The ozone layer that protects the earth from excessive solar radiation has suffered twice as much damage as expected, a United Nations environmental expert says.

The protective layer in the outer reaches of the earth's atmosphere is 4 percent thinner than it was in 1986, according to Dr. Mostafa Tolba, the executive director of the United Nations Environment Program.Last year, scientists predicted this year's reduction would only be 2 percent, Tolba told reporters Tuesday. He is in the Hague for a two-week conference on the ozone layer problem.

The sun's ultraviolet rays reaching the earth's surface unfiltered by the ozone layer have been linked to a variety of environmental and health problems ranging from stunted plant growth to skin cancer in humans.

It is also held partly responsible for the gradual heating of the earth's atmosphere known as the "greenhouse effect."

Damage to the ozone layer is mainly caused by a group of man-made chemicals known as chlorofluorocarbons or CFCs, which are widely used in aerosol cans, refrigerators, air conditioners and various types of plastic foam used for packaging and insulation.

The UNEP-organized gathering of scientists from more than 30 nations is the first meeting of its kind since last year's signing of the Montreal Protocol, which calls for the production of CFCs to be cut to half its 1986 levels by 1998.

However, Tolba said chlorofluorocarbons production should ultimately be cut to 15 percent of those levels or even phased out completely if there is to be no further damage to the ozone layer.

Since the late 1970s, the ozone layer, which forms naturally but is gradually depleted by the emissions, has contained a large hole over the South Pole. Tolba said the hole appeared slightly smaller this year than in 1987.