United Nations Secretary-General Kofi Annan has called for greater efforts to save the world's radiation-shielding ozone layer. 

In a message marking the International Day for the Preservation of the Ozone Layer, Annan warned that the ozone layer remains depleted above the Antarctic and the Arctic, as well as in the midlatitudes of both hemispheres of the earth.

He said several challenges remained to be met. Developing countries must phase out the use of many ozone depleting substances within specified time schedules, and more research is required on the relationship between depletion of the ozone layer and climate change. 

Skin cancers kill 66,000 people each year, much of it due to the sun's ultraviolet radiation.