Choose the best answer.

Passage 3

1     Chemicals from air-conditioning units and refrigerators in daily use throughout Asia could cause     catastrophic climate change unless we change our ways soon, scientists say. Called hydro chlorofluorocarbons (HCFCs), the chemicals were widely adopted about 20 years ago after it was discovered that the chemicals being used until then – chlorofluorocarbons (CFCs) – had been depleting the ozone layer.

2     The scientists say what has been beneficial for the ozone layer could be disastrous for the world‘s climate, because HCFCs turn into “super greenhouse gases”, some of them nearly 5,000 times stronger than carbon dioxide.

3     As long as they stay inside our air-conditioners and refrigerators, HCFCs are harmless coolants, colorless and odorless. But when they leak into the air, they become what scientists call fluorinated greenhouse gases, or F-gases.

4     Unfortunately, leaks are normal. Most residential air-conditioners have natural leakage of 5% per year, according to the UN. Poor maintenance can increase that to 50%. And if the machine is dumped without recovering the coolant, the figure jumps to 100%.

5     A report published earlier this year shows that in a worst-case scenario F-gases could be responsible for as much as 45% of total global warming by 2050, and Asia will be the main contributor.

6     “F-gas emissions in developing countries are projected to be as much as 800% greater than in     developed countries in 2050,” reports a climate scientist working under Guus Velders of the Netherlands Environmental Assessment Agency.

7     Alarm bells have not stopped ringing since his report came out in June, and the race is now on     to deploy substitutes for F-gases which otherwise will wipe out much of the potential benefit of     whatever agreements emerge from climate talks in Copenhagen next month.

8     The UN agencies involved with climate change knew all along that F-gases had high global-warming potential, but they said the amounts involved were so small that they wouldn‘t have a significant impact.

9     The chemical companies also knew of the dangers, but they continued to lead their shareholders to believe that F-gases were good for the environment.

What releases the highest level of greenhouse gases in the environment?