Despite the fact that we can't see oxygen or carbon dioxide in our air, the existence of these invisible gases is not a radical theory but a well-established science. Back in the 1800s, physicist Michael Faraday used a series of experiments involving a candle flame to show children how to reveal such otherwise invisible gases. He also demonstrated how different invisible gases behave quite differently from one another. Some fed flames, for example. Some extinguished them.

I thought about Faraday's lectures when I read this story over the weekend in the New York Times, describing a controversy that surrounds a Discovery Channel documentary about the Earth's polar regions.

According to the story, the film is full of visual evidence for melting glaciers, shrinking sea ice and threats to wildlife. And yet, there's a conspicuous absence of any mention of carbon dioxide or other greenhouse gases as probable causes:

The vast majority of scientists agree that human activities are influencing changes to the climate — especially at the poles — and believe that the situation requires serious attention. That scientific consensus is absent from "Frozen Planet," for reasons that shed light on the dilemma of commercial television, where the pursuit of ratings can sometimes clash with the quest for environmental and scientific education, particularly in issues, like global warming, that involve vociferous debate.

Including the scientific theories "would have undermined the strength of an objective documentary, and would then have become utilized by people with political agendas," Vanessa Berlowitz, the series producer, said in an interview.

She added, "I feel that we're trying to educate mass audiences and get children involved, and we didn't want people saying 'Don't watch this show because it has a slant on climate change.' "

All this emphasis on consensus obscures the fact that there's some very basic physics and chemistry that could help people understand why scientists are worried about carbon dioxide.

Is the physics of gases now an ideology? Is it a now a political statement to explain the way carbon dioxide interacts with thermal infrared radiation? I can see why the makers of this documentary don't want to get too preachy. I can see why they don't want to bore children with a big nerdy science lecture either. But among other things, Michael Faraday showed it's possible to make science engaging to kids and adults.

It's a shame that a documentary like this can't offer just a little bit of science explaining what carbon dioxide is, how it traps heat, and why our planet would be a big snowball without our warming blanket of greenhouse gases.