Donald Trump's nominee for Secretary of State, Rex Tillerson, expressed opposition to several of the president-elect's foreign policy proposals during his confirmation hearing Wednesday, saying he disagrees with the call for a new nuclear arms race — but isn't necessarily opposed to a creating a registry of Muslims in the U.S.AP/Evan Vucci - apimages.com

Here are three issues where Tillerson and Trump don't see eye-to-eye.

1. Climate change

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Trump has characterized man-made climate change as "a hoax" intended to "justify higher taxes." Though he recently conceded "there is some connectivity" between human activity and global warming — and walked back a pledge to abandon the Paris Climate Agreement — Tillerson's stance on the issue starkly contrasts with  the president elect's.

"I came to the decision a few years ago that the risk of climate change does exist and the consequences could be serious enough that it warrants action," Tillerson, the CEO of oil giant ExxonMobil, told senators Wednesday. "The increase in greenhouse gases in the atmosphere are having an effect. Our ability to predict that effect is very limited."

2. Russia

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Trump has faced criticism over his avowed fondness for Vladimir Putin, with Tillerson himself having come under fire for his businesses dealings with the Russian president. But at the nominee's hearing, Tillerson described Russia's 2014 invasion of Ukraine as an "illegal action" and said it was a "fair assumption" Putin authorized cyber attacks against the U.S. Trump, by contrast, has declined to condemn Russian intervention in Ukraine, but on Wednesday finally said he thought Russia was behind hacks on the Democratic National Committee.

"Russia must know that we will be accountable to our commitments and those of our allies, and that Russia must be held to account for its actions," Tillerson said.

Tillerson stopped short of calling Putin a "war criminal" over Russia's intervention in Syria. "Those are very, very serious charges to make, and I would want to have much more information before reaching a conclusion," Tillerson said when pressed by Florida Sen. Marco Rubio.

3. Nuclear weapons

In December, Trump tweeted that the U.S. "must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes." He followed up by endorsing the idea of a nuclear arms race in an interview on MSNBC’s Morning Joe, raising alarm among nuclear policy experts.

When Massachusetts Sen. Ed Markey asked if he agreed with the president-elect, Tillerson responded: "I don't think anyone advocates for more nuclear weapons on the planet," adding "I do not agree" with Trump's suggestion the U.S. should expand its capacity.

"One of the vital roles for the State Department to play has to be the pursuit of nuclear nonproliferation," Tillerson said. "We just simply cannot back away from our commitment to see a reduction in the number of these weapons on the planet."

But it wasn't all disagreement, with Tillerson declining to rule out the creation of a national registry to track Muslims living in the U.S.

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Tillerson told senators that while he didn't support a ban on immigration to the U.S. based solely on religion, he wasn't in a position to necessarily oppose putting Muslims in a national database, as proposed by the president-elect. He said he "would need to have a lot more information around how such an approach would even be constructed," and specified that such a registry would include other groups "that are threats to the U.S.," not just followers of Islam.

One reason Trump and his nominee appeared to disagree on some foreign policy matters is Tillerson was facing a tough audience, one more critical of Russia than his prospective boss. Tillerson also admitted that the two haven't discussed world affairs at length since he was nominated, nor have they "yet" had any conversations on Russia in particular.