“But It’s Been Warmer In The Past!”

Here’s an argument you’ve probably heard n times already:

 

“It was warmer in the past than it is now without CO2 being as high, therefore CO2 cannot be the cause of our current temperature high!”

– Forum troll, ca. 2014.

 

So, now that you’ve heard that argument n+1 times, without any indication of mathematical induction kicking in……let’s think about it for a moment. What, exactly, is being said here? I think my favorite variant on the argument is this:

 

FooReasons to vaccinate, part 403,203,504,202

“Hey, for all we know, the 30-year-war killed them!”

“People died en masse before the black plague, therefore the black plague cannot be the cause of our current dying spree.”

– Forum troll, ca. 1300.

 

Look, here’s a basic climatology lesson for all of you: the earth’s climate is a complex, multifaceted system with several significant factors. Anyone who would tell you otherwise is simply lying to you. And climatologists know this. They’re not stupid; in fact, they generally have as much knowledge in the field of climatology as anyone in the world is likely to have, on account of being climatologists, who have spent years studying in the field, producing peer-reviewed papers, keeping up with the latest information, et cetera. So what are those factors? Well, here are a few:

Forcings: The initial drivers of climate.

  1. Solar Irradiance.
  2. Greenhouse gas emissions.
  3. Aerosols, dust, smoke, and soot.

Climate feedbacks: processes that can either amplify or diminish the effects of climate forcings. A feedback that increases an initial warming is called a “positive feedback.” A feedback that reduces an initial warming is a “negative feedback.”

  1. Clouds.
  2. Precipitation.
  3. Greening of the forests.
  4. Ice albedo. 

…Of course, the article goes into far more detail, and provides sources and whatnot. It also neglects to mention important factors such as specific sea currents, which often provide relatively clear and predictable cycles (ENSO, PDO, etc.), Milankovich cycles, and issues like landmasses shifting (an earth with a lot of landmass around the poles and not a lot along the equator is going to take in solar energy very differently from an earth with nothing at the poles and a lot of land around the equator).

 

But the point I’m trying to get to is this. At any given point, if the Earth is warming, the question should be “why?”. We should be asking ourselves, “why was this period in history warm?”. There are numerous factors which can influence global temperatures; we need to check to see which apply. In the medieval warm period, for example, it turns out that the North Atlantic Oscillation was acting up in an unusual way. It’s not enough to say, as some phenomenally dumb people do (*cough*Monckton*cough*), that the medieval warm period was warmer than today without the same level of CO2, therefore current warming cannot be contingent on CO2. People died en masse in World War II, and World War II was not contingent on drone strikes, but this does not imply that civilian deaths in the war on terror could not be based on drone strikes! The very best you could say is, if we did find a period where temperatures really didn’t match up with our models in the past, is that we don’t know why it was warmer/colder than it should have been at that time, and that our models might be flawed. It does nothing to discredit the current understanding of anthropogenic global warming.

 

See, this is the other crucial flaw with the argument. Beyond the fact that it’s basically meaningless because climate can change based on things other than CO2 (and we’ve known this for quite a while!) and we understand that and we’ve checked for all of the things we currently know about, it’s also meaningless because we are able to directly check the connection between CO2 and temperature. The basic theory was formulated by Svante Arrhenius before 1900 (no, seriously) and the science has only moved forward since then. Anyone who isn’t already clear about this would do well to check out SkepticalScience’s page on the subject, which offers extensive documentation. It wouldn’t matter if there was a temperature change in the past that we couldn’t quite explain. It would have no bearing on the evidence we have today that shows that CO2 is a major driver of climate, and that anthropogenic CO2 emissions are causing the earth to warm. None whatsoever.

 

The argument just fails. And yet you’ll see it all over the place. I suppose the most succinct answer is just to analogize – to show them that just because we don’t know why the neanderthals died out tens of thousands of years ago doesn’t mean we can automatically reject the evidence supporting the “gas chambers” hypothesis for why millions of Jews died in World War II. When people discover that the exact logic they’re using can also be used to deny the holocaust, they usually stop talking. Or, if they don’t, they usually aren’t worth speaking to anyways.