Eighty-six prominent figures in the movement, among them leading pastors, the heads of evangelical colleges and the Salvation Army, released a statement yesterday warning that "millions of people could die this century" because of global warming - most of them in the earth's poorest regions.
Until recently global warming has not been a priority for evangelicals, most familiar for their uncompromising stances on social issues such as abortion and gay marriage, and their emphasis on the family. "Many of us required considerable convincing" that it was a problem, the statement acknowledges. But, it declared: "Now we have seen and heard enough."
The manifesto will be followed up with information campaigns at evangelical churches, schools and universities across the US, supported by radio and television broadcasts. All will spread the message that the government must act to curb carbon dioxide emissions, preferably by "cost-effective, market-based mechanisms".
That last is a nod in the direction of the business community, which evangelicals have generally supported in the past. But the new urgency - spurred by Hurricane Katrina and by the devastation of drought and starvation, witnessed first hand by evangelical missionaries in the Third World - is striking nonetheless.
The initiative is actively opposed by some of the biggest names in the movement - among them James Dobson, the head of the influential conservative group Focus on the Family, who signed a public letter last month claiming "global warming is not a consensus issue", and urging the National Association of Evangelicals, the movement's umbrella group, not to take a position on it.
Thus far the association has not done so - but there is little doubt which way it is moving. Although neither Ted Haggard, its president, nor the Rev Richard Cizik, the vice-president, has signed the manifesto, the latter made his feelings plain in a television interview last month. "We, as evangelical Christians, have a responsibility to God, who owns this property we call Earth," Mr Cizik told the PBS public broadcasting network. "We don't own it. We're simply to be stewards of it. And if climate change is occurring, can we simply ... pretend it isn't happening?"
Such sentiments are not those of the Bush White House, which has resolutely played down climate change and mankind's responsibility for it. Arguing that market forces will resolve the problem, it has regularly tried to gag anyone in the administration who suggests otherwise.
But unease among evangelicals will only have grown after last week's State of the Union address, in which Mr Bush - though he referred to America's "addiction to oil" - did not once mention climate change or global warming. And their unease will not be easy to ignore, given the political importance of the evangelical vote. In 2004 it split four to one in favour of Mr Bush, accounting for a third of his support.
Yesterday's statement is also proof of how religious groups feel increasingly obliged to speak out on global warming. The trend has seen the religious right make common cause with liberal Episcopalians and others on the "religious left", joined by some Orthodox, Catholic and Jewish groups. In 15 states, interdenominational groups are seeking regional standards to reduce emissions, Paul Gorman, director of the National Religious Partnership for the Environment, told The New York Times.