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The climate change argument has five parts:

(1) Global warming is underway.

(2) Global warming currently underway is different from periods of global warming in the past. This time it is hockey-stick global warming. Hockey-stick global warming means that temperatures will go up and up and up and up and up and up and up and up, indefinitely. Without intervention, temperatures will never decrease again.

(3) The consequences of hockey-stick global warming will be catastrophic.

(4) People’s activities account for hockey-stick global warming.

(5) Government intervention and social action can stop hockey-stick global warming.

Here’s the problem: if you express skepticism about any one of these steps, advocates of (5) accuse you of being a climage change denier. That means you deny the truth of step (1). Anyone who would deny the truth of step (1) is not worth talking to, because people who deny scientific evidence are whacko. If you think I have overstated the reason public discussions about climate change seem unproductive, you have not attended to the so-called discussion.

In fact, people who doubt (2), (3), (4), or (5), do not necessarily deny (1). Convincing evidence indeed indicates global climate change is underway. For those who like visual evidence rather than computer simulations, satellite photographs of ice on the Arctic Ocean do well. To say that global climate change is underway is not controversial because, from what we can tell, global climate change has occurred since the earth formed. To say that global climate change is not underway would actually be a silly thing to say. That would be controversial.

Happily, public discussion of climate change does not center on statement (1). Discussion of the subject since the 1980s or so concerns the nature of climate change in this era, its consequences, its causes, and how we should respond. What, if anything, should we do about it?

Notice that item (2) in the list above is the longest. Acceptance of the hockey-stick model underpins acceptance of the belief system that encompasses statements (3), (4), and (5). If you do not accept (2), you need not trouble yourself with (3), (4), and (5). Secular climate change – including changes in global temperatures that have proceeded since the earth formed – has nothing to say about the last three statements.

Hockey-stick climate change may sound a little discredited, perhaps like the flat-earth society, but the term is useful to describe the shape of the graph that launched the movement to cut CO2 emissions and prevent catastrophe.

One observer calls this plot the most controversial graph in science.

What are three characteristics of the hockey stick model for global climate change?

(1) Global temperature averages bounced along in a predictable band for millennia. The planet’s natural thermostat worked.

(2) Starting around 1900, global temperature averages started to increase at a rapid rate.

(3) Over a century after temperature stability ended, the rapid increase in global temperature continues.

Here are some concluding thoughts. As noted, the statement that global climate change occurs now is not controversial. We know periods of warming and periods of cooling alternate over time. To add that images and other observations of melting ice packs indicate an upward trend in global temperatures is not particularly controversial, either. Defense of the hockey-stick model, however, requires more inference than most people are willing to swallow. Put simply, the hockey-stick model does not follow directly from current data on global climate change.

People who advocate that we do something about global warming depend upon the accuracy of the hockey-stick model, whatever they might prefer to call it, and whatever reasoning they might use to substantiate it. When someone questions the accuracy of the model, or of the reasoning that supports it, advocates jump to their accusation of denial, self-consciously grouping their opponents with Holocaust deniers. They can do better than respond with the mistaken idea that people who disagree with them are whackos. To convince people who think about these issues even a little bit, they need a better argument than, “Anyone who believes global warming is a myth is too nuts for me to bother with.”

People who are skeptical about global warming are skeptical about statements (2) through (5). Generally they do not question or criticize statement (1). Advocates who dismiss skeptics as climate change deniers serve their own cause poorly. In fact, they make their cause look like a militant propaganda machine that does not countenance contradiction.