Tuesday, August 06, 2013

Occam's Razor and Anthropogenic Global Warming

William of Ockham (1287-1347) taught that of competing hypotheses, the simplest hypothesis with fewest assumptions should be chosen.

There are two competing hypotheses regarding anthropogenic (man-made) global warming.

One is that it is serious, and the other is that it is not.

The serious, mainstream science view goes like this:

  1. The greenhouse effect is real. Without it, average surfact temperatures would be -15C, not +15C
  2. CO2 is a greenhouse gas
  3. CO2 levels have increased by 41% since pre-industrial times
  4. A 100% increase will cause a 1.2C rise in earth surface temperatures
  5. This rise will in turn cause a 3C (+/- 1.5C) rise in surface temperature.
    Explanatory video on this point here 
  6. Any rise above 2C must be avoided
Reasonably simple, given the vast complexity of our planet's climatic system, and in fact the handful of serious climate scientists on the "sceptic" side agree with points 1-4.

Now here is the climate "sceptic's" case:
  1. The earth is not warming
  2. If it is warming, it is due to the sun
  3. The warming is due to some kind of natural variation
  4. It's going to get cooler soon
  5. CO2 is too tiny to make a difference
  6. CO2 will make a difference but there's nothing we can do about it
  7. We can afford to wait another 10-50 years to see if it is going to get hot then do something about it then
  8. It is going to warm but only a bit
  9. CO2 is good for us
  10. Cloud cover will extend in a warmer planet and cool us down (No it will not)
  11. All models are always wrong
  12. Some models show that the climate will not warm much
  13. It is all a conspiracy by climatologists, Greens, the nuclear industry and the UN
  14. It cannot be happening because it would mean that fossil energy would become unprofitable
  15. It is cold outside today
  16. Heat cannot get into the ocean
  17. And so on
  18. And so forth
What the above shows is that there is an endless complexity to the arguments brought by the "sceptics", many of them self-contradictory. 

They are not trying to present a coherent picture of reality, which is the aim of science. They are merely producing a stream of counter statements. I have been impressed recently that when I try to discuss the one point where agreement exists with a delayer, they rapidly change the subject to find disagreement. 

In fact, their case often boils down to a mirror image of the case for man-made global warming. If we say white, they just say black. 

I predict therefore that soon "sceptic" blogs will be quoting William of Occam as evidence for the truth of their case.

[This topic tackled from a slightly different angle by the excellent Dr Boli.]

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