Two New Views Of Carbon Sinks
August 2, 2012

Greenhouse Gas Continues To Be Absorbed By Carbon Sinks

April Flowers for - Your Universe Online

In the last 50 years, man has quadrupled his CO2 output, primarily through the burning of fossil fuels. That is a startling and sobering concept. So far, though, Mother Nature seems to be keeping pace.

In a new study released August 2, 2012, in the journal Nature, researchers from NOAA and the University of Colorado assert that Earth's carbon sinks continue to soak up roughly half of the carbon output. Carbon sinks are areas of carbon storage, whether by land or sea. The scientists analyzed 50 years of global carbon dioxide (CO2) measurements and found that the processes by which the planet's oceans and ecosystems absorb greenhouse gas are not yet at capacity.

"Globally, these carbon dioxide 'sinks' have roughly kept pace with emissions from human activities, continuing to draw about half of the emitted CO2 back out of the atmosphere. However, we do not expect this to continue indefinitely," said NOAA's Pieter Tans, a climate researcher with NOAA's Earth System Research Laboratory in Boulder, Colorado.

"What we are seeing is that the Earth continues to do the heavy lifting by taking up huge amounts of carbon dioxide, even while humans have done very little to reduce carbon emissions," said Ashley Ballantyne, University of Colorado post-doctoral researcher and lead author agrees. "How long this will continue, we don't know."

Tans, Ballantyne and colleagues at the University of Colorado, including the Cooperative Institute for Research in Environmental Sciences (CIRES), dissected the long-term records of CO2 levels measured by NOAA and the Scripps Institution of Oceanography at more than 40 remote sites around the world, including the top of a mountain in Hawaii and the South Pole. Those CO2 levels reflect global averages of the greenhouse gas, which are affected by natural cycles as well as people's activities.  The researchers also looked at national and international inventories and estimates of CO2 emissions by people and compared those to atmospheric levels of the gas.

Carbon dioxide is emitted into the atmosphere mainly by fossil fuel combustion, but also by forest fires and other natural processes. The gas is pulled out of the atmosphere into the tissue of growing plants or absorbed by the Earth's oceans. The rest accumulates in the atmosphere, where it is likely to accelerate global warming.

A series of recent studies suggested that the natural carbon sinks might not be keeping up with the increasing rate of emissions, which could cause a rise in atmospheric CO2 and climate change impacts.

Ballantyne and Tan, however, saw no faster-than-expected rise. They, and the rest of the team, warn that this can't continue indefinitely. It's not a question of whether or not the Earth will lose the race to soak up the CO2, its merely a question of when.

"We're already seeing climate change happen despite the fact that only half of fossil fuel emissions stay in the atmosphere while the other half is drawn down by the land biosphere and oceans," Caroline Alden, University of Colorado-Boulder said. "If natural sinks saturate as models predict, the impact of human emissions on atmospheric CO2 will double."

Recent studies have shown that carbon sinks were declining already in some parts of the world, including the Southern Hemisphere and portions of the oceans. The carbon that is being pulled from the atmosphere isn't really disappearing either. It is still present in the soil and vegetation.  Dissolved CO2 in the oceans is making them more acidic, as well, damaging coral reefs which house 25 percent of the world's fish populations. Oceans can store carbon for centuries. Plants and trees return the CO2 through respiration or forest fires much sooner. Tan warns that man's carbon output is pushing the system out of equilibrium.

Despite the heroic efforts of the Earth's ecosystem to keep up, CO2 in the atmosphere has climbed from 280 parts per million just prior to the Industrial Revolution to 394 parts per million today, and that rate of increase is speeding up. The atmospheric saturation is expected to reach 400 parts per million by 2016.

A total of 33.6 billion tons of CO2 were emitted globally in 2010, climbing to 34.8 billion tons in 2011, according to the International Energy Agency. Federal budget cuts to U.S. carbon cycle research are making it more difficult to measure and understand both natural and human influences on the carbon cycle, according to the research team.

"The good news is that today, nature is helping us out," said CU-Boulder Professor Jim White. "The bad news is that none of us think nature is going to keep helping us out indefinitely. When the time comes that these carbon sinks are no longer taking up carbon, there is going to be a big price to pay."

In a related study, published in Proceedings of the National Academy of Sciences, a team of researchers has been studying the economics of carbon credit schemes, tradable certificates or permits representing the right to emit one ton of carbon or another greenhouse gas, to protect and increase necessary carbon sinks. Specifically, the team has been studying mangrove habitats.

Mangroves are important for biodiversity, fishing habitats and storm protection barriers. They are home to hundreds of species of plants and animals, many of them endangered. Mangroves capture carbon, on average, about five times more than tropical rainforests, so they are invaluable as carbon sinks as well.

The problem is that mangrove habitats only comprise less than 1% of all forest areas across the globe, and they are being lost at a faster rate than those tropical rain forests. So far, conservation efforts have centered mainly on the carbon emissions aspect to push for the reforestation of mangrove swamps.

Now, Dr. Juha Siikamaki, of the think tank Resources for the Future and his US colleagues have shown that protecting mangroves and thereby reducing the amount of CO2 released may be an affordable way for countries to mitigate their carbon emissions.

"We make the surprising finding that in most places, preserving mangroves is justified solely based on the avoided emissions, without any regard for the many other ecological and economic benefits mangroves are particularly well known for," Dr Siikamaki told BBC News.

The team used high resolution surveys of global mangrove biomass to conclude that protecting mangrove habitats could be a viable means for reducing emissions in comparison to other carbon offset methods.

Not everyone is convinced, however. The Carbon Brief, a fact checking service, asserts that the price of carbon, on which the research is based, has decreased making the findings outdated. Carbon prices have dropped due to an over-supply of permits and poor economic conditions, decreasing competition and dropping the prices. Although other incentive programs are available, the research team is adamant that the preservation of mangroves is cheaper.

The mangrove recommendations resemble another program called REDD (Reducing Emissions from Deforestation and forest Degradation).  REDD gives nations financial incentives for reducing deforestation, leading to decreases in carbon emissions.

"Projects that involve and respect local people and that use the market for carbon offsets to fund development and conservation are beginning to emerge," Professor Mark Huxham of Edinburgh Napier University.