Climate Change

tater · 04-02-10, 10:12 AM

BTW, regarding the notion of "average temperature" that one might get from ice cores—it's not an observation, but a calculation. It is a value derived from proxies by assumptions, and is not a direct measurement. Ten people with ten assumptions could get differing temps from the same data. Calibration to the present might, or might not mean good calibration with periods farther back depending on the model. I'm quite wary of over generalized conclusions.

Even modern "average temp" is a calculated value. Weighted, too. It's not like someone takes a giant thermometer and shoves it in Bangladesh (or wherever the ******* of the Earth actually is) and gets a temperature measurement. