Are you dreaming of a White Christmas?  I know I am.  San Diego has beige Christmases at best.  If we want snow, we have to head for the mountains or manufacture the stuff. 

That said, a growing consensus of scientists is concerned that White Christmases may become a rarity for everyone, not just the privileged few living in Southern California.

It's a big world we live in.  It's so big that we still don't have a picture of the whole thing.  At some point, someone will send up a satellite that will snap a family photo of our planet, but for now, we barely can resolve the curvature of the globe with high-flying sounding rockets.  It is difficult to imagine something as tiny as a single species having a profound effect upon an entire planet.

And yet, that is exactly what may be happening.  Every year, humanity puts out six billion tons of carbon dioxide.  It's a relatively harmless gas as industrial byproducts go.  It certainly isn't Strontium 90 or even coal dust.  But its effects are far-reaching. Carbon dioxide is transparent to light but opaque to heat, which means it lets in the suns rays, but doesn't let heat from the Earth escape.  This is called the "Greenhouse Effect."  To some extent, we rely on this effect; without it, the Earth would be much chillier. 

However, the amount of carbon dioxide we are putting into the atmosphere is enough to measurably increase the Greenhouse Effect, thereby raising the global temperature.  It has been predicted (and most-recently related in Asimov's science fact article in the January 1959 Fantasy & Science Fiction) that in 350 years, the average global temperature will rise some 3.8 degrees Celsius, or a little more than half a degree per semi-century.

That doesn't sound like a lot, does it?  But it would be enough to melt the polar ice caps, flood our coastal towns, generate more inclement weather, and change the inhabitability of the Earth dramatically.  Good-bye, glaciers.  Hello, new deserts.

There even appears to be corroborating data: though the measurements were not as comprehensive in 1900 as they are today, it does appear that the global temperature has risen half a degree since then.  I suppose the real test will be to see if the global temperature continues to rise.  We shall have to wait and see if it is half a degree hotter in, say, 2013. 

It is likely, however, that there is no cause for alarm.  After all, long before then, we should have nuclear fission and fusion reactors powering the world, and fossil fuels will be a thing of the past. 

One dares hope.

Merry Christmas Eve. 

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