Probably not as controversial a question as others in this section but still needs careful arrangement of material for a strong argument, although beware of complacency.

The standard green organisations are a good starting point e.g. Greenpeace as is The World Bank and the more scientific organisations such as ESA, NASA (use the search function) and Cambridge University. It would be useful however to try and think wider including for instance biodiversity, agricultural and health impacts (a basic starting point) as well as damage to non-living material.

Be aware there may be a disparity between what is known, what we think is happening and what is happening, for instance see  EPA, UNEP, Alternet and Zarc International as well sites that dispute the actuality of ozone holes, http://members.aol.com/lindgren3/Ozone.html,http://www.fair.org/extra/best-of-extra/ozone.html and http://www.floodlight.org/theory/sub1.html.