The Vatican added yet another strange bedfellow to its expanding ecological alliance Wednesday, hosting anti-capitalist eco-crusader Naomi Klein at a conference on saving the planet.

Klein, author of "This Changes Everything: Capitalism vs. the Climate" and who has also supported a boycott of Israel for years, acknowledged Wednesday that, "as a secular Jewish feminist," she never expected to be invited to the Vatican.

But she told a Vatican news conference that Pope Francis' recent encyclical on the environment and the global economic system that is threatening it spoke to her. She said the manifesto should inspire those who use the Bible to defend human domination of nature and deny climate change to change their ways.

"Given the attacks that are coming from the Republican party around this and also the fossil fuel interests in the United States, it was a particularly courageous decision to invite me here," she said. "I think it indicates that the Holy See is not being intimidated, and knows that when you say powerful truths, you make some powerful enemies and that's part of what this is about."

The Vatican has come under fire from conservative Catholics for hosting the U.N. chief Ban Ki-moon and economist Jeffrey Sachs at another climate conference, given their support for universal access to contraception.

U.S. Republicans largely shrugged off Francis' encyclical, saying the pope should leave science to the scientists. And the conservative Catholic pro-free-market Acton Institute called the pope's manifesto "flawed" and "imprudent," given the role capitalism has had in lifting millions out of poverty.

Nevertheless, the Vatican is forging ahead to promote the encyclical and the science behind it, hosting Klein at its latest climate conference alongside Ottmar Edenhofer, co-chair of the U.N. Intergovernmental Panel on Climate Change, and gearing up for Pope Francis' trip to the U.S. in September, where he will press his climate agenda before Congress and the United Nations.

Klein, a Canadian author and activist, said that the critical state of the planet required unusual alliances to be formed to fight the fossil fuel interests blocking courageous action at U.N. climate conferences. That doesn't mean everyone agrees on everything or that one side's world view is "being subsumed by anyone else's," she said.

"This is an alliance on a specific issue. It's not a merger," Klein said. "But when you are faced with a crisis of this magnitude, people have to get out of their comfort zones."

In his encyclical, Francis called for a revolution to fix the "perverse" global economic system in which wealthy countries exploit the poor and pollute the Earth in the process.