Thursday was the 40th anniversary of Earth Day, which was celebrated this year, according to the Earth Day Network, by more than a billion people in 190 countries.

When Earth Day started in 1970, few people would have expected it to become a globally observed religious holiday with its own ten commandments, including “use less water,” “save electricity,” “reduce, reuse, recycle,” and “spread the word.” The U.S. Environmental Protection Agency wants people everywhere to “commit to action” in defense of the Earth.

America’s leading environmental historian, William Cronon of the University of Wisconsin, calls environmentalism a new religion because it offers “a complex series of moral imperatives for ethical action, and judges human conduct accordingly.”

In other words, issues such as climate change are now much more than about “science.”

Environmentalists see humans engaged in acts of vast hubris, remaking the future ecosystems of the Earth. By playing “God” with the Earth, humans seek to become as God themselves.

The Bible’s book of Deuteronomy reveals dire consequences for those who try to “play God.” We learn that God will strike down sinners who “worship other gods,” causing them to suffer “infections, plague and war. He will blight your crops, covering them with mildew. All these devastations shall pursue you until you perish.”

It is no mere coincidence that contemporary environmentalism prophesies virtually the same set of calamities resulting from the warming of the earth—rising seas, famine, drought, pestilence, hurricanes and other natural disasters.

Even without realizing it, environmentalism is recasting ancient biblical messages to a new secular vocabulary. One radical environmental organization even declared that the most important commandment for human beings was to put “Earth First!”—renouncing the modern worship of science and economics that once provided a secular substitute for God.

Thus the Endangered Species Act is the new Noah’s Ark; genuinely wild places are the new cathedrals to find spiritual inspiration; Earth Day is the new Easter.

Much of the attraction of environmental religion is the disguised form in which it is presented. By appearing distinct from formal theologies and official churches of institutional Christianity, it can attract people who would normally not be involved, including residents of many nominally Christian nations and those who think of themselves as “spiritual,” while vigorously rejecting any suggestion that they should ever belong to “a religion.”

This comes as no surprise. A leading student of environmentalism, Thomas Dunlop, finds that “ever since Emerson, Americans who failed to find God in church took terms and perspectives from Christian theology into their search for ecstatic experiences in nature.”

“Environmentalism’s rhetorical strategies, points of view, and ways of thought remain embedded in this evangelical Protestant heritage,” he writes, even as this heritage has increasingly been disguised.

While the language is now different, environmentalists today, no less than the Calvinists of old, see “excessive” consumption—the constant demand for bigger and better, more and more—as a threat to the earth’s future.

But all this is much less novel than many people think. John Calvin wrote in the 16th century in The Institutes of the Christian Religion that God has “revealed himself and daily discloses himself in the whole workmanship of the universe.”

By visiting places where nature remains little affected by human actions, human beings will be “instructed by this bare and simple testimony which the creatures render splendidly to God.”

In the celebrations of Earth Day, however, there is admittedly one critical difference. The message is presented as an actual history of the world with concrete policy recommendations for today.

This places a greater burden on environmental theology than it is often able to handle. Success in stirring powerful religious feelings about the environment does not automatically lead to wise and effective policies.

The task for the future will be to draw on the core truths of the environmental message while adapting them to the full scientific and economic complexities of the 21st century.

When environmental religion seeks a return to an earlier primitive and natural existence, it is embracing Utopian dreams that easily can pose a danger to man and earth alike.