The encyclical of Pope Francis on climate change and many related themes, long surrounded by controversy and leaked to the press on the eve of publication, was formally released by the Vatican on 18 June 2015. The final version, hardly changed from the one seen earlier, places much emphasis on human responsibility both for climate disruption and for wider ecological damage.

Laudato Si (“be praised”), On the Care of Our Common Home, is in the tradition of a small number of noted encyclicals dealing with issues far beyond the internal evolution of church thinking. In its desire to highlight (as one report says) "the threat that a warming planet, rising sea levels and more extreme storms pose to his community’s poorest and most vulnerable”, it is widely seen as a progressive document from a pope who, in his previous life as an Argentine cardinal, was considered a conservative on most issues.

There are two earlier examples of unusually forthright encyclicals. The first was Rerum Novarum (“of revolutionary change”), Rights and Duties of Capital and Labour, which came from Pope Leo XIII in May 1891. It was prompted by the degraded state of working people in many industrialising countries, and largely concerned with economic issues. The document was progressive only in parts, and supported the right to private property; but in noting the duties of employers and the rights of labour to organise, it became known as the “workers’ charter”. Such points may seem mild now but in their day provoked not a little anger among ruling elites.

The second example arrived more than seventy years later, in April 1963. This was Pacem in Terris (“peace on earth”), from the elderly but surprisingly progressive Pope John XXIII. The main focus was on human rights, but its timing - two years after the Berlin wall began to be erected, and six months on from the Cuban missile crisis - drew attention to its commitment to the need for improved relations between states, not least in the form of east-west détente.

John XXIII had been elected to the papacy in 1958 after numerous ballots. The former Angelo Giuseppe Roncalli had been one of fourteen children from a poor family, and reached the top job at the age of 76 and to the surprise of most Catholics. He was expected to be a caretaker after the twenty-year papacy of the austere and rigid Pius XII. But his short rule brought more than mere stability: it led to remarkable changes and reforms, culminating in the Second Vatican Council which started in 1963.

The Catholic church had huge problems at the time, many of them stemming (as they do now) from issues around sexuality. Beyond these the 1960s were notable for the rise of a strand of progressive thinking in parallel with the liberation-theology movement across much of Latin America. In western countries, many young Catholics were becoming markedly politicised, and decades later substantial numbers of them retain the outlook they acquired then - even if they may have long since given up the practice of their faith.

It was said in the mid-1960s that if you subtracted the Jews, Quakers and Catholics from the ranks of the Campaign for Nuclear Disarmament, the movement would be set back many years. That strand of radical Catholicism has persisted, often in dedicated peace movements such as Pax Christi but also in more formally linked groups such as the many Justice and Peace Commissions.  

Fear and hope in America

For these groups, Francis’s words will be especially welcome. Many ex-Catholics too probably feel quite a warmth towards him. But Laudato Si will likely have a very particular impact on one political community at a very specific time: conservative American Catholics as the presidential-election campaign for 2016 approaches.

This is already shown by the reaction to the pre-publication leaks, as Republican presidential hopefuls took issue with Francis while treading the narrow line between criticising his words without alienating Catholic potential voters. Their problem stems from their own deep doubts over, if not outright denial of, climate change. But an added concern is that Laudato Si links environmental issues to the state of the world economy and today's wide socioeconomic divisions. In this respect the encyclical both strikes at the heart of the denialist community and implies deep suspicion of dominant neoliberal ideology itself.

Moreover, an added worry is the possible reaction of some American bishops. An early instance is the announced plan of the Archbishop of Miami, Thomas Wenski, to undertake a series of sermons and homilies on climate-change issues and the demands of the encyclical. This is significant in two quite different ways. One is that Florida is particularly susceptible to sea-level rise and extreme-weather events; the other is that two of its most senior politicians, Senator Marco Rubio and former governor Jeb Bush, are Republican contenders for the White House - and Catholics.

In terms of its worldwide influence and its support for a movement that is far more confident than ever before, this encyclical may already be regarded as the most notable event in the current papacy. But its most powerful significance may lie with the specific impact on just one part of the United States's political scene. Perhaps this was one of the main intentions all along.