More than 20 years ago, an international treaty known as the Montreal Protocol phased out a group of chemicals that were destroying the Earth's ozone layer.
But since then, scientists have discovered that some of the chemicals developed to replace those destructive compounds might be contributing to another problem: global warming.
These new chemicals are known as hydrofluorocarbons, or HFCs, and they're used as coolants in refrigerators. HFCs have largely replaced older refrigerants, such as CFCs. These replacements are nonflammable and don't hurt the ozone.
But when it comes to global warming, HFCs aren't so good, says Kert Davies of Greenpeace.
"We call them the super greenhouse gases," Davies says. "They're the global warming threat that no one has really heard about."
Super Greenhouse Gases
Greenhouse gases trap heat in the atmosphere. Molecule for molecule, HFCs are hundreds to thousands of times better at this than the most important greenhouse gas, carbon dioxide.
The good news is that, at the moment, HFCs are responsible for just a small percentage of human-induced global warming. The bad news is that global production of these chemicals is poised to take off, to satisfy the world's growing desire for refrigerators and air conditioners.
"Right now, what's happening is that China and India are beginning to invest very, very heavily in HFC production," said Samuel LaBudde of the Environmental Investigation Agency, a small nonprofit organization.
LaBudde's group started out investigating the illegal trade of ozone-destroying chemicals that had been banned. But they quickly realized that perfectly legal trade in the replacement HFCs could do far more damage.
By 2050, LaBudde says, the global warming from HFCs could cancel out all the reductions in carbon dioxide likely to emerge from the United Nations climate talks that will take place in Copenhagen in December.
Replacing The Replacement
Environmental groups have been trying to do something about HFCs for well over a decade.
So far, two small countries have proposed phasing out the chemicals by amending the 1987 Montreal Protocol. And last week, the United States, Canada and Mexico agreed to support a treaty amendment that would dramatically reduce HFC production.
Of course, that would mean the air-conditioning and refrigeration industries will have to find yet another chemical.
Some companies are already testing soda vending machines that use carbon dioxide as a coolant instead of HFCs. Carbon dioxide is a greenhouse gas, but the machines use so little that it would have almost no effect on global warming.
Carbon dioxide doesn't work in all refrigerators. But other alternatives, like propane and isobutane, do. In fact, those chemicals are already in 100 million refrigerators worldwide.
So does that mean our HFC problem is solved?
Probably not, says Karim Amrane, vice president of regulatory policy and research at the Air Conditioning, Heating and Refrigeration Institute trade group.
Amrane says chemicals like isobutane are a problem because they burn.
"Imagine if you had 1,000 pounds or more of isobutane in your chiller in this building, and something happened," he says. "The entire building probably will be wiped out."
Even so, his industry knows HFCs eventually have to go.
Now they are left with the difficult task of finding substitutes that will solve the current problem, without creating yet another.