Carbon-offsetting is a dirty business. And I'm not talking about getting your hands soiled from planting trees. I refer to the vehemence that surrounds debate as to its merit.

Nothing - not the war in Iraq, the death penalty, or stem-cell research - has recently brought out the passion I have seen when the conversation turns to global warming. And I must be a knucklehead. Because I seem to be the only person who doesn't have the entire subject figured out, despite lots of effort.

My starting point was Al Gore's movie

An Inconvenient Truth

, which I found compelling even when I didn't understand it. I also read the companion book. It, too, made a strong case that the burning of fossil fuels is heating Earth to a level that, unabated, will soon wreak havoc.

But then I watched Glenn Beck's hour-long CNN special on the subject,

Exposed: The Climate of Fear

, in which he gave a platform to scientists who don't often get heard on the issue. Maybe it's all bunk, I thought.

My own interview with Penn professor Bob Giegengack introduced a new subtlety to that side of the debate. Professor "Gieg" told me, "What I am unhappy with in the Gore film is the extent to which the consequences of the processes currently under way were exaggerated with the intention of appealing to public fear."

A friend then introduced me to Bill Chameides, a Yale-educated Ph.D. who at the time was the chief scientist of the Environmental Defense Fund; he has since been named dean of the Nicholas School of the Environment and Earth Sciences at Duke University. Chameides made the scientific case for global warming. Again, my head spun.

Which is about the time I read Inquirer writer Sandy Bauers' story about carbon offsets, which featured a woman willing to write a check to reduce her carbon footprint. I called one of the carbon-offset entities identified in the story, Carbonfund.org, to interview its spokesman, Russell Simon. I could tell he was leery of speaking with a reputed "conservative" talk-radio host, another sign of just how stilted this debate has become.

I told him I drive a Ford F-150 pickup truck (which probably confirmed his stereotype). He wanted to know the year, engine size, and how many miles I drive. Then he did a calculation and told me my truck probably cranks out about 4.36 tons of CO2 emissions per year. When I told him I wasn't giving up the truck, he suggested I support a reforestation program by writing a check for $24 to offset my CO2 output. He promised to use the money to plant a tree in Nicaragua.

I agreed and made it clear that while I'm still unsure about global warming, I'm all for more trees. If he plants one, terrific. And if not, I'm out the cost of a case of beer.

All of this played itself out on my radio show. The audience reaction? You'd have thought I sent the check straight to Osama bin Laden.

Typical is this e-mail: "My wife and I have been listening to your show daily for several years now. Keep up the great work. HOWEVER, your failure to take a clear position on global warming is very frustrating and disturbing. Global warming is a political issue, not a scientific issue. You're either FOR affirmative action or you're AGAINST it. You're either FOR legalized abortions or you're AGAINST them. You either believe in God or you don't. Please do a little homework and pick a side!"

So hatriolic is this debate that I'm inclined to pick sides based solely on who I believe is less closed-minded.

The main claim in the global-warming argument is well-known: Man's burning of fossil fuels is warming our planet to a level that will have catastrophic results unless remedied. The skeptics have peppered me with a handful of repeated arguments as to why this is not the case. So I went back to Chameides at Duke and asked him to respond to five of the most common. Here they are, along with a short version of his response.

1. Scientists like those on the Intergovernmental Panel on Climate Change (2,500 scientists who signed a statement that fossil-fuel emissions are responsible for a steady rise in atmospheric temperature) are just exaggerating to get more funding.

Chameides: That implies a conspiracy that is unbelievably wide-ranging. It's more an attack on the people researching climate change than a challenge to their conclusions. It also contradicts the attitude science has been built on for centuries: The goal is to challenge accepted wisdom, not simply prop it up.

2. Water vapor is a more dangerous greenhouse gas than CO2.

Chameides: Such a claim is analogous to lighting a match, starting a forest fire, then blaming the trees for the fire. Consider this persuasive difference between the origin and roles of water vapor and CO2 in the atmosphere. The amount of water vapor in the atmosphere is determined by temperature - not by any direct human action. On the other hand, we do have control over the amount of excess carbon dioxide in the atmosphere.

3. Human carbon dioxide emissions are tiny compared with those of natural sources.

Chameides: True, but even the "slightest" additional amount of CO2 throws off the balance between natural emissions and natural absorptions. Besides, by examining the atomic structure of the additional CO2 now being seen in the atmosphere, we can prove it comes from fossil fuels - that is, from us.

4. The observed warming is all due to solar-radiation variability, not human activity.

Chameides: Monitoring of the sun's energy output over the last 20 years shows a change of less than .01 percent. In other words, the amount of heat beaming from the sun hasn't changed sufficiently to account for the degree of warming being observed.

5. Mars and Pluto are warming, too, and they have no smokestack industry as far as we know.

Chameides: True, but these planets are warming for reasons that don't apply to what's happening on Earth. Mars has warmed due to changes in snow and sand caused by weather variations. Pluto's warming is related to its position relative to the sun.

Where does all this leave me? I believe human conduct is warming the Earth. But not to the extent caused by the global-warming debate.

Michael Smerconish's column appears on Thursdays in The Daily News and on Sundays in Currents. Michael can be heard from 5:30 to 9 a.m. weekdays on "The Big Talker," WPHT-AM (1210). Contact him via http://www.mastalk.com.