One of the more popular refrains from the climate change denial crowd is that we shouldn't be concerned about increased carbon dioxide levels because it's an essential ingredient for life. After all, plants absorb the gas as part of photosynthesis, so therefore it can't be bad and all the scientists and experts and Al Gore are wrong.

Last night Glenn Beck got in on the act, proclaiming that he learned in third grade that “plants need this dangerous invisible gas” and even showed us some time-lapse video a plant that was growing phenomenally well after receiving 180 times the amount of carbon dioxide typically found in the atmosphere.

This is facile beyond reckoning. I suspect that Beck is too ignorant to follow even the most dumbed-down explanation of why this is wrong, but I'll try anyway, using a metaphor that even he will understand -- Twinkies.

Let's say Glenn Beck is sitting on a trampoline eating Twinkies one at a time at a very steady rate. Everything is nice and stable, and there's nary a wobble to be observed. Every now and again a big box of Twinkies falls onto the trampoline with him, causing it to sag a little bit. But Beck loves Twinkies and quickly eats the entire box. After a while, the trampoline ceases to sag, and the whole system reverts to normal. Soon, bigger and bigger boxes of Twinkies start falling more often, causing the trampoline to sag more and more. But Beck, who just can't get enough Twinkies, is loving this. He's putting down box after box, not even stopping to call anyone a socialist. The boxes of Twinkies, however, are falling way more quickly than even Glenn Beck can eat them, and they start to pile up on the trampoline.

So now Beck is eating Twinkies three, four at a time, barely even taking the time to chew, and loving every second of it. There are yellow crumbs and creme filling everywhere. But the Twinkie boxes are falling faster and faster, putting more and more stress on the springs of the trampoline until finally they can't take anymore and snap. Beck comes crashing down, Twinkies and all, lying buried under a gigantic pile of snack cakes. The system has failed.

Obviously the analogy isn't perfect, but this is essentially what is happening to the planet's natural system for absorbing carbon dioxide and regulating the climate. It has no trouble dealing with the naturally occurring levels of carbon dioxide and can even handle the occasional spikes that occur when, for example, a volcano erupts. Plant life is a key part of the system -- 45 percent of all terrestrial carbon is stored in tropical forests. But as flexible as the system is, it has its limits, and when you start introducing higher and higher levels of anthropogenic carbon dioxide, it becomes overburdened and ceases to function. And when the earth can no longer regulate its own climate, all those plants that were happily absorbing that extra carbon dioxide are going to find themselves in dire straits, along with the rest of us.

So yes, higher carbon dioxide levels are beneficiary to plant life, just as higher Twinkie levels would make for a happier Glenn Beck. But to suggest that carbon dioxide's role begins and ends with plant growth is quite literally missing the forest for the trees.