The Southern Ocean's ability to absorb carbon dioxide has decreased by 15% since 1981 and climate change is likely to blame, according to a new study published in Science.
The Southern Ocean surrounds the continent of Antarctica and extends up to 60 degrees south latitude. An international team of researchers documented the decline in the Southern Ocean's ability to absorb carbon dioxide after four years of study.
“The researchers found that the Southern Ocean is becoming less efficient at absorbing carbon dioxide due to an increase in wind strength over the Ocean, resulting from human-induced climate change,” said Dr Paul Fraser, who leads research into atmospheric greenhouse gases at Australia's CSIRO Marine and Atmospheric Research Division.
Ocean's are an important natural absorber and reservoir, or "sink," for carbon dioxide emissions. Such a weakening in the ocean's ability to absorb and sequester carbon dioxide would mean higher atmospheric concentrations of carbon dioxide, which in turn would accelerate global warming.
This potential feedback effect - where warming temperatures weaken natural carbon sinks, which in turn increase carbon dioxide levels in the atmosphere, driving further global warming - are taken into account by many new climate models. However, most models do not predict a weakening in oceanic carbon sinks for another forty years.
[Image: The natural carbon cycle. Oceans are one of two major natural carbon sinks, the other being terrestrial 'biospheres.']
While man-made greenhouse gas emissions from the burning of fossil fuels are only a small part of the total transfer of carbon dioxide in the carbon cycle, these man-made sources overwhelm a balanced natural system and lead to an increase in atmospheric levels of carbon dioxide, a greenhouse gas. This in turn causes global warming, which may weaken the ability of natural carbon sinks to absorb carbon, further accelerating climate change.
Carbon dioxide is naturally exchanged between the atmosphere and the upper layers of oceans. However, as ocean waters circulate, some carbon dioxide is driven to deeper layers of the ocean where it is stored in the world's largest natural reservoir of carbon dioxide.
The new study's researchers found that increased wind speeds over the Southern Ocean have influenced the process of mixing and upwelling in the ocean, which has resulted in an increased release of carbon dioxide from the oceans into the atmosphere. This decreases the net absorption of carbon carbon dioxide into the ocean and leaves more of the greenhouse gas in the atmosphere.
Humans Likely To Blame
The researchers also found that the increase in wind strength is due to a combination of higher levels of greenhouse gases in the atmosphere and long-term ozone depletion in the stratosphere, both driven by human activities.
The report's lead author, Dr Corinne Le Quéré, of UEA and BAS said:
“This is the first time that we’ve been able to say that climate change itself is responsible for the saturation of the Southern Ocean sink. This is serious. All climate models predict that this kind of ‘feedback’ will continue and intensify during this century. The Earth’s carbon sinks – of which the Southern Ocean accounts for 15 per cent – absorb about half of all human carbon emissions. With the Southern Ocean reaching its saturation point more CO2 will stay in our atmosphere.”This new research suggests that stabilization of atmospheric concentrations of greenhouse gases at a level that will prevent dangerous climate change is even more difficult to achieve than previously thought.
Additionally, the report's authors warn that acidification in the Southern Ocean is likely to reach dangerous levels earlier than the projected date of 2050. As oceans absorb carbon dioxide, it alters the pH of the ocean waters, making them more acidic. This will have adverse impacts on ocean species, including corals and some kinds of plankton.
Professor Chris Rapley, Director of British Antarctic Survey said:
“Since the beginning of the industrial revolution the world’s oceans have absorbed about a quarter of the 500 gigatons of carbon emitted into the atmosphere by humans. The possibility that in a warmer world the Southern Ocean – the strongest ocean sink - is weakening is a cause for concern.”The international research team collected atmospheric CO2 data from 11 stations in the Southern Ocean and 40 stations across the globe. Measurements of atmospheric CO2 allowed them to infer how much carbon dioxide was taken up by sinks. The team was then able to see how efficient they were in comparison to one another at absorbing CO2.
The international team comprised researchers from CSIRO in Australia, the Max-Planck Institute in Germany, the University of East Anglia and British Antarctic Survey in England, the Climate Monitoring and Diagnostics Laboratory in the US, NIWA in New Zealand, the South African Weather Service, LSCE/IPSL and CNRS in France, and the Centre for Atmospheric and Oceanic Studies in Japan.
This is really scary news!
The world’s oceans are one of two main carbon ’sinks’ - absorbers of carbon dioxide from the atmosphere, that in the natural carbon cycle help keep greenhouse gas levels in the atmosphere in check. As we destabilize the natural carbon cycle with man-made greenhouse gas emissions, we cause global warming which in turn is expected to weaken the ability of the oceans to absorb carbon dioxide, leading to a further buildup of atmospheric carbon dioxide levels, driving further warming. This is just one of many powerful feedback mechanisms that could push climate change beyond our ability to halt.
Climate models and the IPCC reports take this feedback into account, but generally do not assume it will kick in until mid-century. If the ability of the world’s oceans to absorb carbon dioxide is already beginning to decrease, we will need to recalculate the speed and severity at which the world must cut greenhouse gas emissions in order to stabilize the climate and avoid disastrous climate change.
It’s definitely time to get serious about cutting greenhouse gas emissions as hard and as fast as possible. And the United States needs to lead the way. We need to begin a bold plan to cut emissions as quickly as possible by the end of the next decade, perhaps by 30-60 percent, levels even greater than the supposedly ‘gold standard’ Sanders-Boxer Global Warming Pollution Reduction Act proposes (it calls for about a 15% cut by 2020).
When we read news like this, it’s clear that time is definitely running out!
[Image source: BBC News. A hat tip to Green Car Congress.]