There's good news and bad news about hydrofluorocarbons (HFCs), the gases that replaced the ozone-depleting substances that were used in refrigerators and air conditioners.

The good news: HFCs are indeed much less damaging to Earth's protective ozone layer. But, the downside is that many of the HFCs currently in use are strong greenhouse gases, and they have been increasing rapidly in the atmosphere.

More: HFC Greenhouse Gases: A Tale of Two (or more) Futures