Science finds greenhouse gases even stronger than CO2, methane

While greenhouse gases like carbon dioxide and methane get all the attention, the man-made chemicals we use in air conditioning and manufacturing have even greater warming potential, new research has found.

In fact, compounds with fluorine show the most potential for slamming shut the so-called “atmospheric window,” an infrared frequency through which heat from Earth is released back into space. Rather than gradually closing that avenue of cooling, like carbon dioxide does, fluorinated compounds could cut it off quickly, according to a new study by scientists at Purdue University and NASA.

While the Intergovernmental Panel on Climate Change (IPCC) has identified a host of chemicals beyond the usual culprits (carbon dioxide, methane nitrous oxide, water vapour, etc.) as greenhouse gases, the Purdue and NASA researchers set out to identify exactly which of their chemical and physical properties are most important in contributing to global warming.

“Believe it or not, nobody has ever delineated these properties,” said Timothy Lee, a NASA scientist and co-author of the new study.

The research team found that compounds most efficient at trapping heat in the Earth’s atmospheric window are fluorine-containing chemicals like chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur and nitrogen fluorides.

“It’s actually rather stark,” said Joseph Francisco, a Purdue chemistry and earth and atmospheric sciences professor and another co-author of the study.

The fluorine atoms in such chemicals are highly electro-negative and tend to pull electrons to themselves. That makes the molecules more efficient at absorbing radiation which would otherwise normally bleed harmlessly into space. As a result, fluorine-containing compounds are the most effective global warming agents, the study found.

Fluorinated compounds also persist longer in the atmosphere than carbon dioxide and other major global warming agents, with some remaining stable for thousands of years. That raises the concern that, even if they’re emitted into the atmosphere in lower quantities, these chemicals might have a powerful cumulative effect over time.

By better understanding how chemicals contribute to climate change on a molecular scale, we can work to create benign alternatives and test new chemicals for their global warming capacity before they go to market, Francisco said.

“Now you have a rational design basis,” he said.

While CFC use has waned since we’ve learned how it damages the Earth’s ozone layer, HFCs and PFCs are widely used in air conditioning and the manufacturing of electronics, appliances and carpets. They’re also used as everything from a blood substitute in transfusions to a means of tracking leaks in natural gas lines.

“Although current concentrations of some of these trace gases have been found to be substantially small compared to carbon dioxide, their concentration is on the rise,” the study’s authors write. “With the current rate of increase, they will be important contributors in the future, according to some models.”

Also co-authoring the study, published in a special edition of the American Chemical Society’s Journal of Physical Chemistry, was NASA postdoctoral fellow Partha Bera.