Elon Musk is a well-known clean energy advocate – but he shocked many followers this week when he threw his support behind former ExxonMobil CEO Rex Tillerson as Secretary of State. Acknowledging his support could be startling, Musk took to Twitter to say the oil mogul actually “supports a carbon tax.”

The Economist tweeted a December 2016 article titled “Give Rex a chance” on the occasion of Tillerson’s narrow approval as Secretary of State. Musk responded to the article, saying “This may sound surprising coming from me, but I agree with The Economist. Rex Tillerson has the potential to be an excellent Sec of State.”

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Related: Rex Tillerson says Trump is wrong about climate change

Naturally Musk followers were quick to ask him why he’d support Tillerson, and he said, “Rex is an exceptionally competent executive, understands geopolitics and knows how to win for his team. His team is now the USA. I share The Economist’s opinion that he should be given the benefit of the doubt unless his actions prove otherwise.”

Musk also pointed to statements from Tillerson’s confirmation hearing where Tillerson said the United States should “maintain its seat at the table in the conversation on how to address threats of climate change. They do require a global response.”

Several hours after he sparked the conversation Musk tweeted, “Rex Tillerson supports a carbon tax. This is what is really needed to move the needle.” He included a link to a December 2016 Bloomberg article, which back then noted Musk and Tillerson agreed on a carbon tax as the “best tool for fighting climate change.”

It remains to be seen if Musk’s backing will be justified and if Tillerson will follow through on a carbon tax.

Images via NASA Kennedy on Flickr and Archive of the Official Site of the 2008-2012 Prime Minister of the Russian Federation Vladimir Putin