Alarms sounded in 1985 when three British researchers found the ozone layer over the Antarctic was abnormally thin. Scientists had reason to be worried. As ozone exists in the stratosphere, 20 to 50 kilometers about the surface of the earth, it is our only protection against the dangerous ultraviolet radiation given off by the sun.

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For human beings, too much of that radiation increases risk of skin cancer, cataracts, immune system weakness and other disorders related to DNA alteration. In fact, without ozone all life on the planet would be threatened. Ultraviolet-B rays also harm animals, hinder production of phytoplankton � a basic part of the food chain in the sea � and slow the growth of plants, with dangerous consequences for farming.

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For this reason, once it learned of the hole in the ozone layer, the world jumped into action. That same year the Vienna Convention proposed voluntary measures to reduce emissions of ozone-destroying substances. These had been identified by the scientists Rowland and Molina. In 1974 they linked decreases in the ozone layer with emission into the atmosphere of chlorofluorocarbons (CFCs). These are gases used since the 1930s in many applications: coolants for refrigerator and air conditioning circuits, aerosol� propellants, solvents and other uses.

In 1987 the ozone layer had dwindled to half its 1970 thickness. It was then that government recognized the need for drastic measures. On Sept. 16, 1987 the Montreal Protocol was signed in Canada, establishing a timetable for reducing and eventually eliminating production and consumption of CFCs and halons. The latter are gases used in fire extinguishers; they, too, destroy ozone.

The ozone layer has thinned approximately 6% a year since the 1970s. The land surface affected by the hole grew until it hit 20 million square kilometers in the 1990s. Since then it has varied between 20 million and 29 million. In 2001 the figure was 25 million. Just two months ago, Mario Molina, who won the Nobel prize for chemistry in 1995 for his work on how CFCs affect ozone, said the hole appeared to have stabilized but that it will take another 20 years for it to start to shrink. He and other experts say the layer will not have regenerated until 2050, assuming international agreements designed to save the layer are fulfilled.

The outlook was gloomy even though, thanks to the Montreal Protocol, production of CFC and halons dropped by 87% from 1987 to 1999. The problem is that there are other substances that destroy ozone, such as HCFCs, which are temporary substitutes for CFCs, or methyl bromide, used as a pesticide since the 1930s. These substances are subject to timetables for reducing and eliminating their use, but for a few more years they will continue to be employed. Furthermore, Molina says CFCs can remain in the environment for decades, and some of them for almost a century. The effects we see today on the ozone layer are due to compounds released one, five, 10 or 15 years ago. Also, CFCs are still used in developing countries, for which the Montreal Protocol extended until 2010 the deadline for eliminating the chemicals.

You yourself can help regenerate the ozone layer. Manufacture and sales of CFCs has been banned in Spain since 1995, but your refrigerator or air conditioning may have been built before then. The air conditioning in your car might also still use CFCs. If that is the case, make sure they are not leaking. And if you need to refill those circuits make sure to insist on recycled CFCs.

If you are going to buy a refrigerator make sure it is Greenfreeze technology that uses natural hydrocarbons � propane, isobutane or cyclopentane � as coolants. To check, look at the compressor on the back side. If it says R-600a, that�s Greenfreeze. If it says R-12 for R-134a, it is not. In Spain most home air conditioning units still use as a coolant the HCFC R-22, although things are starting to change. For now the least harmful solution is to use an appliance that takes hydrofluorocarbon (HFC) coolants like R-407 or R-410, which are free of chlorine. They don�t destroy the ozone layer but they do contribute to global warming. And make sure you get rid of your old fridge at a so-called Clean Point � ask in your town hall � so that the CFCs can be removed properly by an authorized waste handler.

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Did you know that?
- The record for the land surface affected by the hole in the ozone layer was set on Sept 12, 2000: 29 million square kilometers, or more than 57 times the area of Spain. The lowest value at the South Pole, 86 Dobson units, was recorded on Oct. 12, 1993. The level should be 460 units.

- These days methyl bromide is responsible for 5 to 10% of ozone layer loss. The bromine it contains is 50 times more harmful for the ozone layer than the chlorine in CFCs.

- Spain consumes 4,238 tons of methyl bromine a year, 5.6% of the world total. A report by the Montreal Protocol says that there are alternatives for 90 % of the uses of this substance, the Spanish government argues that it is irreplaceable for growing strawberries, peppers and tomatoes.

- The Montreal Protocol has been revised four times. The last list of ozone-destroying substances contained 96 compounds. Since 1987 it has been ratified by 186 countries.