During the daylight hours, plants produce oxygen. At night, they consume oxygen and release carbon dioxide. All things are in balance in this respect as while it is night in some places it is daylight in other locations at any given point in time.

In Al Gore's film, "An Inconvenient Truth", he shows a chart of rising carbon dioxide levels in the earth's atmosphere. All along the trend, it shows regular spikes and troughs, while retaining an overall rapidly rising trend in recent years.

The regular spikes and troughs are explained in this way:

Most of the land mass of the earth is in the northern hemisphere, and most of the vegetation is Northern hemisphere. During autumn and winter, the leaves fall and exhale carbon dioxide (through decomposition). Throughout the spring and summer days, leaves grow and inhale carbon dioxide. So, when it's winter in the northern hemisphere; global CO2 levels rise quite sharply and fall again during the warmer months.

So, should we all be planting evergreens or non-deciduous trees?

I've been trying to get a handle on this as I've been reading a lot that says deciduous trees are *better* than evergreens in relation to global warming. What I've researched so far states that deciduous trees have the advantage, not so much in relation to storing carbon, but because deciduous trees are usually broad leaved, they reflect the sun better. During winter, when the trees are bare, it allows the snow covered ground to have.

But will this "reflection" effect be enough to counteract rising carbon dioxide levels? Do deciduous trees, through their constant leaf regeneration, consume more carbon dioxide - taking it out of the air and converting it into solid carbon based substances - or does the winter "exhaling" effect and period of dormancy equal or override any gains?

I'm truly curious about the deciduous vs. non-deciduous question :).

By the way, Al Gore's "An inconvenient truth" is a very interesting movie (underlying politics aside). It's certainly well worth seeing.

Another interesting little side note: Increased carbon dioxide levels can affect photosynthesis; the process by which plants create food and oxygen. I've read that some plants, upon sensing an increase in carbon dioxide, slow down photosynthesis in a "negative feedback" response.

It's all fascinating and equally frightening stuff.