Anecdata: my favorite new word

Anecdata are all around us. They are stories and observations that people use to prove what they want to prove--or at least to believe what they want to believe.

I live in Maine, where the sea levels are rising. According to the anecdata, the seas have risen so much over the last decade, that people can see the difference. Sadly, the instruments that scientists use to measure sea levels are not as accurate as peoples' observations.  Here's data collected in Bar Harbor. 

That's 0.62 feet per hundred years.

That's less than an inch per decade. I don't know about you, but I don't think that I can detect a one inch per decade tidal change when the high water mark changes so much with the phase of the moon.

OK, maybe Bar Harbor's an outlier. Let's try Portland. 

Sorry, Portland's average sea level rise is even lower that Bar Harbor's

OK, maybe it's not so bad, but maybe it's getting worse. 

Let's look at longer-term trends, say over 50 years periods.

Well, that's Portland. Maybe it's an outlier. Let's try Halifax. Ooops. Same trend.

Here's what the big picture looks like. Green means less than a foot per century. Most places are green. Yellow means 1-2 feet per century. The mid coast of the US is yellow.

How can some sea levels rise a foot per century and others two or even three? How can some places (like Alaska, not shown) actually experience falling sea levels? The answer is that all the world's seas are rising at about the same rate: less than a foot per century. And in some places, land is rising or falling and that makes the difference.

So anecdata tells some people something different from what the world's instrumental data shows. Sea levels rising. Anyone who says they are not is an idiot. 

But they are rising slowly. And apparently the rise is not accelerating.

Not accelerating yet, I imagine some people saying. Not yet. And they are right. But they're not falling, yet, either.

Fact is, we don't know. We can speculate, and we can model, but neither speculations nor models are knowledge.

I'd bet on accelerating before I'd bet on falling. But I'd put most of my money on continuing the current trend.