The dominant issues at Wednesday’s hearing on the nomination of Rex Tillerson, the former chief executive of Exxon Mobil, for secretary of state are likely to be Mr. Tillerson’s ties to Russian president Vladimir Putin and any potential conflicts of interest arising from Exxon’s extensive global operations. But members of the Senate Foreign Relations Committee will be sadly delinquent if they do not press him on the issue of climate change.

Mr. Tillerson, who concedes that climate change is a problem, has been seen as a bright spot in the bleak lineup of climate deniers that Donald Trump has named to other cabinet positions. But that’s a very low bar, and if Mr. Tillerson has any hope of raising the issue to the prominence it deserves, and changing the mind of a president-elect who has already called global warming a “hoax,” he will have to be tough and tenacious. And he won’t be unless he really cares.

It will fall to the committee’s Democrats — in particular people like Ed Markey of Massachusetts and Tom Udall of New Mexico — to try to find out whether he does, for at least two reasons. One is that the secretary of state will be pivotal in maintaining America’s leadership role in the worldwide effort to reduce greenhouse gases — an effort that reached an important milestone in the global agreement in Paris a little over a year ago when 195 countries agreed to join in keeping global temperature increases below dangerous levels. That agreement would not have been possible without the extraordinary diplomatic labors of John Kerry, the person Mr. Tillerson is nominated to replace, and also a person who saw climate change as a supremely important issue and put it near the top of his agenda.

The second reason to gauge the level of Mr. Tillerson’s interest is that he is a career employee of an industry whose main products, oil and natural gas, contribute mightily to global carbon emissions and whose interest in regulating those emissions has been close to zero.