Isn't it great when people get together to reasonably discuss ideas? Sadly, this recent Australian Broadcasting Corporation1 clip isn't that. It features highlights of a climate change conversation between physicist Brian Cox and Australian politician Malcolm Roberts. Cox uses evidence to support the idea of global climate change, while Roberts denies the changes. Why is this still up for discussion? I won't rehash the details of climate change—others do a better job of it. But I think some of the points that Roberts raises are important to discuss in regard to the nature of science.

Roberts contends that science shouldn't be based on consensus but rather empirical evidence. Let's look at these terms as they relate to science.

What is empirical evidence?

Here is the Wikipedia definition:

Empirical evidence: also known as sense experience, is the knowledge or source of knowledge acquired by means of the senses, particularly by observation and experimentation.

I'll add my own definition. Empirical evidence is data collected in an experiment. Honestly, I never emphasize the empirical part—I just call it data. Sometimes people add "empirical" to mean that it is absolutely true. Unfortunately, no such truth exists in science. Science is sort of like Plato's allegory of the cave. In it, Plato says we are like people in a cave with our backs to a wall. Objects paraded in front of a fire cast shadows on a wall. We see only shadows and must determine what the objects are. This is how scientists do things. Here's a good example: No one has ever seen an electron. You can't see them with the naked eye; they're too small. However, there is great experimental evidence that electrons do exist, and scientists are pretty confident about some of their properties. But I wouldn't call it the truth.

Climate science also is difficult to measure. How do you know the temperature of the Earth? You can't measure it directly. You can't take a giant thermometer and stick it up the Earth's butt to find out if it has gotten warmer. Instead you must use many indirect measurements obtained via many different methods to estimate the temperature. It's not perfect, but it's the best available. With this, science always includes uncertainty in its measurements. But scientists are confident that the global temperature is rising, just as they are fairly sure about the mass of an electron.

This is the graph of global temperature that Cox used to support climate change. Let's be clear—this graph shows the data for global temperatures. Roberts said he wants the empirical data (I'm not sure what he really wants) and suggested that perhaps this data has been manipulated by NASA. I think Roberts is waiting for the temperature-up-the-butt graph. He won't get it.

What is scientific consensus?

Let me go with Wikipedia's definition of scientific consensus.

Scientific consensus: is the collective judgment, position, and opinion of the community of scientists in a particular field of study. Consensus implies general agreement, though not necessarily unanimity.

If science was one person, the consensus would be what that person said. But science is not one person. You will always find people with advanced scientific degrees who don't agree with the rest of the community. No one seeks unanimity, and not reaching the same conclusion is OK. But there is still a consensus. Together, scientists decide to use a particular model for some aspect of science, based upon the data available at that moment.

Here's an example: gravity. Everyone has a feeling for gravity. Is there a consensus model for gravity? Yes. Einstein's model of General Relativity has plenty of experimental evidence supporting it. Are there scientists who don't use this model and think there is something better? Of course. Does that mean we should not "believe" the General Relativity model? No. Science isn't about believing. It's about building models.

There is indeed a scientific consensus that the Earth is warming due to additional carbon dioxide in the atmosphere, and that it is the result of human activity.

Science is all about models

Cox does an excellent job emphasizing the model building nature of science. I think "scientific model" is the best term to use when discussing the nature of science (and here are three scientific words everyone should stop using).

But what is a scientific model? It's just like any other model. Think of a 1:24 scale model of a Corvette. It has many of the features of a Corvette, but it is not a Corvette. It represents a Corvette. A scientific model is the same idea. It is something scientists use to represent the real world. There are many kinds of models:

Conceptual

Physical

Mathematical

Computational

These are the most common types seen in science. They are evidence-based, and can be used to make predictions (like future global temperatures). Models aren't permanent. If scientists find new data that disagrees with the model, they change the model. Here is an example of how the model of the atom changed over time.

Oh wait, you say. Does this mean I am saying the climate model is wrong and will change in the future? Yes and no. Will it change? Probably. Is it "wrong"? Not really. It agrees with our data and can be used to make predictions, so it's still useful. Consider the gravitational model. Your physics textbook probably says gravitational force is equal to mass multiplied by the gravitational field (9.8 N/kg). This is of course wrong. Gravity isn't constant. It decreases in magnitude with distance from Earth. But this wrong model is still very useful. And so is our climate model.

1 Update, 8/18/2016, 11:50 am ET: This article has been updated to reflect the fact the the video clip was originally from the Australian Broadcasting Corporation that was then reproduced with permission for the BBC.