the hole in the ozone layer -- are making the current one worse. The chemicals, called hydrofluorocarbons (HFCs), were introduced widely in the 1990s to replace ozone-depleting gases used in air conditioners, refrigerators and insulating foam. They worked: The earth's protective shield seems to be recovering. But researchers say what's good for ozone is bad for climate change. In the atmosphere, these replacement chemicals act like 'super' greenhouse gases, with a heat-trapping power that can be 4,470 times that of carbon dioxide. Now, scientists say, the world must find replacements for the replacements -- or these super-emissions could cancel out other efforts to stop global warming. 'Whatever targets you thought you were going to make,' said David Fahey, a physicist at the National Oceanic and Atmospheric Administration, 'it will be undermined by the fact that you have ... additional emissions that you hadn't planned on.' The colorless, odorless replacement chemicals enter the atmosphere in tiny amounts, often leaking out of refrigerators and air conditioners, or escaping when those machines break and are improperly dumped. They now account for about 2 percent of the climate-warming power of U.S. emissions, according to the Environmental Protection Agency. That is still far less than carbon dioxide, which is produced by burning fossil fuels and accounts for about 85 percent of the problem. And it is less than the roughly 10 percent of warming from methane, which comes from sources including farm animals and decomposing trash. But in recent weeks, these obscure gases have been given a higher profile in the carbon-dominated debate on climate change. Last month, a group of scientists published a paper projecting that, if unchecked, the emissions would rise rapidly over the next 40 years. By 2050, they found, the amount of super greenhouse gases in the atmosphere might be equal to six or more years' worth of carbon dioxide emissions. And last week, diplomats met in Geneva to discuss ideas for a worldwide reduction in HFCs. 'You have this moment when you could nip this problem in the bud and avoid this very large growth of a dangerous chemical,' said David Doniger, policy director at the Natural Resources Defense Council's climate center, from Geneva. 'Now, in the next couple of years, is when you have to do this.' The roots of the problem go back to the 1970s, when scientists theorized that chemicals called chlorofluorocarbons (CFCs) were slowly eroding stratospheric ozone. That was a dangerous thing, since the ozone layer protects the planet from harmful UV radiation. In 1987, governments signed the Montreal Protocol, agreeing to reduce CFCs. Since then, this agreement has been a kind of bureaucratic miracle: Ninety-six percent of ozone-depleting substances have been phased out, according to the United Nations. The United Nations says there is still a hole in the ozone above the South Pole, but global ozone levels are expected to return to their pre-1980 level by about 2050. 'If this were a soccer team ... it's won every single game,' said Durwood Zaelke, president of the Institute for Governance and Sustainable Development. 'That's astounding in the international environmental field.' It worked because chemists engineered substitutes for CFCs, new gases without the propensity to chemically unlock ozone molecules. The replacements could still chill cold cuts and Chevrolets -- in refrigerators and under car hoods, they are compressed and uncompressed in a process that sucks heat out of passing air. But the chemicals' strong bonds also cause them to act as heat sponges in Earth's atmosphere, absorbing energy from the sun and keeping it from being reflected out into space. In the 'blanket' created by heat-trapping gases, that makes them especially heavy strands. 'Pound for pound, they're much more powerful than CO2, you know -- hundreds or thousands of times more powerful,' said NOAA physicist Fahey. Exactly how powerful depends on the makeup of the gases. One, common in fridges and auto air conditioners, lasts 12 to 14 years in the atmosphere and has 1,430 times the global warming impact of carbon dioxide. Another has a 52-year life and 4,470 times the power. According to the recent paper, there will soon be many more of them, as developing countries become more prosperous and their people buy vehicles and air conditioners. Even if the world makes significant progress in reducing carbon dioxide and methane -- still a big if, since recent negotiations on the topic have produced little -- the scientists said the growth in HFCs could undo a significant part of their work. Internationally, the gases are still supposed to be dealt with in the same vast and balky negotiations that will reduce carbon dioxide. So they will probably be on the table when diplomats gather in Copenhagen in December to create a successor to the Kyoto Protocol of 1997. But many environmental groups, including the nonprofit Environmental Investigation Agency, say they would like to see the gases regulated using the Montreal Protocol, because the framework succeeded in dealing with other pollutants. 'The climate problem is not one global problem. It's a package of global problems,' said Zaelke, of the Institute for Governance and Sustainable Development. 'You can reach in and pull out a piece.' Sens. John F. Kerry, D-Mass., and Barbara Boxer, D-Calif., who chair two powerful committees, urged this approach in a letter to President Obama in April. Last week, an official said the administration was still deciding what approach to support. A bigger question: What will replace these chemicals? Experts say that some substitutes, with less global warming impact, can be made with new HFCs or by using ammonia or butane. But others are needed. 'We don't know all of them yet,' said Mack McFarland, global environmental manager for DuPont Fluoroproducts, a division of Delaware-based DuPont. 