A Few Things Ill Considered

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

Objection:

Climate is an inherently chaotic system, and as such it can not be predicted.

Answer:

Firstly, let's make sure we define climate. Climate is generally viewed as an average of weather patterns over some meaningful time period. The number of years may vary and there are probably plenty of other finer points to quibble about in there, but the purpose of getting this definition out in front is to be sure we are safe in discounting the very chaotic looking annual flucuations of global mean temperature. This is weather, and one or two anomalous years does not represent a climate shift.

Now, I know that quite a few people believe that climate is a chaotic system, and maybe on some large scale levels, it is. But it is not chaotic on anything approaching the kinds of time scales humans need to be mindful of. Frankly, I have never heard any objective argument supporting that notion, only arguments that take that as a given. Certainly the march of the seasons is nice and regular, and determined directly by the orbital inclination of the earth. If a large volcanic eruption occurs, the global temperature drops for a few years quite predictably. Diurnal cycles show the very direct influence of insolation changes on the system. Clearly, if you turn down the sun, the temperature drops. Clearly, if you throw a bunch of SO2 into the stratosphere, the temperature drops. Clearly, if you turn the surface completely white, the temperature drops. And clearly, if you double the amount of an important GHG in the atmosphere, the temperature rises.

What about longer timeframes? One can also look at the glacial/interglacial cycles. These cycles are by no means perfectly regular but they are also clearly far from random. They are also a broadly deterministic effect following a known cause: orbital variations. I will grant you that the data is quite chaotic on the multi-century time scale even as it clearly follows a 120Kyr cycle, but who is to say that had we enough data and understanding, these spikes and dips could not be thoroughly explained by solar infuences, volcanic eruptions, greenhouse gas changes, ice sheet dynamics etc?

The ocean-atmosphere climate system is indeed a complex system and is capable of some surprising behaviours, but there is no evidence that it is chaotic and I see no problem with speaking in a meaningful way about future expectations. Model outputs do in fact produce specific year to year fluctuations, fluctuations that are not hindcasted well (that is the weather after all), but I don't think anyone is that interested in knowing the exact temperature of any particular year, it is the decadal and century trends that we want to anticipate.

It is the climate's broadly deterministic response to forcings that are of interest, and all evidence points to such determinism.

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

"Chaotic Systems are not Predictable" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.