Pope Francis is taking on climate change in a leaked draft of a papal letter, known as an encyclical, to be published on Thursday, in which he couches climate change as a moral issue and one of wealth inequality.

The pope says wealthier countries have to help developing ones in dealing with the problem.

“Once the encyclical letter comes out, then priests all around the world are going to work it into their sermon,” says Andrew Hoffman, professor of sustainable enterprise at the University of Michigan.

“Right now, the primary messengers on climate change are democratic politicians, environmentalists and scientists. And we need more messengers from different domains,” Hoffman says. “The pope coming forward can make a moral argument where others can’t.”

The letter’s timing is important. About 200 countries plan to meet at the end of the year to sign a new climate change agreement. The pope wants to influence that process.

In his letter, the pope appears to be against carbon credits — a financial instrument that puts a price on air pollution. In his letter, the pope argues carbon credits could “give rise to a new form of speculation.”