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Pope Francis greets the pilgrims during his weekly general audience in St Peter's square at the Vatican on March 11, 2015.
© Giulio Napolitano/Shutterstock
19 June 2015 18:00

In-depth: the science behind the papal encyclical

Sophie Yeo


Sophie Yeo

19.06.2015 | 6:00pm
International policyIn-depth: the science behind the papal encyclical

Pope Francis attempted to start a global conversation yesterday with his new encyclical on the environment. Unlike most encyclicals, it was addressed not to Catholics, but to “every person living on this planet”.

There was one group, however, that received particular attention: scientists. For a select number, including climatologists, botanists, and oceanographers, the conversation began long before the Vatican presented its much-anticipated document in Rome yesterday.

Their influence can be found throughout the 184-page document, which some had speculated could be filled with theological obscurities rather than an empirical call to action on climate change.

They needn’t have worried. The apostolic exhortations and catechisms were relegated to second place behind the Pope’s concerns about melting ice caps, methane gas and carbon credits.


This content is the result of more than a year of consultation between Pope Francis and academics.

But the seeds of the idea were planted long before. Back in 1990, before the UN had set up a body dedicated to climate change, Pope John Paul II was urging Catholics to take care of their natural environment.

His successor, Pope Benedict XVI, was nicknamed the first “green pope” due to his exhortations to protect the natural world and his own efforts to cut carbon emissions, including purchasing carbon credits and installing solar panels, making the Vatican the first fully carbon neutral country.

Under his watch, the Pontifical Council for Justice and Peace released the “Ten Commandments of the Environment” in 2005, while another of its academic bodies held a workshop on the retreat of mountain glaciers in 2011.

Ottmar Edenhofer, chief economist at the Potsdam Institute for Climate Impact Research, says that a Vatican City project initiated under Benedict fed into the encyclical released yesterday. He tells Carbon Brief:

“We had, since 2010, three meetings in the Vatican City where we met with bishops from the Global South on climate change and climate change mitigation. This was something that was very important and interesting. We had been asked to provide inputs and those inputs have been used by the advisors of the Pope.”

This resulted in a book published in 2012, linking climate change, justice and sustainability.

Under Pope Francis, Edenhofer was called to the Vatican City in his capacity as co-chair of the Intergovernmental Panel on Climate Change (IPCC) report on mitigation – the third in the series of UN-backed compilations of the latest science released between 2013 and 2014. He says:

“I provided the input coming from the IPCC and they have used this input in a way that you can now find in the encyclical. This insight has been used by the writers of the encyclical.”

The Vatican itself has two scientific bodies, which have been involved more than any other in constructing the encyclical. These are the Pontifical Academy of Sciences and the Pontifical Academy of Social Sciences.

These two bodies contain academics from around the world, who are handpicked as life members, regardless of their religion. Their job is to produce reports on the science and report back to the Vatican’s hierarchy.

“They’re always recorded and the Pope directly or through his advisors looks at everything we conclude,” says Peter Raven, president emeritus of the Missouri Botanical Gardens, and member of the Pontifical Academy of Sciences since 1990, speaking to Carbon Brief.

In May 2014, the two bodies held a workshop covering a spectrum of climate change-related topics, from food production and the ocean to megacities and tropical forests. It was these discussions that prompted the writing of the encyclical “in earnest”, says Raven.

But Pope Francis has gone “several steps further” than his predecessors by highlighting the ethical dimensions of climate change, Raven adds. The encyclical is as much as scientific document as it is an appeal for global justice, rooted in care for the natural world. He says:

“I think that the Pope’s move away from the science and into moral responsibility is extremely important. Science doesn’t say you have to do anything about global warming, but it calls attention to the existence of global warming driven largely by human beings, and some of the potentially very negative impacts that could have.”

The scientific pope

Thanks to the personal involvement of Francis, who himself once worked as a chemist in Argentina, the scientists’ stamp appears throughout the document.

Cardinal Turkson, president of the Pontifical Council for Peace and Justice, wrote the first draft, with Francis steering it into its final shape, taking a week in March to finesse the final edition.

Along the way, he also met with scientists of the Pontifical Academy of Sciences so they could present their reports to him (“He’s every bit as charismatic and attractive and wonderful a person as implied,” says Raven).

