1) Using their own reasoning rather than spitting out what they have seen on the internet.
2) Educated to make assumptions that involve PHD level interpretations of chemistry, biology, and environmental engineering.
3) Able to back up most of what they say.
I know there are a fair few, however, that make good arguments on both sides of the campaign against global warming. I for one do not believe it has a very substantial effect on the world (especially since people have predicted the warming of the planet since before the Industrial Revolution). As someone majoring in Environmental and Civil Engineering, I do think it's important to learn about. I do go to the Air Force Academy, so some might say I lean a little to the right, but I have always taken into account both sides before jumping to conclusions.
Here is a pretty interesting article I found with a credible source. Whether or not you agree is up to you, but I think its good to read:
The atmosphere is primarily composed of nitrogen (78 percent), oxygen (21 percent), argon (0.93 percent), and CO2 (0.04 percent). Many other gases are present in trace amounts. The lower atmosphere also contains varying amounts of water vapor, up to four percent by volume.
Nitrogen and oxygen are not greenhouse gases and have no warming influence. The greenhouse gases included in the Kyoto Protocol are each rated for warming potency. CO2, the warming gas that has activated Al Gore, has low warming potency, but its relatively high concentration makes it responsible for 72 percent of Kyoto warming. Methane (CH4, a.k.a. natural gas) is 21 times more potent than CO2, but because of its low concentration, it contributes only seven percent of that warming. Nitrous oxide (N2O), mostly of nature’s creation, is 310 times more potent than CO2. Again, low concentration keeps its warming effect down to 19 percent.
Now for an inconvenient truth about CO2 sources — nature generates about 30 times as much of it as does man. Yet the warming worriers are unconcerned about nature’s outpouring. They — and Al Gore — are alarmed only about anthropogenic CO2, that 3.2 percent caused by humans.
They like to point fingers at the U.S., which generated about 23 percent of the world’s anthropogenic CO2 in 2003, the latest figures from the Energy Information Administration. But this finger-pointing ignores yet another inconvenient truth about CO2. In fact, it’s a minor contributor to the greenhouse effect when water vapor is taken into consideration. All the greenhouse gases together, including CO2 and methane, produce less than two percent of the greenhouse effect, according to Richard S. Lindzen of the Massachusetts Institute of Technology. Lindzen, by the way, is described by one source as “the most renowned climatologist in all the world.”
When water vapor is put in that perspective, then anthropogenic CO2 produces less than 0.1 of one percent of the greenhouse effect.
If everyone knows that water vapor is the dominant greenhouse gas, why do Al Gore and so many others focus on CO2? Call it the politics of the possible. Water vapor is almost entirely natural. It’s beyond the reach of man’s screwdriver. But when the delegates of 189 countries met at Kyoto in December 1997 to discuss global climate change, they could hardly vote to do nothing. So instead, they agreed that the developed countries of the world would reduce emissions of six man-made greenhouse gases. At the top of the list is CO2, a trivial influence on global warming compared with water vapor, but unquestionably man’s largest contribution.
In deciding that it couldn’t reduce water vapor, Kyoto really decided that it couldn’t reduce global warning. But that’s an inconvenient truth that wouldn’t make much of a movie.