Pope Francis argues that climate change will put an outsized burden on the world's poorest people. Credit: Franco Origlia/Getty

Climate change is a major threat to the planet, Pope Francis warns in a leaked draft of an eagerly awaited statement on the environment. Left unchecked, global warming could lead to “an unprecedented destruction of ecosystems, with grave consequences for all of us”, he says in the document, which was published on 15 June in the Italian magazine L’Espresso.

The Pope’s 192-page statement, known as an encyclical, is due to be released officially on 18 June. Entitled Laudato si' (Praised Be), it is aimed at Catholics and non-Catholics alike. In it, Francis berates political leaders for failing to combat climate change, arguing that “the humanity of the post-industrial period may be remembered as one of the most irresponsible in history”.

Although he is not the first pope to discuss the world's environmental problems, Francis has done so more regularly — and in stronger terms — than have his predecessors. In January, he said that humanity had “slapped nature in the face”. And he has timed his encyclical to raise awareness about climate change before nations meet at a UN conference in December to negotiate limits on greenhouse-gas emissions. Francis will also discuss environmental issues in a speech to the UN General Assembly this September.

Such actions have drawn criticism from conservative Catholics, but this does not seem to have changed the Pope’s position.

There is “very substantial scientific consensus that indicates that we are in the presence of a worrying warming of the climate system”, Francis writes in the draft. The bulk of the warming that has been observed over the past few decades is a result of greenhouse gases produced by human activities, the Pope adds, citing “numerous scientific studies”.

With this in mind, the Pope calls for urgent reductions in heat-trapping emissions to avoid dangerous impacts such as rising sea levels and melting ice caps. Replacing fossil fuels with renewable-energy sources is a start, Francis says, but such technical fixes must be complemented by a shift in attitudes.

Richer nations must shoulder the greatest responsibility for dealing with climate change, he says, ensuring that its negative effects do not fall disproportionately on poor people and on future generations.

Government guilt

The Pope saves some of his sharpest criticism for politicians. Although they have negotiated some successful environmental deals, such as the 1989 Montreal Protocol to protect the ozone layer, progress in limiting greenhouse-gas emissions has been “woefully poor”, Francis says. A landmark UN conference on sustainable development in Rio de Janeiro in 2012 produced a final declaration that was “as wide-ranging as it was ineffective”, he adds.

Still, Francis says that the Vatican should refrain from promoting specific policies to address the climate problem — and seek instead to encourage “honest scientific debate”.

The idea that rich nations have a special duty to fight climate change does not sit well with Paul Knappenberger, who is the assistant director of the Center for the Study of Science at the Cato Institute, a free-market think tank in Washington DC. He says that the encyclical lays too much blame on the West, and argues that access to technology, fertilizer and appropriate crop varieties has a bigger influence on food production in poor countries than climate change does. “There are plenty of more-effective things you can do to help the world besides trying to change the climate,” Knappenberger says.

But James Bretzke, a Catholic theologian at Boston College in Massachusetts, says that the Pope's encyclical outlines a moderate position that is in tune with mainstream climate science. This is not surprising, he adds, but it may discomfit those who are sceptical of a human influence on Earth's climate — such as the US Republican politician Rick Santorum, a Catholic who said recently that the Vatican should concern itself with moral, rather than scientific, issues.

That is at odds with the position that the Pope has taken: in both his encyclical and in public statements, he has repeatedly sought to frame climate change as a moral issue.