Insufficient biofuels

This is closer to right than most pronouncements on it but it's still deeply wrong.

Climate Change Minister James Shaw said he supported the move, and he and Woods had now been tasked with quickly finding a way to fill the big hole in the budget.
“This is why we have a carbon budget right, is to say, when we make these choices, actually, we've got to plug the gap somewhere else,” he said.
"The most straightforward thing that we could do is to tighten up the ETS [emissions trading scheme] unit supply, so you simply take it out that way. But there may be other policy interventions that we could make as well.”

A biofuel mandate is neither necessary nor sufficient for a reduction in net national emissions. 

If you ran the mandate without cutting the cap, you'd just shift where emissions happen. If you ran the mandate while cutting the cap, you would reduce net emissions while also shifting where emissions happen. But it's the cutting of the cap that's both necessary and sufficient, all on its own. A biofuels mandate just shifts the location of emissions, regardless of whether you cut the cap.

So yeah, Shaw's right that you could cut the cap to reduce emissions. But there's no 'hole' created in anything by cutting a biofuels mandate. Compared to a counterfactual in which we'd have had a mandate, we get a few more emissions in transport, a few fewer emissions everywhere else, and a lower overall cost of getting down to net zero. 

Any 'hole' from not having a biofuels mandate is like the hole you make in a T-1000 if you shoot it. The thing fills itself in all on its own. More emissions in transport? There'll have to be fewer emissions somewhere else. That's how the ETS works. 

Want to stop T-1000? You don't do it by shooting at transport, or shooting at power generation. You do it by cutting the cap steadily over time to hit net zero.