"In other words, the Government has just committed to reducing less than 1 per cent of the country's emissions by 2025," Thunberg said in the tweet.
She also cited the "so-called climate emergency declaration," which passed in the House earlier this month.
Although she hadn't actually seen the tweet, Ardern said it had been described to her as a "reference to our public service carbon neutral goal of 2025."
That goal was announced last week, after she moved a motion to declare a climate change emergency in Parliament.
"If that was the sum ambition of any government, then it would be worthy of criticism," Ardern said of the tweet.
"It is not the totality of our plans on climate change. But again, I think that it's actually for us just to get on with the business of fulfilling our obligations and expectations."
Asked if that meant that Thunberg should have done a bit more research before her tweet, Ardern said no – "I'm not going to pass any judgment".
"But equally I think it's only a good thing [that] there are people out there continuing to urge ambition in action."
Asked about the tweet, Climate Change Minister James Shaw said Thunberg was essentially pointing out what the Government already knows.
"That we have a long way to go to narrow the gap between what our emissions are right now, and what they need to be in the future."
He said a climate change emergency declaration signals the Government's intent to do everything it can to tackle the climate crisis.
