Thunberg, who was selected as Time's Person of the Year for 2019, has returned to the World Economic Forum's annual summit in Davos, Switzerland, this week to press her call for businesses, world leaders and others to take action in the face of scientific evidence showing that temperatures on Earth are rising.
The US, Mnuchin said, has been a leader in reducing carbon emissions.
And just two days later, Mnuchin's own wife appeared to take Thunberg's side. "If you DO have one, as I do, they'll claim it's illegitimate".
Speaking at the same event on Saturday, economist Jim O'Neill, a former Goldman Sachs chief economist, noted Mnuchin's choice of the word stable rather than the more traditional reference by US treasury secretaries to their support for a strong dollar.
Mr Mnuchin, who met Mr Javid for breakfast on Saturday morning and posted an image of them on Instagram, said the USA was "prepared to dedicate a lot of resources" to securing a trade deal with the United Kingdom this year.
"I support a stable dollar but I'm not going to make more comments on that", he said at an event held at the Chatham House think tank in London.
"If we can push companies into the direction of actually anticipating the transition, pricing it, and making sure that they move to cleaner and cleaner energy uses, then it helps", she said.
Thunberg, a teenager on the autism spectrum, has risen to global prominence on environmental issues in recent years after completing a transatlantic voyage to attend conferences on climate change in New York City.
"We are being criticized like that all the time", Thunberg said at the news conference onstage with four other campaigners.
Linton has kept a relatively low profile since a controversy in 2017 where she apologized after a sustained backlash for a now-deleted Instagram post touting her wealth and her subsequent response belittling a commentator. "Now chilling and watching a good old fashioned movie with a friend".
In a speech on Tuesday, Trump castigated the "prophets of doom" and those that predicted a climate "apocalypse", while Thunberg sat in the audience.
"Do we want to go down in history as the people who did nothing to bring the world back from the brink, in trying to restore the balance, when we could have done?"
"If we cared about that, we would not be able to do what we do".