For starters, it looks like the planet has grown a tad toastier over the past century -- by about 0.6° C, or so. That's a bit iffy, since the Earth hasn't been cooperative about warming consistently. In fact, according to NASA, the United States have grown a bit cooler since about 1940. But it appears that the Earth (aside from the typically contrary U.S. of A.) has warmed a bit.

Is this unusual?

Errr ... That seems to be anybody's guess. Apparently, the ancient Sumerians never got around to launching weather satellites, so climate data is sparse until pretty recently. As the Reason Public Policy Institute pointed out in its Plain English guide to climate change:

[R]ecordings of the temperature only cover about 150 years, less than 0.000004 percent of the entire pattern of evolving climate. In fact, temperature records are spotty before the 1950s and only cover a tiny portion of the globe, mostly over land.

For all we know, Mother and Father Nature have been battling over the thermostat for the last million years.

But allowing that temperatures have gone up over the last century, the next question is: why?

Well, some folks say the planet needs a Mylanta. That's right: bad gas.

That's the theory, anyway. "Greenhouse" gases such as CO2 and methane have been increasing in concentration over the decades, and may well be capable of turning up the heat worldwide.

CO2 received much of the initial notice, but only about 5.5%, tops, of the gas comes from human sources -- nature cranks the stuff out by itself in copious quantities from the oceans, volcanoes and the exhalations of creatures feathered and furred. That sort of limits human options if CO2 is the problem.

Methane is a bigger worry. Not only is it a more powerful warming agent than CO2, the majority of methane output comes from human sources -- or human-controlled sources, when you take into account flatulent cows. As much as 16% of the stuff exudes from old Bossy, out in the field (and you wondered why everybody made her stay out in the field). Other big sources include rice cultivation and oil production.

Then there are those troublesome CFCs, like the freon you need for your air conditioner and now have to buy from a guy who smuggles it from Mexico. Once considered warming gases, CFCs were then reappraised as cooling gases, and now are considered to be doing something, though nobody's sure what. CFCs are entirely of human origin.

Adding a further complication is a likely source of warming that lies outside the reach of people, cows and even the Earth itself. As NASA researchers wrote in their assessment of the United States' climate, "changes of solar irradiance (the brightness of the sun) are difficult to dismiss as a mechanism of climate change, because there are observed correlations of solar variability and climate change."

So that upward-creeping thermometer could be a result of human-made gases in the atmosphere, natural gases, changes in the sun, or a combination.

But it's bad, from whatever source, right?

Ummm ... could be.

Many people are certainly worried. Even a London Daily Telegraph article eagerly foreseeing balmy days in Scotland conceded that, "the Mediterranean region would face increased desertification, water shortage and forest fires."

Other sources see coastal flooding from melting ice caps. They predict growing problems with pests, disease and violent weather from changes in the climate.

A worst-case scenario has the climate changing to such an extent that it passes a point of no return and renders the Earth essentially uninhabitable.

But not everybody agrees that even already-hot equatorial regions face catastrophe from a warming planet. A Heartland Institute report suggests that increased atmospheric CO2 is just what the botanist ordered when it comes to keeping crops happy and healthy.

In his book "Climate of Fear," the Cato Institute's Dr. Thomas Gale Moore argues that past periods warmer than today were times when humans and their civilizations flourished.

Shivering Russians, Scots and Scandinavians would probably agree.

So, is global warming man-made or natural? Is it good, bad or indifferent?

Well, speaking as a man who hasn't formally studied science since high school oceanography (the girls were cute and we smuggled beer on the field trips to the beach), I think it's safe to say that nobody really knows.

That said, I'm a bit leery of folks who claim that climate change, even if caused by human sources, is assuredly a good thing. I mean, when you were a kid playing with a chemistry set, it seemed like a good idea to pour the blue stuff into the smelly stuff -- right up until that loud BANG. Then your best friend's eyebrows went missing.

Unintended consequences can suck.

We know that the Earth is a pretty good place to hang out as things are now, and we don't know what the place will be like if we crank up the furnace. All other things being equal, it could be good idea to avoid doing things that might mess with global property values.

But all other things aren't equal. Nobody is pumping greenhouse gases into the atmosphere out of boredom. Agriculture and energy production play a large part in the emission of gases like CO2 and methane. If you want to completely cease the production of such gases, you have to shut off the lights, unplug grandma's respirator, and promise not to eat. Ever.

But maybe the production of potentially troublesome gases might be reduced, not eliminated.

In fact, that's what you would expect from increasing efficiencies in technology. It was once OK to pour smoke into the air in order to produce electricity, medicine or affordable clothing. There was no alternative and arguing about it was pointless. But that level of pollution shows a lot of waste from inefficient processes; technology has since improved to reduce such waste and the resulting pollution. Were your neighbor to set up an old-fashioned steam engine in the backyard now and begin bathing you and your house in coal soot, you'd be justifiably ticked-off and treat the matter as an assault on your person and property.

The same approach would seem to make sense in dealing with greenhouse gases. If it's a choice between producing penicillin and minimizing potential problems, someday, from too much CO2, we'll take the antibiotics, thank you. But technological advances should allow us, over time, to reduce pollutants that pose threats to people without taking drastic steps that also pose threats to people.

And that's exactly what's been happening -- but you wouldn't know it from the proposed "solutions" to global warming concerns. Explaining why the Kyoto Treaty is doomed, the Pacific Research Institute pointed out that the treaty placed the greatest burdens on countries like the United States, even though:

The U.S. uses the most advanced technology available to make us more energy efficient than any other nation. For example, India uses three times the energy and emits four times the carbon dioxide per unit of GDP than the U.S., and China use five times the energy and emits eight times the carbon dioxide....

Almost every breakthrough environmental technology has come out of the U.S. Most recently, scientists have announced the successful completion of a revolutionary fuel cell operating on gasoline that will double the fuel economy of today's automobiles and reduce automobile emissions of greenhouse gases by one-half, which currently account for one-third of all greenhouse gas emissions.

The Kyoto Treaty's restrictions, according to the Acton Institute, "would exact a $348 billion penalty on the American economy in 2010 alone." That would mean a hobbled economy and a likely slowdown in the sort of technological innovation most likely to reduce human contributions to climate change.

The world may well be warming and humans may play a role. That's a matter worth thinking about, since we hold the deed to the planet and the realtors haven't come through with an alternative.

But if global warming is a concern, it's because it poses a threat to the quality of human life. Any proposed solutions have to make things better, not worse.

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