Activist investor and newly appointed Exxon board member Jeff Ubben is building his stake in the company on the belief that the oil giant will be integral to the energy transition.

“I am,” he said Thursday on CNBC’s “Squawk on the Street” when asked if he was planning to buy more Exxon shares. “I am building this new business…I really believe that the return dynamics for Exxon from here are spectacular. They are part of the solution, not part of the problem,” he said.

Ubben, who is a proponent of ESG investing, joined Exxon’s board in March amid pressure from shareholders to reshuffle directors as the stock price languished.

ESG refers to a form of sustainable investing that centers on three factors: environmental, social and corporate governance.

Ubben is no stranger to investing in oil and gas companies. While at ValueAct, the firm he founded in 2000, he took a stake in BP, saying traditional energy companies can belong in ESG portfolios.

In recent months, Exxon has doubled down on its commitment to environmental goals as oil majors in the U.S. and abroad look to make their operations greener.

On Monday, the company proposed a $100 billion carbon capture project in Houston that would require the support of the industry and the government. In February, Exxon announced plans to invest $3 billion in carbon capture and other emissions-cutting technology.

Ubben noted that while net-zero power generation can be accomplished through renewable energy, Exxon’s size and scale makes it capable of tackling areas that are harder to decarbonize, including transportation and industrial activity.

“If you think about Exxon’s role, it’s to do the hard stuff, and you cannot get to net zero without doing the hard stuff,” he said. “To use the existing infrastructure and capture the carbon is probably the least expensive and quickest way to net zero,” he added.

Exxon’s emission-reduction targets have come under fire from those who say it’s too little too late. Engine No. 1, an activist group that’s been targeting Exxon since December, said the company hasn’t gone far enough in outlining its role in a zero-carbon world.

“We believe that reacting to the threat of a shareholder vote is not the same as a coherent and value-enhancing long-term strategy, and that without real change these gains could be short-lived,” the group said in March following Exxon’s investor day.

Still, Ubben said the company is working on “breakthrough technologies” supported by 20,000 scientists. He added that Exxon is the leader in the $2 trillion carbon capture business.

“This is the technology that will get us there quickest, and net-zero doesn’t happen without it,” he said.

Shares of Exxon were slightly lower on Thursday, but are up 35% this year.

– CNBC’s Kerry Caufield contributed reporting.