Americans are considerably less favourably inclined to Pope Francis than they were a year ago, a new Gallup poll has found, two months before he is to visit the United States.

Pope Francis' favorability rating among the general public in the United States has returned to where it was when he was elected to the papacy and some believe his strong comments and capitalism and climate may be fueling that change .

Francis current popularity rating among Americans is now at 59 per cent, down from 76 per cent in early 2014.

The pontiff's rating is similar to the 58 per cent he received from Americans in April 2013, soon after he was elected.

Pope Francis' favourability rating among American Catholics has also dropped almost one-fifth in a little over a year.

In 2014, 89 per cent of U.S. Catholics said they viewed him favorably.

According to the poll published July 22, that figure stands at 71 per cent – a drop of nearly 20 per cent, or one-fifth, of the country's Catholics.

Similarly the percentage of other Christians who rate Francis favourably has dropped from 73 per cent to 52 per cent.

"With the official release of Pope Francis's encyclical on the environment [Lauadato si'], it's clear that several strains of thought prominent in the U.S. will be particularly challenged by the document," Chris Mooney commented in The Washington Post on June 18.

"That includes U.S. individualists who tend to support limited government and fewer environmental restrictions – [conservative radio host] Rush Limbaugh has already accused Francis of Marxism - and also those who perceive a strong conflict between science and religion."

Mooney wrote, "So in sum, here we have a leader of one of the world's dominant churches articulating - and soon, coming to the U.S. to further articulate - a vision in which science and faith are partners in a communal quest to protect the vulnerable from the rampant profit motive and exploitation of the Earth.

"For U.S. individualists and science-religion battlers, that is going to be serious cause for contemplation - which, perhaps most of all, is what Francis's encyclical is asking us for."

One commentator told Catholic News Agency that most Americans have a favorable view of Francis, but an apparent decline in their numbers may be due to his implicit challenge to American culture.

"Americans never react well when an international leader criticizes their culture," Dr. Kathleen Cummings, a University of Notre Dame professor of American Studies, told CNA July 24.

"Given that Pope Francis has done so implicitly in his recent remarks and writings, it is not surprising to see that his approval ratings have declined in the United States."

The Tablet, a UK-based Catholic newsspaper commented July 23, "The negative response to Laudato si' is often linked to the other anti-Francis tack taken by right-wing American Catholics – that his fierce critique of the free-market economic system only applies to Latin America, or indeed just Argentina, and hence says nothing about what happens elsewhere including the United States.

"This is to treat Pope Francis as a fool. They forget that he is not the first Pope to sound left-wing to their ears. Even the one that conservative Catholics in America tend most to admire, St John Paul II, had his encyclical Sollicitudo Rei Socialis rubbished in The Wall Street Journal as "warmed-over Marxism."