Tuesday, February 28, 2012

Correlation and Causation

I haven't read geologist Bill McGuire's book Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis, and Volcanoes so I don't want to be unfairly critical, but I do have a couple of questions.

According to an article in New Scientist McGuire cites evidence that "catastrophic outbursts of geological activity accompanied past periods of rapid climate change, for instance, when we shifted in and out of ice ages."

But he concludes from this (again, according to the New Scientist article) that:
The stresses and strains of rising and falling sea levels and the creation and loss of ice sheets triggered these outbursts. Climate change, he says, may already be shaking up the Earth anew.
My question is that if we accept the claim that climate change and geological activity are historically correlated, how does that justify the conclusion that climate change caused the geological activity? What evidence precludes the possibility that the reverse was the case, that increased geological disturbances like vulcanism, which spews massive amounts of greenhouse gasses into the atmosphere, caused climate change?

The article continues with this:
During the last ice age, the weight of ice suppressed volcanic eruptions. When the ice melted the land surface lifted, sometimes by hundreds of metres, reducing pressure below and turning solid rock to liquid magma. The pent-up rage of the Earth was released. As the ice age faded, the number of volcanic eruptions grew 50-fold. Global warming threatens a reprise.
That's a plausible account of what could have happened, but no more plausible to my untutored mind than the possibility that increased volcanic activity produced the climatic changes that melted the glaciers.

New Scientist closes this unfortunate piece with a bit of unscientific nonsense:
It could be that something is afoot. Six years ago, McGuire suggested shrinking glaciers in New Zealand's Southern Alps might trigger an earthquake. Cue Christchurch [earthquake]last year.
In logic this is called the post hoc fallacy: Just because one event follows another it's assumed that the second event was caused by the other. It's the same sort of reasoning resorted to by astrologers: Ten years ago there was a conjunction of Mars and Jupiter and today Jeremy Lin is an NBA sensation, ergo the conjunction must have caused Lin's emergence as a superstar.

The final sentence is this:
The climate, we know, has been unusually stable in the past 10,000 years. That meant the world was more geologically stable as well. Now, as we face future climate chaos, we may also face geological mayhem.
Or, of course, we may not, who knows, but being scientifically accurate, sticking to the evidence, and being responsible wouldn't be as much fun as throwing a gratuitous scare onto the table.