Synthetic gases developed as a "safer" replacement for chlorofluorocarbons which caused the hole in our planet's ozone layer above Antarctica can still represent a risk, MIT scientists say.
When chlorofluorocarbons, or CFCs, were phased out by international agreements because of their recognized risk, a new class of supposedly safer synthetic gases replaced them. However, their possible contribution to climate change has been little-studied by the scientific community.
An international team of researchers, including the MIT scientists, studied the level of these synthetic types of greenhouse gases (SGHGs) from 1978 to 2012 to predict the impact they may have on global warming through 2050.
"Left unchecked, synthetic greenhouse gases have the potential to cause significant further warming," says MIT's Ronald Prinn, co-author of the study predicting the warming potential of 25 of the most common SGHGs.
Unless limits are put in place on the use of SGHGs, we could see an increase in global warming that may negate the climate improvements from phasing out CFCs agreed to in the 1987 Montreal Protocol.
With the withdrawal of CFCs, the utilization of alternate synthetic gases including hydrofluorocarbons (HFCs), mostly in refrigeration systems, has increased, and while they had come under limitations in the presently moribund 1997 Kyoto Protocol, there are currently no restrictions on their use.
Taking HFCs as a subject model, the researchers analyzed what the effect would be if the Montreal Protocol were amended and include this class of synthetic gases.
"We could avoid adding the equivalent of up to another three years of carbon dioxide emissions into the atmosphere if these gases were being phased down," says lead author Matthew Rigby of the University of Bristol in England.
HFCs are exceptionally strong types of greenhouse gases, he says, so at even relatively low levels they can add to atmospheric warming.
"Per ton of emissions, HFCs are much more potent greenhouse gases than carbon dioxide, and are very good at trapping the radiation that heats the Earth," Rigby says.
Although carbon dioxide remains the major factor in climate change, HFCs, if not reduced could be a significant factor in future warming.
"Addressing HFCs, and other SGHGs, now will ensure that they don't contribute significantly to warming in the future," Prinn says.
Even with the restrictions on CFCs, the researchers warn they will be an ongoing contributor to global warming for the foreseeable future because of their persistence in the atmosphere.
"CFCs have contributed the most among the synthetic greenhouse gases to warming," Prinn says. "Their use peaked and levels are now declining, but these gases will remain in the atmosphere for many years. This is likely the trend we will see with most SGHG gases, so it is important that we address these gases now before they do more severe damage."
The researchers based their findings on measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE), a world-wide observing system developed by MIT researchers and other scientists sponsored by NASA and several other agencies.
