Friday, December 4, 2009

Innumeracy

I happened upon an article discussing glacial retreat and ice melt. At the end of the article there were several ‘glacial facts’. Here are some:
  • Average yearly retreat of the Himalayan glaciers: In 2006, 30 metres;
  • Rate at which Gangotri is melting per year: 28.1 m
  • Gangotri Length: approx 30 km;
  • Year in which Gangotri will disappear: 2050, if glacier melt continues at the same rate.(emphasis mine)
There is an obvious problem here. 30 meters per year times 50 years (1500 meters) is nowhere near the entire length of the glacier (30000 meters). It's a factor of 20 too small. This isn't a rant about climate change, it's a rant that the journalist and the editor didn't notice the problem with the math. I wouldn't expect that the journalist or the editor be wizards at calculus, but this is just a simple estimate. You don't even need an exact answer (I rounded up the melting rate and the time span to make it easy to multiply).
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7 comments:

  1. offby1December 4, 2009 at 10:26 AM

    Yep, frustrating.

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  2. cosmichorrorDecember 4, 2009 at 10:45 AM

    Of course, glaciers don't melt only from the end, they also melt from the top. Possibly the constant rate referred to in the last bullet is referring to something proportional to the surface area of the glacier. As the glacier gets thinner, the linear rate of retreat will increase.

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  3. NathanDecember 4, 2009 at 11:50 AM

    Perhaps the article meant "if the melting rate continues to increase at the same rate". Or perhaps the newspapermen just can't do math.

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  4. Charlie MartinDecember 4, 2009 at 2:03 PM

    the newspaperman is just reading stuff propagating from a typo. Some years ago, someone typo'ed "2350" into "2035" and it's taken on a life of its own.

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  5. UnknownDecember 13, 2009 at 6:31 PM

    Jrm, it's not a linear approximation, it's exponential, each year there's less and less, that rate is proportional to the actual size, next year it will be smaller and the melting rate will be larger, next time get your facts right.

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  6. Joe MarshallDecember 13, 2009 at 9:49 PM

    Ana: I'll grant you that it may be exponential, but the article said “if glacier melt continues at the same rate” Regardless of what is actually going on, the article as written does not make sense.

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  7. UnknownFebruary 24, 2010 at 4:49 AM

    But the rate may be referring to the volume that melts or something like that. It's also quite possible that some of the numbers are approximations, e.g. the length could very well not be adapted to the ground formations underneath whereas the yearly retreat (being of much smaller scale) might be.

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