The Vatican held another conference on 28 April this year, by which time the encyclical was largely finished, giving Francis and UN secretary general Ban Ki-moon an opportunity to converse about climate change on the sidelines, as well as gather more insight from scientists.

This is also where the Pontifical Academies released their own report, “Climate change and the common good: a statement of the problem and the demand for transformative solutions”, specifically designed to support Pope Francis’ work.

This process of consultation comes into fruition in paragraphs 23 and 24 of the encyclical. In precise language, free from the language of religion, Francis sets out the causes of climate change and its impacts.

Para -23-blue

Para -24-blue

Credit: Laudato Si, adapted by Carbon Brief.

This is not the only place where the Pope gets into the detail of climate change. He shows himself to be plugged into various topics, including, for example, the economy:

“The global economic crises have made painfully obvious the detrimental effects of disregarding our common destiny, which cannot exclude those who come after us.”

Renewable energy:

“Taking advantage of abundant solar energy will require the establishment of mechanisms and subsidies which allow developing countries access to technology transfer, technical assistance and financial resources.”

International policy:

“Enforceable international agreements are urgently needed, since local authorities are not always capable of effective intervention.”

And the fossil fuel industry:

“We know that technology based on the use of highly polluting fossil fuels – especially coal, but also oil and, to a lesser degree, gas – needs to be progressively replaced without delay.”

Scientific input

None of the scientists involved in the process approached by Carbon Brief could point to exactly how or where their input was incorporated. Astronomer Royal Professor Martin Rees, appointed to the Pontifical Academy of Sciences in 1990, tells Carbon Brief:

“The Vatican’s a diverse and mysterious place, and I’m sure there were lots of other influences and discussions that I wouldn’t be aware of.”

Yet the similarity between the encyclical and the supporting information produced by the scientists is evident.

The statement produced by scientists and economists at the May 2014 meeting speaks about the “technological and operational bases” for sustainable development and focuses on the “growing gap between the rich and the poor within and between nations”. Like the encyclical, it looks at the impact of industrial agriculture on ecosystems.

Meanwhile, the report of the Pontifical Academies called for “near-zero carbon emissions by around 2070”, which would mean rapidly replacing fossil fuels with renewable energy, as the Pope recommends – although there was some ambiguity about this demand, and the precise wording is not repeated in the encyclical.

At the request of the Vatican, Professor Hans Joachim Schellnhuber, the director of the Potsdam Institute, who was also heavily involved in the scientific background to the encyclical, wrote a report to accompany its release.

The institute tells Carbon Brief that it represents a “compilation” of his scientific work and thinking on climate change. It covers topics such as possible solutions to the problem, and the graduated impacts of failing to prevent it, as the graph below shows.

Graph showing the temperature at which climatic "tipping points" set in

Graph showing the temperature at which climatic “tipping points” set in. Blue/grey line shows temperature so far, with Representative Concentration Pathways (RCPs) indicating scenarios based on future emissions levels. Source: Common Ground, Hans Joachim Schellnhuber.

Global commons

But the most important element of the encyclical is where science and morality merge in the presentation of the atmosphere as a “global commons”, says Edenhofer.

In paragraph 174, the Pope writes:

“What is needed, in effect, is an agreement on systems of governance for the whole range of so-called ‘global commons.'”

As shown in the text box above, this would mean treating the atmosphere as the common property of mankind and regulating it accordingly, rather than allowing it to be freely accessible to whoever wants to, without penalty, pollute it. Edenhofer says:

“It seems to be me that the most fundamental and revolutionary sentence in the encyclical is number 23, where it says climate is a global commons, which means a global commons for all and by all human beings.
“This is something that is very much related to the social teaching of the Catholic church, because it has always argued that private property has a kind of social mortgage, which means the private property of fossil fuels has to be be regulated in a way which is consistent with the limiting disposal space of the atmosphere.”

