Last Sunday (Earth Day, no less), the Discovery Channel aired the final episode of its Frozen Planet series. Titled "On Thin Ice," the episode captures the staggering changes in our polar regions being wrought by global warming -- shrinking glaciers, rising seas, and disappearing habitats. But there was one thing missing: in 45 minutes, not a word was uttered about why all that Arctic ice is melting. In an impressive feat of journalistic malpractice, Discovery completely avoided the fact that the burning of fossil fuels causes climate change, and thanks to a New York Times article, now we know why. Discovery has admitted to censoring itself because it wanted to avoid criticism from climate change deniers. This was a shameful decision, which is why thousands of people have joined Forecast the Facts in demanding an immediate apology and an explicit commitment from Discovery to make sure it never happens again.

For those keeping score at home, this is the second instance of self-censorship for Discovery's climate change compendium. Discovery was not even planning to run the "On Thin Ice" episode in the United States at all (it was broadcast in Europe), but the channel reversed course after activists cried foul. This looked like a victory for accurate reporting of climate change, until it became clear that the episode doesn't, you know, explain why the climate is changing.

So what's the big deal? In some ways, the content of "On Thin Ice" requires no additional context: the glaciers are receding, the animals are suffering, and the lives of people in the polar regions are dramatically changing. Surely any sensible person would look at these images and realize -- this is global warming, pure and simple. But of course we know that the climate conversation in the United States is anything but sensible, and in that light the omissions are glaring. An uninformed viewer would have walked away from the program without even a hint as to what was actually going on.

But the issue here goes way beyond the content that was omitted. The bigger problem by far is the rationale that Discovery offered. According to series producer Vanessa Berlowitz, talking about climate change "would have undermined the strength of an objective documentary." She added that, "we didn't want people saying 'Don't watch this show because it has a slant on climate change.'" Yes, you read that correctly. She said that mentioning climate science would make the piece less objective, and that she was worried that Discovery would be accused of having a "slant" on something that every major scientific association in the entire world has already agreed on.

Putting aside what a sad statement this is for Discovery's journalistic standards, what's really dangerous is the message its decision sends to media outlets everywhere, which translates as: "it's better to censor yourself than risk upsetting conspiracy theorists and propagandists who deny climate science."

Of course, for climate change deniers, this is what victory looks like. As Yale Project on Climate Change Communication director Anthony Leiserowitz explained to the NYT, Discovery is saying that they are "more afraid of being criticized by climate change 'dismissives' than they are willing to provide information about climate change to the large majority of Americans who want to know more about it." Conservative blog RedState put a more gleeful spin on the same conclusion, writing, "Happy Earth Day 2012, everyone! One day we may look back on this as the time when the tide began to recede -- that being the tide of Anthropogenic Global Warming hysteria..." It's a good bet that if you make the folks at RedState chortle with glee, you have done something terribly wrong.

The Discovery Channel's parent company -- Discovery Communications -- lauds itself as the "world's No. 1 nonfiction media company," and regularly trumpets its commitment to "educating" viewers. Running a documentary about climate change impacts and avoiding any discussion of fossil fuels and greenhouse gasses falls far short of their stated ideals. Which is why, if Discovery wants to maintain its credibility, it needs to immediately recognize its mistake and take steps to make sure it never happens again.

Perhaps the saddest thing in this whole affair is the high-minded rhetoric of the Frozen Planet producers, who said they "felt a sort of moral imperative to go and document the polar regions before they change forever." I have no doubt that their impetus was heartfelt. And I believe they convinced themselves that avoiding any mention of global warming's causes would make a bigger difference in the world, allowing them to "educate mass audiences and get children involved." Unfortunately, they were earth-shatteringly wrong in that calculation. As long as climate change is treated as an unutterable "scientific controversy," our society will be incapable of facing up to the problem and figuring out how to solve it. So the main effect of their self-censorship is to reaffirm the idea that the science of climate change is somehow in doubt.

I also believe, though, that the Discovery Channel will listen to the concerns of thousands of viewers, recognize its error in judgment, and take steps to avoid such missteps in the future. If nothing else, doing so would give the channel a much greater chance of seeing ice in the Arctic whenever they return.