Leaders of the world’s most powerful companies sent one clear message this week as they gathered in this ski chalet town for the World Economic Forum: They care about the environment — to a point. With the Australian bush fires raging and teen activist Greta Thunberg proclaiming that “our house is still on fire,” business leaders were eager to talk about how they are eliminating plastic water bottles at their headquarters, installing solar panels on their homes and corporate buildings, and planting a lot of trees.

Nearly everyone attending the Davos events committed to join the new “1 trillion tree” initiative to plant an abundance of trees by 2030. Even President Trump signed on, despite his insistence that “prophets of doom” about climate change are wrong. But conversations grew tense when it came to putting a price on carbon. “If you want to put a tax on people, go ahead and put a carbon tax. That is a tax on hard-working people,” U.S. Treasury Secretary Steven Mnuchin said on a panel Friday. He argued that a tax was unnecessary because technology would almost certainly bring down clean-energy costs.

Economists across the political spectrum overwhelmingly say the best way to tackle climate change is to enact a carbon tax or a “cap-and-trade” system, in which there’s a limit on carbon emissions and companies that go past it must purchase credits. But at the World Economic Forum, the idea is still a somewhat dicey subject, at least among chief executives and government leaders from certain parts of the world. “I was in a few discussions where we talked about the price of carbon. That’s definitely something there is no agreement on,” Douglas Peterson, chief executive of financial firm S&P Global, said in an interview on the sidelines of the forum. Few chief executives are brave enough to publicly say they are against a carbon tax. They are fearful of the 17-year-old Thunberg and her allies calling them out on Twitter or in speeches.