and a lack of technological improvements has led to a 17% increase of CO2 above expected levels, researchers at the University of East Anglia (UEA) said.

There has also been a decrease in the ability of land and oceans to absorb carbon dioxide, with the decline in efficiency of these natural sinks accounting for increases 18% above anticipated levels since 2000.

Over half the decline of the carbon sink efficiency is the result of intensifying winds in Antarctica’s Southern Ocean disrupting the sea’s ability to store carbon, the scientists from UEA, the British Antarctic Survey and the Global Carbon Project said.

The latest warning on rising CO2 levels, and its implications for climate change, is being published in the journal Proceedings of the National Academy of Sciences (PNAS). It comes just days after other researchers at UEA revealed that measurements of the north Atlantic from the mid-1990s to 2005 showed the level of carbon dioxide in its waters reduced by about half over the decade.

The new study’s author Dr Corinne Le Quere, of UEA and the British Antarctic Survey, said winds were intensifying in the Southern Ocean because of climate change and depletion of the ozone layer.

The stronger winds were causing more “mixing” of the waters, bringing carbon up from the deep seas where it was stored and raising the carbon concentration of the surface water, which allowed less CO2 to dissolve into the ocean from the atmosphere. A decrease in fossil fuel efficiency is also speeding up the increase in atmospheric carbon dioxide levels, she said.

“What happened for 30 years is that we became more efficient in producing wealth from our emissions, but that has stalled since 2000. There’s a slow change from oil and gas to coal which is more CO2 intensive. As developing countries grow so does their use of energy and coal is easier to access and cheaper.

“Developed countries have not been providing massive investment in technology to counteract that. We had anticipated that the growth in CO2 would follow the world economy but we had not anticipated that we would not be as efficient as we were being and the sinks would not respond,” Dr Le Quere said.

And she warned: “The decline in global sink efficiency suggests that stabilisation of atmospheric CO2 is even more difficult to achieve than previously thought.”

Further reporting from PhysOrg.com: