UB scientists said they were expecting a "normal" ozone hole this year. Geir Braathen of the World Meteorological Organization said it's still too early to say for sure how big the ozone hole will be over Antarctica. He told journalists in Geneva on Friday that it will likely be smaller than the very large hole of 2006, but more pronounced than last year's relatively small hole. The hole has been forming since the mid-1980s in the extremely low temperatures that mark the end of Antarctic winter. Generally, the hole is biggest around late September. The hole is caused by thinning in the ozone layer largely due to chemical compounds leaked from refrigerators, air conditioners and other devices. It exposes the Earth to harmful solar rays.