Schellnhuber’s report to support the encyclical examines the scientific and policy implications of turning the atmosphere into a “global commons”. He says:

“The atmosphere is a global good because of its limited disposal space for greenhouse gas emissions. Presently, the upper-middle classes worldwide are rapidly depleting this scarce resource by emitting greenhouse gases in vast amounts. In contrast to the limited disposal space in the atmosphere, fossil fuels, especially coal, are abundant. Hence limiting the increase of global mean temperature to 2C requires confining the amount of carbon still to be released into the atmosphere to 1000 gigatons of CO2 (or less).
“Whereas restricting the use of the atmosphere as a carbon dump is absolutely necessary to avoid intolerable damage and suffering for the many, it will devalue the assets and the property titles of today’s owners of coal, oil and gas. Almost 80% of coal has to remain underground in a climate-change mitigation scenario compared to a business-as-usual case. Hence, climate policy implies shifting property rights for using the atmosphere from fossil fuel owners to a novel owner – humankind as a whole.”

Limits of science

The encyclical is a case of the Pope doing what science cannot.

Last year in Berlin, government representative met to approve, line-by-line, the “ summary for policymakers” of the IPCC’s working group 3 report. As co-chair, Edenhofer watched on as delegates from countries as diverse as the US, Tanzania, Canada, South Sudan and France objected to the inclusion of the phase “global commons” in the IPCC’s summary document, which is forwarded to governments around the world.

Their concern was that this could be seen as a political statement in what is supposed to be a policy-neutral document. The idea of the “global commons” was eventually relegated to a footnote, which stresses that it “has no specific implications for legal arrangements”.

According to Raven, the genesis of the encyclical lay in the frustration of scientists about the near-stagnant efforts to tackle climate change, compared to the urgency of their own research. This is what makes the encyclical even more powerful than the IPCC, he tells Carbon Brief.

“I think the scientific community felt rather stranded with the need for action and the relative inability of science itself to generate that action – and now we have a real call for action, which comes from a morally highly placed and very authoritative source.”

The fact that the Pope has done a “pretty balanced job” of incorporating the input of scientists reinforces the authority of the encyclical, says astronomer Rees. He tells Carbon Brief:

“There are a lot of uncertainties and the main point is to adopt a balanced view and to accept that we need to pay an insurance premium against a worst case.”

Partha Dasgupta, emeritus professor at the University of Cambridge, who has been a key player in the scientific events leading up to the encyclical, praised the Pope’s treatment of economics. He tells Carbon Brief:

“His treatment of economics is expert. What he adds to the subject is the appeal to not treat Nature altogether like the commodities that appear in economics textbooks. Relying entirely on getting the price of natural capital right is a mistake, or so I interpret him to be saying, and I am convinced he is right about that.
“I read him as saying that ultimately we have to relate differently to Nature, regard it as part of ourselves, otherwise we will mistreat it, to our detriment, and he is right about that, too.”

However, Edenhofer stresses that “we should not perceive this encyclical as a kind of substitute for an IPCC document”. He says it is “complementary”, adding:

“It is not a document which wants to prescribe the international negotiations. The Pope wants to highlight, focus and emphasise fundamental ethical principles…In the IPCC, we said something on ethics, but not too much. Science is very limited in its capacity to emphasis ethical principles. This is his role. But in this role he wants to avoid being too precise.
“I would say that we should not read this encyclical as a climate encyclical. It’s an encyclical about climate change, poverty, inequality and justice and he wants to point the decision-makers towards what kind of ethical principles are important to address. Like the protection of the poor. Like the global commons. Like the universal destination of goods. And like intergenerational justice. Therefore, he does not want to be too specific and just replicate what the IPCC and the UNFCCC have said [about carbon budgets and the 2C goal].”


In Paris this December, world leaders will meet to sign a new UN treaty aimed at regulating greenhouse gas emissions and dealing with the impacts of climate change.

From discussions to date, it seems likely that much of the debate will centre around how much each country should rein in its emissions, essentially making a personal effort for the global good.

The conversation may have started in the language of science, but the morality of the message will be heard across all the countries of the world, including the diplomats on whom the burden of action now falls.

With 1.2 billion Catholics in the world, the Pope’s message is expected to reverberate far beyond the Vatican (which doesn’t count as a country at the UN). Raven says:

“What I hope the document will do is call people’s attention to the severity of the problem, and encourage them to move forward rather than sitting around talking past each other in a polyglot Tower of Babel situation.”
Main image: Pope Francis greets the pilgrims during his weekly general audience in St Peter’s square at the Vatican on March 11, 2015. 
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