What Did Actual Scientists Think Of The Pope’s Climate Encyclical?


The Vatican’s new encyclical is being hailed as one of the most important statements on climate change ever produced by the Catholic Church. But it’s also being decried as misplaced, by some who say Pope Francis — a man of faith — has no business discussing matters of science.

“The church has gotten it wrong a few times on science,” said Catholic GOP presidential candidate Rick Santorum earlier this month. “We probably are better off leaving science to the scientists, and focusing on what we’re really good at, which is theology and morality.”

Pope Francis’ encyclical — titled “Laudato Si,” or “Praised Be” — does primarily focus on the moral reasons for acting on human-caused climate change. Those reasons, however, are based on the science of climate change, which the document discusses in surprising detail.

So, the obvious question is: has the church “gotten it wrong” on science again?

ThinkProgress asked three climate scientists to weigh in on three specific passages in the encyclical that get wonky about the science of climate change, and got varied answers. However, all three said Francis (who himself has a technician’s degree in chemistry) was correct that humans are causing potentially catastrophic climate change via greenhouse gas emissions.


“Based on what I have seen of the science in the encyclical, most climate experts would find little to disagree with,” said Anthony Broccoli, a professor of environmental sciences at Rutgers University.

In passages 23, 24, and 25 of the encyclical, Francis discusses the science of climate change at length. “A very solid scientific consensus indicates that we are presently witnessing a disturbing warming of the climatic system,” it reads. “[A] number of scientific studies indicate that most global warming in recent decades is due to the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxides and others) released mainly as a result of human activity. Concentrated in the atmosphere, these gases do not allow the warmth of the sun’s rays reflected by the earth to be dispersed in space.”

Those statements were accurate, except for one small thing, according to Deborah Huntzinger, an assistant professor of climate sciences at Northern Arizona University. Huntzinger said the only technical “error” she noticed in the passages was the pope’s explanation that greenhouse gases cause global warming by “prevent[ing] the heat of the solar rays reflected from the Earth to be dispersed in space.”

Technically, Huntzinger said, the way greenhouse gases warm the planet is a bit more complicated. Yes, she said, incoming solar radiation is reflected by the atmosphere, but the rest is absorbed by Earth’s surface. And as the Earth absorbs that solar radiation, it also warms. That warmed surface then emits and radiates more thermal energy, and the greenhouse gases in the atmosphere absorb it.

“So technically, greenhouse gases are not preventing solar rays reflected from the Earth to be dispersed in space, they are absorbing and re-emitting longwave radiation emitted from Earth’s surface,” she said. “The result is that the surface of the Earth and lower atmosphere are warmer than they would be if no GHGs were present.”

CREDIT: Oxford University
CREDIT: Oxford University

So it may be safe to say the pope’s explanation of the greenhouse effect was not as robust as some scientists may have liked. In all though, Huntzinger said, “the pope captures the science quite well.”


Michael Mann, director of the Earth System Science Center at Pennsylvania State University, agreed that the encyclical had strong scientific language. A portion of passage 24 reads as follows:

Warming has effects on the carbon cycle. It creates a vicious circle which aggravates the situation even more, affecting the availability of essential resources like drinking water, energy and agricultural production in warmer regions, and leading to the extinction of part of the planet’s biodiversity. The melting in the polar ice caps and in high altitude plains can lead to the dangerous release of methane gas, while the decomposition of frozen organic material can further increase the emission of carbon dioxide. Things are made worse by the loss of tropical forests which would otherwise help to mitigate climate change. Carbon dioxide pollution increases the acidification of the oceans and compromises the marine food chain.

“Everything he’s stated [above] accurately reflects what the science has to say,” Mann said in an email.

However, Mann noted his own problem with the scientific language. “If anything, Pope Francis is overly conservative [with respect to] the science in the encyclical,” he said.

According to Mann, a few things were understated. For example, the document stated warming was due to carbon emissions “released mainly as a result of human activity.”

“All of the increase in the carbon dioxide is due to fossil fuel burning and other human activities,” he said.

In all, though, all the climate scientists ThinkProgress consulted with said Pope Francis had done well at evaluating the state of climate science today, even though he’s not a scientist. However, according to Rutgers’ Anthony Broccoli, that shouldn’t be a surprise.


“Pope Francis doesn’t have to be a scientist to arrive at these conclusions,” he said. “All he would have to do is consult the extensive reports on climate change that have been written by the world’s climate scientists in a process organized by the Intergovernmental Panel on Climate Change. These reports have been written to inform policymakers and stakeholders about the state of the science and they are a reliable source of information.”


This post has been updated to include a mention of Pope Francis’ science background.