SIR – Malcolm Wood may well be right about swine flu (Letters, January 15), but he is quite wrong about the hole in the ozone layer as it’s only now repairing itself because we are leaving it alone.

It was in great danger of being destroyed by chlorine from industrially manufactured HCFC and CFC chemicals used in refrigeration and fire extinguishers.

Once the cause was recognised, we demonstrated an impressive ability to work together on an international level and the Montreal Protocol, 1987, banned these rogue chemicals and gave the protective shield of the ozone layer a chance.

There is a lesson here about carbon dioxide and global warming.

Keith Thomson, Heights Lane, Bradford