Updated June 15, 2015 7:05 p.m. ET
ROME—Pope Francis calls global warming a major threat to life on the planet, says it is due mainly to human activity, and describes the need to reduce the use of fossil fuels as an urgent matter, in a published draft of a much-awaited upcoming letter on the environment.
The draft copy of “Laudato Si’ ” (“Be praised”), his encyclical on the environment, has been eagerly awaited by business, policy makers and environmental groups. It was published online on Monday by the Italian magazine L’Espresso, three days ahead of its scheduled publication date.
The Vatican said the posted text wasn’t the final document, which would remain under embargo until Thursday, but it didn’t say whether there were material differences between the draft and the final document.
An encyclical is widely considered one of the highest forms of papal writing, intended to explain and elaborate Catholic teaching.
“Laudato Si’ ” is addressed not only to Catholics but to “every person who lives on this planet,” the pope wrote. In it, the pontiff related ecological concerns to his signature theme of economic justice, especially the gap in wealth between the global north and south.
In the draft, the pope wades into the debate over climate change, writing of a “very consistent scientific consensus that we are in the presence of an alarming warming of the climactic system.”
He writes that there is an “urgent and compelling” need for policies that reduce carbon emissions, among other ways, by “replacing fossil fuels and developing sources of renewable energy.”
While acknowledging that natural causes, including volcanic activity, play a role in climate change, the pope writes that “numerous scientific studies indicate that the greater part of global warming in recent decades is due to the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxide and others) emitted above all due to human activity.”
The encyclical has acquired outsized importance in recent months, given the moral suasion and the popularity of Argentina-born Pope Francis, the first pontiff from the developing world and one who has been particularly vocal in his advocacy of the poor and criticism of big business. Moreover, the encyclical comes at a time when governments, investors, industry executives and environmentalists are debating policy measures to address climate change.
The pope’s letter brings a new dimension to the wrangling over the issue. In 2013, a landmark United Nations report concluded that there was a 95% level of certainty that humans are responsible for most global warming and reiterated that a long-term planetary warming trend was expected to continue. The report said that air and oceans are getting warmer, ice and snow are less plentiful, and sea levels are rising. The U.N. report is believed to broadly reflect the views of most climate scientists.
Some other researchers, though, have remained skeptical about global warming and they remain unconvinced that human activity is the dominant cause.
Paul C. Knappenberger, a climate scientist with Cato Institute, a Libertarian think tank, said the pope “goes too far in the perception that the changing of the climate leads to bad outcomes and necessarily needs some sort of immediate reaction.”
Crucially, the pontiff’s words are expected to bolster the case of scientists and politicians who are seeking a global pact aimed at reducing greenhouse-gas emissions and potentially avoiding significant additional warming of the earth’s atmosphere and oceans.
The pope “is going to be reaching people that haven’t thought about this,” said Mindy Lubber, president of Ceres, a Boston-based nonprofit group that works with more than 100 companies with investments totaling $13 trillion to address climate risks to their business.
In December, nearly 200 countries are expected to meet in Paris and sign the new climate change agreement. Earlier this year, Pope Francis—who expressed disappointment at the failure of past international efforts to reach agreement on the issue—said that he aimed to publish the encyclical in time to affect the Paris meeting.
Sen. Edward Markey (D.-Mass.), one of Washington’s most vocal proponents of aggressive action on climate change, said the Pope’s encyclical “comes at a critical time as the world’s nations prepare to convene for international climate negotiations in Paris in December.”
The pope’s encyclical also comes as oil companies are turning increasingly vocal on climate change amid rising scrutiny from investors and governments. Many are looking to influence the debate by proposing remedies, including the imposition of a carbon tax, that might have a lesser impact on their business than more wide-ranging changes being sought by some.
Many of the industries’ largest players are advocating a shift away from coal to cleaner-burning gas—which they are producing in ever larger volumes—as a means to mitigate climate change while continuing to meet rising energy demand in the coming decades.
Earlier this year, Exxon Mobil Corp. sent a senior lobbyist to Rome in an attempt to brief the Vatican on its outlook for energy markets.
The American Petroleum Institute, a national trade organization that represents the U.S. oil and gas industry, including Exxon, said it was working to review the leaked document.
In laying out his thesis, the pope returned to his frequent criticisms of business, the problems of income inequality and the plight of poor countries.
The pope wrote that powerful economic and political interests seek to “mask the problems or hide the symptoms, seeking only to reduce the negative impacts of climate change.” But he warned that global warming could worsen “if we continue with the current models of production and consumption.”
Pope Francis also highlighted other environmental problems, including the depletion of clean water due to overconsumption and the loss of biodiversity.
“Water poverty” is especially acute in Africa and other poor regions, where poor water quality foments disease and shortages lead to rising food prices, the pope wrote.
Pope Francis emphasized the unequal social effects of environmental problems, which he said “strike in a special way the weakest on the planet.” Unequal access to natural resources has led to an “ecological deficit” between the northern and southern hemispheres, with the former exploiting the latter to the enrichment of its industrial economy, he wrote.
The 191-page document includes extensive sections on Catholic theology of creation, as well as critiques of economic globalization and consumer culture, which the pope argues have led to environmental degradation.
In terms of practical solutions, the Pope recognizes that poorer countries, which are typically dependent on fossil fuels, must put a priority on the “eradication of misery and the social development of their inhabitants.” In their transition to less polluting energy sources, such countries must count on the assistance of already developed countries, through subsidies and technology transfers, he writes.
The pope rejected population control as a solution to such inequities. “To blame demographic growth and not the extreme and selective consumption of some is a way of not facing the problem,” he wrote.
Part of the solution lies in adopting “another style of life,” featuring more environmentally conscious behavior, such as reducing use of paper, plastic and water; separating trash; car-sharing and turning off unnecessary lights, the pope wrote.
“One must not think that these efforts won’t change the world,” he wrote.
—Tammy Audiand Gautam Naik contributed to this article.