Understanding Climate Change "tipping points'

Someone said to me earlier today that they wanted a 'brief something' on tipping points of climate change - coincidently I was able to point them to this short film - a little grim but very real and positive stuff too:
wakeupfreakout.org/film/tipping.html
I also found recently Dr Lawson's 500 words on the evidence that Global warming is actually happening now:
www.greenhealth.org.uk/AGWEvidence.htm
Also see the recent article re climate change in The Guardian:
www.guardian.co.uk/environment/2008/aug/01/climatechange.carbonemissions