What is a carbon price; is it effective and efficient?

A carbon pricing scheme operated in Australia between
1 July 2012 and 1 July 2014, at $23 per tonne of carbon
dioxide equivalent emitted. Over the two years of the
scheme’s operation, output from brown coal fred generators
declined by 16 per cent (with plant use dropping from
85 per cent to 75 per cent), and output from black coal
generators declined by 9 per cent. Coal generation’s market
share fell to an historical low of 73.6 per cent of NEM output
in 2013–14.
Overall, these changes contributed to the emissions
intensity of NEM generation falling by 4.7 per cent. This fall,
combined with lower NEM demand, led to a 10.3 per cent
fall in emissions from electricity generation over the two
years that carbon pricing was in place
The repeal of carbon pricing from 1 July 2014 led to some
coal plant being returned to service, and to a signifcant
fall in hydro generation output. This shift contributed to a
4.3 per cent rise in electricity emissions in the NEM in the
year to 30 June 2015.

The Australian Government in 2014 replaced carbon
pricing with a Direct Action plan to achieve Australia’s
2020 emissions reduction target. Central to the plan is an
Emissions Reduction Fund that provides funding for the
Clean Energy Regulator to purchase emissions reductions at
the lowest available cost through competitive auctions.
The majority of abatement from the two auctions held in
2015 is via sequestration projects that trap carbon through
measures such as planting trees and storing carbon in soil;
landfll and waste related projects; and bushfre prevention
through savannah burning. No electricity generation projects
participated in the 2015 auctions.