AAP: Electricity prices will increase by 40 per cent by 2020 under economist Ross Garnaut’s greenhouse target. Professor Garnaut has recommended the nation cut emissions by 10 per cent in 12 years’ time, in his latest report. While a 40 per cent price increase would be a “big hit” for households, government revenue from emissions trading could compensate for that. Petrol would rise by five cents a litre in 2010 if it was included in the trading scheme as he …