Carbon tax and the collapse of gas prices: a failure for pigovian taxes?

Why carbon taxes will not work in this setting.
"Look at it this way. A study by Michael Greenstone and Thomas Covert of the University of Chicago and Professor Knittel concluded that at current battery prices, for an electric vehicle to be cheaper to run than a gas-power car, oil would have to cost $350 a barrel. Last year, it averaged $50. To make up the difference would require a carbon tax of $700 a ton of carbon dioxide."

http://www.nytimes.com/2016/03/02/business/does-a-carbon-tax-work-ask-british-columbia.html?smid=pl-share&_r=0