Mary Lou-McDonald "doesn't believe her own rubbish" when it comes to climate change the Taoiseach has claimed in the Dáil.
Leo Varadkar has told the Dáil that carbon taxes will be necessary to tackle climate change and went on to attack the Sinn Féin leader stating she is "not being honest" and "is not really on the side of the environment".
Under questioning from Ms McDonald on the introduction of a carbon tax, Mr Varadkar said: "I have no doubt Sinn Féin will do what it always does, which is the populist thing to peddle solutions that don't add up."
Ms McDonald described climate change as the "defining challenge of our generation" and said we are already "way, way behind" where we need to be in effectively tackling the issue.
However, she said the way to address climate change should not be through increasing the cost of living for low and middle-income workers.
She said a carbon tax would be a punitive measure which must be opposed.
Responding, Mr Varadkar said Sinn Féin "never let the facts get tin the way of a good political charge".
The deputy sounds to me like one of the hard Brexiteers across the water, we know what she is against but we don't know what she is for.
"If you think we are going to respond to those young people who want us to get our act together on climate change by only doing things that are popular, by only doing investments, by only handing out grants, I don't think you believe your own rubbish."
He added: "Carbon tax will not solve the problem of climate change but we will not solve the problem of climate change without carbon tax, it is and has to be part of the solution."
Mr Varadkar said the whole point of a carbon tax is to encourage people and large corporations to change their behaviour.
But he ruled out a four-fold increase in the next Budget and said "if there is an increase in the carbon tax it is my strong view that the money should be ring-fenced and given back to people in the form of increasing the fuel allowance to protect those who are least well off, in the form of tax credits, in the form of a dividend model."