It is human nature to jump to conclusions based on sparse evidence.

Our hunter-gatherer ancestors did not have time to analyze data before deciding whether an onrushing lion had honorable intentions.

Because of this unintentional bias, our sophisticated brains took upward of 35,000 years to understand that the heavens do not revolve around the earth, because we see them moving while the earth apparently stands still. Before we got it, we invented impressively convoluted schemes to explain the heavenly motions to avoid giving up what we “;knew”; to be true. The scientific revolution that began with Copernicus and culminated with Newton cleared up this crisis of confusion, but the paradigm change spanned 144 years.

Two and a half millennia ago, Aristotle's science was hindered by his belief that physical and chemical processes obeyed the laws of biology. Not much progress was made until we recognized that physics and chemistry are the fundamental sciences.

The life sciences and earth sciences share much in common, both operating on the fundamentals of physical and chemical laws. Earth is not alive in the biological sense, but it is physically alive, and its physical spheres intertwine with the biosphere in a unique and complex planetary homeostasis.

Earth science studies are similar in many ways to epidemiological observation. They differ markedly because we have only a few terrestrial planets to study, our planet is very large and its processes operate on a geological rather than a human time scale.

This puts us at a disadvantage when we are trying to ascertain the toxicity of “;supplements”; of carbon dioxide and other anthropogenic substances. Many forms of unintentional bias not unlike that which blocked our abandonment of geocentrism stymie us.

Correlation is a relationship between two or more objects of study. The correlation between people who smoke and people who drank milk is close to 100 percent. The causal conclusion that drinking milk leads to smoking is probably invalid.

It might seem that to determine whether carbon dioxide influences Earth's heat budget is merely a matter of taking Earth's temperature, measuring carbon dioxide concentration in the atmosphere, then looking for a correlation.

The correlation is there. Earth's temperature is increasing in concert with greenhouse gases. Can we be sure which is cause and which is effect?

Confounding the problem are multiple variables (carbon dioxide plays multiple roles in geochemistry) and nonlinearity of the relationship (at higher temperatures the oceans release stored greenhouse gases resulting in positive feedback). Because of these and other confounding factors and bias, we cannot easily determine causality and thus cannot predict with certainty what the effects of mitigation might be.

All of this and more is wrapped up into this complex political, social, scientific quandary we call global climate change.