World leaders are meeting at the United Nations on Tuesday to discuss climate change and possible solutions.

Much of the focus is on how to cut back on CO2, the primary greenhouse gas scientists say is driving global warming. But, in the past week, some of the largest U.S. companies have agreed to phase out use of another greenhouse gas, hydrofluorocarbons, or HFCs.

Though a much smaller share, HFCs have a much higher planet-warming potency than CO2.

Dr. Michael Prather is a professor of earth system science at the University of California, Irvine and one of the lead authors on the recent climate change assessment from the United Nations. He says carbon dioxide comes from burning carbon fossil fuels and deforestation. 

"HFCs, hydrofluorocarbons, are really technology gases," Prather says. "They don't occur naturally; we make them. They're all synthetic. And they get released by their technology use."

They're held in air conditioners, refrigerators, heat pumps, truck, trailers, fire fighting equipment and other places, he said. They're eventually released, float around in the atmosphere until they get destroyed chemically.

Lifetimes for HFCs are 1 to 50 years, he said, while CO2 lifespan is much longer.