When Pope Francis addresses the Joint Houses of Congress in Washington about a fortnight hence, Catholic politicians, who make up nearly a third of Congress, could be faced with an interesting clash of loyalties.
For if, as is to be hoped, Pope Francis uses the opportunity to build on his June encyclical calling for an urgent response to climate change, Catholic Republicans in particular might wish he had stayed away.
One of them, House Speaker John Boehner, said members looked forward to receiving his message.
The message in the 191-page encyclical, Laudato Si' (Praise Be to You) is crystal-clear: ''Humanity is called to recognise the need for changes of lifestyle, production and consumption, in order to combat this warming or at least the human causes which produce or aggravate it.''
Pope Francis is scathing about the ravages wrought by exploitative capitalism and consumerism on the planet and the poor.
This is a moral issue as well as an environmental one, he says, for the future of humankind is at stake.
That is hardly new.
Scientists observe sourly that they've been drawing attention to the crisis for years, yet only when the Pope recycles their conclusions do some people sit up and listen.
Not everyone, however.
Catholic Republican presidential candidate Jeb Bush told the Pope, in effect, to butt out.
''I don't get economic policy from my bishops or my cardinal or my pope,'' he said.
''I think religion ought to be about making us better as people and less about things in the political realm.''
So did the Senate's most vociferous climate-change denier, James Inhofe, a Presbyterian, who insists that fossil fuels are necessary for a strong economy, which in turn helps lift people out of poverty.
So we need to destroy the global village to save ourselves?
No, says Pope Francis, we save ourselves only by saving the planet on which all life depends.
Indeed, the strength of Laudato Si' lies in its highlighting of the moral issue.
Humanity is an integral part of the environment, and respect for one must be complemented by respect for the other.
The politics of selfishness and greed, which are having a dream run, are destructive of both.
A central theme of the encyclical is that Earth is to be shared as a collective good, without the wealthy assuming they have greater rights over its bounty than those considered ''the disposable of society''.
Political and economic decisions need to take into account a better distribution of wealth, concern for the environment and the rights of future generations.
Pope Francis pays tribute to the massive contribution of technology in improving people's quality of life, but laments that this has not been matched by a parallel development in human responsibility, values and conscience.
An authentic ''human ecology'' would recognise how interconnected everything is.
A consumerist vision of human beings undermines cultural identity, community values, social opportunity, a sense of belonging, and human dignity.
It is disdainful of the common good, which ''society as a whole, and the state in particular, are obliged to defend and promote''.
So what's to be done?
Live more simply, says Pope Francis.
Reject ''a magical conception of the market''.
Promote ''a profound humanism'' as the basis of society.
See humanity as one people living in a common home.
Think long term.
Encourage an all-inclusive culture of care.
Look for a consensus on a sustainable environment beyond national interests, and find the political will - and build the international institutions - to act upon it.
Is this really what religion is about?
Too right! Care for the environment raises issues of what it means to live responsibly as humans today.
Where does true wholeness lie - for individuals, societies, nations?
Pope Francis is calling for repentance in the biblical sense of a change of mind and direction, a turning away from damaging and self-destructive living to life in harmony with the planet and each other.
Pathetic responses such as New Zealand will take to the United Nations Climate Change Conference in Paris in December play to the gallery of self-interest, but short-change future generations.
The encyclical has one big blind spot: Pope Francis plays down overpopulation, a key and continuing element in the crisis.
He also sets his plea for the planet within a rigidly theistic framework that many he would like to influence find obsolete.
A wider perspective would have given his message more immediacy and grunt.
Still, Pope Francis' call for a broader vision shines through: ''There can be no renewal of our relationship with nature without a renewal of humanity itself.''
• Ian Harris is a journalist and commentator.
