Unit 2: Government action: Australia to ban incandescent lightbulbs

These articles from AP (document) and the BBC (clip) explains the Australian government's action

http://hosted.ap.org/dynamic/stories/B/BAN_THE_BULB?SITE=1010WINS&SECTION=HOME&TEMPLATE=DEFAULT

< http://www.bbc.co.uk/mediaselector/check/player/nol/newsid_6380000/newsid_6383000?redirect=6383053.stm&news=1&nbwm=1&bbram=1&bbwm=1&nbram=1 >

a) What is the negative externality?
b) What type of action is the government taking to reduce the negative externality?
c) How significant an action is this by the government in terms of global warming?