In March 2007, leaders of several conservative Christian groups sent a letter to the National Association of Evangelicals complaining that the organization’s focus on global warming is diverting attention from “the great moral issues of our time,” namely abortion and sexual morality. There is reason to suspect that the letter writers’ motivation was more political than moral, but the point needs to be made that climate change is a great – perhaps even the great – moral issue of our time.

In his Oscar-winning documentary and in many of his public appearances, Al Gore asserts that global warming is a moral issue, but he never explains what it is that makes it one. Instead, he lays out in graphic detail the horrific consequences of steadily increasing carbon dioxide levels in the earth’s atmosphere and appeals to our self-interest: “If we don’t start reducing carbon emissions now, really bad things are going to happen to us.” The understatement may be deliberate, but his title is “An Inconvenient Truth.”

Being the selfish creatures that we are, one might expect that an appeal to self-interest would carry the day. But clearly it isn’t working. We continue our profligate ways. Part of the problem is that people, even rational people, tend to discount negative consequences – or positive ones, for that matter – that lie in the future, especially if they appear to lie in the distant future. Some people believe that a technological fix will save us – ethanol, biodiesel, hydrogen-fueled cars. A smaller number is simply in denial.

This is one reason why the evangelical Christian movement’s recent attention to the issue of climate change is so welcome. Reducing carbon emissions is not just the smart thing to do; it’s the right thing to do. Ignoring or dismissing the problem is not only unwise; it is morally wrong. But why is it wrong?

The relationship between environmentalism and Christianity has been contentious. In a provocative and widely anthologized essay that first appeared in the journal Science 40 years ago [March 10, 1967], the medieval historian Lynn White, Jr. argued that our ecological crisis is rooted in the Judeo-Christian notion that God gave mankind dominion over nature – that man, formed in God’s image, is apart from nature and not a part of nature. According to this view, nature has no intrinsic value. It exists solely to satisfy the needs of mankind.

White’s essay prompted an impassioned response from Christian apologists. They cited chapter and verse to disprove his claim that man’s rapacity enjoys biblical sanction. White’s argument did not rely exclusively on scriptural interpretation, however, and the responses fell short of a refutation. Nevertheless, they did succeed in drawing attention to a biblical alternative to the notion of dominion – the concept of stewardship.

By characterizing man’s responsibility toward nature in terms of stewardship, the moral dimensions of our relationship to the natural world begin to emerge. But this biblical interpretation presupposes that nature is, in effect, God’s property, that we humans are God’s servants, and that we are obliged to care for our Master’s property. To the extent that Christians or other believers in a God of Creation find this argument compelling, we should be grateful. But a moral argument is needed that does not rely upon such religious beliefs.

What does it mean to be moral outside of a religious context? Behaving morally is a matter of paying due regard, in all our deliberate actions, to the interests and the well being of others. Morality requires that equal interests be treated equally regardless whose interests they are, especially basic interests that all humans have in common.

Some interests are more important than others but never because they are my interests, or yours; and not because they are the interests of present generations rather than those of future generations.

Clearly, our children have the same interest in a livable environment that we have, and so too their children, and their children’s children. This is the moral truth embedded in the bumper sticker slogan reminding us that “we don’t inherit the earth from our ancestors; we borrow it from our grandchildren.” The interests of our near and distant descendants in a livable environment have a moral claim on our behavior now.

Some environmental ethicists go farther and point out that humans are not the only beings that have an interest in a livable environment. All living things share this interest equally. And since morality requires that equal interests be treated equally, regardless whose interests they are, polar bears and pine trees also have moral claims on our behavior.

But we need not embrace this final implication to assert with confidence that global warming is the greatest moral issue of our time. What makes it the greatest moral issue of our time is the sheer magnitude of the looming catastrophe and the staggering number of people who will suffer as a result of our failure to do the right thing now.

If you want to know what Jesus would do, Jesus would drive a Prius.

–David Tebaldi, Executive Director, Massachusetts Foundation for the Humanities