Climate change causes children to shrink

  • 08 Dec 2011, 17:30
  • Robin Webster

The climate data analyst Tamino, author of the blog Open Mind, has posted a clever deconstruction of a popular climate skeptic argument on his blog Open Mind.

The blog begins

Suppose, just for argument's sake, that when your son Johnny turned 2 years old you decided to monitor his growth. His birthday is Jan. 1, so on the first of every month you measure his height - you even mount a tape measure permanently on the wall so you can measure him in the same location each time.

The topic alluded to is temperature rise, and the ways in which data is misrepresented and manipulated by those who wish to argue that temperatures are not going up - or ' global warming has stopped'.

We've explained why this argument is statistically and scientifically flawed here, but Tamino has a lot more fun with it. In his analogy, parents measure their son, and in October of his third year, they plot his height as a function of time:

Screen Shot 2011-12-08 At 17.55.59


"?!?!?" says the father. His wife thinks there must be some mistake...

But you're [you're the dad, by the way] still worried. So you consult your next-door neighbor, who happens to work with the Global Warming Policy Foundation, and show the data to him. He declares, "Your wife must have some pro-growth political agenda. The data clearly show that your child is shrinking. You'd better take him to the doctor immediately."

Your wife staunchly refuses to give in to your irrationality. But the next day your neighbor knocks on your door and says, "I can prove that your child is either shrinking, or at least has stopped growing. Look at this graph of his height since age 3 years, 2 months. Over the last 8 months your child has shrunk at a rate of 1.3 cm/yr.

Screen Shot 2011-12-08 At 16.36.20

Your wife interrupts, saying "Please don't be so ridiculous. Obviously the last data point is in error, this photograph proves it." The neighbor retorts, "Even if I leave out the last data point, the recent growth rate is not statistically significant! And the estimated rate is only 1.5 cm/yr, far less than the expected rate of about 7 cm/yr according to the IPCC." (Intergovernmental Panel on Child Care).

Luckily the mother is a bit more switched on. She realises that there are some other complications:

She looks over her photo album. That's when she notices that sometimes when you measured little Johnny's height, he had his shoes on. Other times he was barefoot. Fortunately, since she photographed all the measurements she knows when he was barefoot and when he was shod. She carefully measures the thickness of the soles of his shoes at 2 cm. This, she says, is an exogenous factor which has nothing to do with his actual growth, it just causes random fluctuations in the measurements.

She also enlarges her latest photo (she has all the digital images) and is able to read the correct height from the image - those Nikon cameras are awesome!

Take a look at Tamino's blog for the end of the story . Suffice to say the neighbour isn't impressed with the end result.

Tamino's commenters have also weighed in with helpful advice for the parents:

Obv. fake. Has there been any statistically significant growth in the last four months? Also, does your measure of statistical significance take into account that the nature of the noise is red; Johnny grows or shrinks randomly but from his previous height? In addition, Johnny may experience cyclic growth and shrinkage.

I just think you're being alarmist. There's no reason to buy larger clothes for Johnny and I feel you'd need 10 years more data to say anything about the issue

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