In June, Pope Francis made headlines when he challenged the world to take action against climate change and other environmental ills.

Those who deny the scientific evidence that humans pose a threat to the climate were not amused, and on Thursday, a week before the pontiff arrives in Philadelphia, some of them struck back.

Representatives from the Heartland Institute, a conservative Chicago-based think tank, joined the local Independence Hall Foundation and other advocates in railing against what one them called "eco-zealots."

They spoke in a conference room at the Independence Visitor Center, a location picked for its significance. The speakers view the pope's message as tantamount to an anticapitalist infringement on U.S. independence and sovereignty. Foreigners should not be telling Americans to spend money on curbing emissions, they said.

"This is about taxation without representation," said Elizabeth Yore, an attorney known for fighting child abuse and human trafficking.

Gene Koprowski, Heartland's marketing director, said he and colleagues initially thought the pope had spoken about climate change because he was getting "bad advice." They now think he is inspired in part by "pagan remnants" of "nature worship" that have crept into the church, he said.

"I think we're seeing the revelation of an animistic form in the church," Koprowski said.

Whatever his motives, Francis is in lockstep with the scientific consensus.

Average global surface temperatures have risen about 1.5 degrees Fahrenheit since 1800, according to the Intergovernmental Panel on Climate Change, the global research group with ties to the United Nations. Scientists project that if the world does not restrict emissions of heat-trapping greenhouse gases, temperatures will rise an additional 4.7 to 8.6 degrees by century's end.

The rising temperatures have contributed to sea-level rise and are expected to lead to heat waves and droughts, crippling poor nations without the resources to adapt, climate scientists generally agree.

Jay H. Lehr, the Heartland's science director and a hydrologist, sought to poke holes in the science Thursday. Among other points, he said any human impact on the climate is dwarfed by natural variability in temperatures throughout Earth's history.

Going back millions of years, that is true, but climate scientists are in near-universal agreement that human activity is the dominant factor in the temperature increase since the beginning of industrial times.

Late in the hour-long event, attended by several reporters and a handful of onlookers, an environmental activist stood up and angrily likened the climate skeptics to Holocaust deniers. WPHT radio host Dom Giordano, who was present in support of Heartland, engaged her in a spirited argument, with neither side conceding.

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