Use of HCFC-22 has soared in the third world with the economic growth of China, India and other countries, along with the sharp drop in air-conditioner costs that has accompanied China’s growing skill in making them cheaply. Mr. Seebaluck said Mauritius’s use of HCFC-22 had risen more than 100-fold in the last six years because of a boom in hotel construction and the rapid expansion of the fishing industry, which uses a lot of refrigeration to preserve freshness.

The use in India and China, far larger markets, has been rising as much as 35 percent a year lately, with specialists predicting that similar growth could last through 2016.

Industrial nations are required to phase out HCFC-22 by 2020, but most are moving faster. The European Union phased it out in 2004. The United States will ban domestic production in 2010 and is considering whether to ban imports then, as well.

China has begun making air-conditioners with more modern refrigerants for the European market. But by continuing to produce HCFC-22 for markets elsewhere, the Chinese have been able to claim hundreds of millions of dollars a year in payments from an obscure United Nations agency.

The payments are to compensate Chinese chemical factories for incinerating a waste gas generated as part of the manufacturing process for HCFC-22. If the Chinese industry switches to modern refrigerants, it would no longer produce the waste gas and so would lose the credits.

India has a large and growing HCFC-22 industry that is also reaping a fortune in credits. But the Indian government has largely stayed on the sidelines in international talks, while China has called for industrial nations to pay even more for the incineration of waste gases from HCFC-22 production; China proposes to spend much of that to develop its renewable-energy industry.

A big problem is that no one has agreed what should replace HCFC-22. The chemicals requiring the fewest changes to air-conditioner designs avoid harm to the ozone layer but are still as potent, gram for gram, in terms of global warming.