Why do I think humans are involved? CO2 levels are climbing exponentially. We're the only known source of extra CO2. The climate is measurably warmer. Coincidence?
The clincher is WHERE climate is warming. If atmospheric carbon is the cause, then temperature rise should be greatest in places where CO2 absorbs the most solar energy, reradiating it as heat. Moisture interferes with the absorption process, so if carbon is involved, heating should be greatest in the dryest areas. What areas have warmed the most? The edges of deserts and the Continental Arctic in winter (when water is frozen out of the atmosphere). That's why Fort Smith showed the warming: it's on the edge of the Great Plains, a dry area.
Conversely, Wilmington, NC and Meridian, MS were also tested and showed no warming. Why? They're in wet areas, near large bodies of water, which, if global warming theory is right, will be the last places to show warming.
Human involvement in global warming is also supported by large amounts of scientific evidence. If you want to argue about something, argue about the EXTENT of man-caused warming. That's still up in the air.
We are reaching the point in climate technology that within the next decade we should be able to forecast the exact amount of warming that will occur in any given locality. Then you will have something you can test in the field.