New Research Suggests Feedback Amplification of Emissions on Natural Carbon Cycle Lower Than Expected
More CO2, more heat. More heat, more CO2. In its essence, that is the relationship of the positive feedback loop thought to fuel an rising global temperatures and CO2 emissions in the atmosphere.
All systems run in a state of balance. A change in one part of the system alters that balance and effect changes throughout the system as it finds a new balance - or spins wildly out of control. The more complex the system, the harder it is to tell exactly at what point gentle readjustments become wrenching disruption. Such is climate science.
One aspect of that science has been the study of the suspected "positive feedback" loop between rising CO2 levels from carbon emissions resulting in rising temperatures that reduce the capacity for natural systems - ocean and forests for instance - to absorb CO2. This in turn leads to increased levels of CO2, more warming, and an amplification of the natural carbon cycle in a "vicious" cycle of accelerating change.
Just how much of this positive feedback loop occurs - what scientists call the "feedback coefficient" - remains an unresolved question, and this uncertainty has led to a wide range of current warming projections. Recent research has suggested that a one degree Celsius rise in temperature could lead to an increase of up to 40 parts-per-million (ppm) of CO2 concentration in the atmosphere, thus adding a considerable amplification to the ongoing steady rise in CO2 concentrations. But scientists have also had to deal with a range of error up to 30 ppm. It becomes apparent why projecting future CO2 levels and temperatures is so difficult.
A new study published last week in the journal Nature suggests that, while there is an amplifying positive feedback loop between emissions and rising temperatures, it may be significantly less than previously suspected. Researchers in Germany and Switzerland say that instead of up to a forty ppm increase with each one degree C rise in temperature, the feedback coefficient is on the order of a 1.7 to 21.4 ppm rise in CO2, with an average 7.7 ppm.
The study's lead author, David Frank from the Swiss Federal Research Institute, says he is confident of his conclusions because he his fellow researchers based their study on considerably more data than in previous research.
Frank's study used three Antarctic ice core samples and compared the CO2 record stored in the air bubbles trapped inside those cores with 9 global-scale temperature reconstructions to calculate how atmospheric CO2 levels changed during the period from 1050 to 1800. Frank and his team compared 200,000 ice core readings with temperature records derived from tree rings, sediments and other natural "proxy" temperature records.
The painstaking analysis led to the conclusion that there is a 95 percent possibility that the 40 ppm estimation is too high.
Our analysis considered significantly more data than previous approaches," Frank said. "By looking at all possible relationships between available temperature CO2 data, we are able to show that past feedbacks of 40 ppm [per degree Celsius] or greater were unlikely."
That's good news, but doesn't erase the fact that emissions have an amplifying effect on a warming climate, and remains a cause for concern.
By showing that the feedback in the past was positive," Frank said, "[that] gives us a strong indication that the ocean and terrestrial ecosystems will amplify anthropogenic warming."
In other words, while not as bad as once feared, the study shows that the relationship between emissions and temperature has a "positive coefficient" and that Earth's bio systems won't be able absorb all of mankind's carbon emissions.
More CO2, more heat. More heat, more CO2.
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