Few things get my goat more than global warming deniers. Here’s the basic science, which I learned in college from Nobel laureates — but this is paraphrased from none other than Shell Oil Company’s website:
1. Carbon dioxide’s chemical bonds trap heat (infrared radiation); this is called the greenhouse effect, and was proven in the 19th century.
2. Burning fossil fuels and trees increases the amount of CO2 in the atmosphere. Over the past 200 years or so, human activities have released ~350 gigatons (almost 800 quadrillion pounds) of carbon into the atmosphere. It is utterly, completely impossible to dispute this.
3. As a result, the atmospheric concentration of CO2 has increased by 40% in 150 years, or in 0.000003% of earth’s history — if the earth was one year old, this would’ve happened in ~1 second. This concentration appears to be higher than it’s been in millions of years, and certainly since humans have been around. Projections based on current trends indicate that CO2 could go to ~300% above pre-industrial levels during this century, reaching levels considered toxic to human health. I’ve never seen a serious attempt to debunk these facts.
4. Numerous studies and models of climate systems, both micro and macro, of earth’s history and future and those of other planets, show that climate systems are sensitive to changes in carbon dioxide concentrations. That is, this stuff matters.
5. The earth’s climate is warmer today than it’s been in a very long while. Land, sea, and satellite records all independently verify this, despite recent attempts to spread FUD about individual data points.
6. Therefore, humans burning fossil fuels have enhanced the greenhouse effect and are warming the atmosphere. I find it very difficult to logically dispute this if one accepts the points above — which, as I’ve noted, are all well nigh impossible to dispute.

Many of the professional deniers have accepted #5 above, and now say, “so what?” Well, I don’t think it’s prudent to run an uncontrolled experiment on the only planet fit for human habitation. Systems often prove much more fragile than we might expect: a 40% increase in CO2 concentrations might not sound drastic, but consider that a mere 11% increase in the concentration of iron in your body can kill you. Given that the cost of heading off a climate catastrophe is (a) not that expensive, at perhaps a few percent of GGP, and (b) can move forward any number of wonderful side agendas, why should we not pursue these policies?