|Ptolemaic system: forcing the data to fit the theory (emaze.com)|
As observations became more accurate in the 15th century, tweaks were added to the Ptolemaic system to fit the data to the model, which finally collapsed under its own complexity and the rise of the superior predictive heliocentric model.
While the historical parallel isn't exact, climate-change models are in the same state as Ptolemy's was, that is, they are unable to explain or predict Earth's temperature with any reliability. Only through tweaking and adjustments are the models able to explain what happened in the past.
Two factors, the sun (obvious) and cloud cover (not so obvious) appear to have a far more important effect on global temperatures than carbon dioxide. Arguing that man-made CO2 is the primary factor in global warming could be as mistaken as claiming that the Earth is the center of the universe.
Even if global temperatures are rising, it's far from clear that the world overall would be worse off; for example, a little warming might be appreciated in Northern Canada and Siberia.
Also, if global cooling instead of global warming has greater than a remote possibility, it's more practical to spend $billions on increasing society's adaptability to change in either direction, rather than place all bets on curtailing carbon dioxide.
But then again I'm no scientist.