Wednesday, December 16, 2009

Reference: Climate change 101, Bangkok Post, December 16, 2009

To establish the idea that carbon dioxide causes global warming, it is claimed that "The notion of warming comes from basic science: Carbon dioxide traps heat." (Climate change 101, Bangkok Post, December 16, 2009). Basic science does tell us that carbon dioxide absorbs heat but that in itself is not enough to conclude that the observed rise in atmospheric carbon dioxide levels has caused global warming. The essential parameter for that relationship is the climate sensitivity of carbon dioxide.

The source of that parameter is not "basic science" but an empirical correlation computed between CO2 and temperature in Antarctic ice core data. However, to use these data in this way is not scientific; first because correlation between historical data does not imply causality; and second because carbon dioxide lags temperature in the data.

The lag shows that during periods of warming, temperature goes up first and carbon dioxide rises later. Therefore rising carbon dioxide levels could not have been the cause of warming. In any case, a correlation between x and y in uncontrolled field data could exist if x causes y or if y causes x or if a third unobserved variable causes both x and y or if the correlation is spurious. To derive causality from such data is bad science.

Cha-am Jamal

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