"I came to the conclusion a few years ago that the risk of climate change does exist and that the consequences of it could be serious enough that actions should be taken," the former Exxon Mobil CEO said at his Senate confirmation hearing.
Tillerson said the type of work that should be done on climate change is the largest subject of public debate, and the world's ability to predict the effects of greenhouse gas emissions is very limited.
He did not directly respond to a question as to whether human activity is causing climate change.
Trump said he would keep an open mind about climate change during a November interview with The New York Times. But he has made a number of statements, including during the Times interview, that cast doubt on climate change science and humans' role in global warming.
In 2012, Trump suggested on Twitter that climate change was a hoax created by the Chinese in order to make U.S. manufacturing less competitive. He later said the tweet was a joke, and during a debate with Hillary Clinton, denied ever having said it.
Tilllerson said he feels free to express his views to Trump on global climate change agreements. However, he noted that Trump has pushed an "America first" policy, suggesting U.S. participation in international climate pacts may be subject to considerations about their impact on American business.
"There is important considerations as we commit to such accords, and as those accords are executed over time. Are there any elements of that that put America at a disadvantage?" he said.
Trump threatened during the campaign to "cancel" the Paris Agreement, a pact among about 200 countries to take action to curb climate change. In the Times interview, he said he has an "open mind" on this issue, too.
Exxon Mobil, the world's most valuable publicly traded energy company, has been accused of misleading the public and investors on the risks of climate change. An investigation by Inside Climate News chronicled Exxon's research into climate change decades ago and its subsequent funding of efforts to block government action to curb fossil fuel emissions.
Tillerson declined on Wednesday to answer Democratic Sen. Tim Kaine's questions about whether Exxon misled the world about climate change.
Exxon has in recent years acknowledged the risks posed by climate change.
Surveys show the overwhelming majority of the scientific community believes humanity is the primary cause of global warming.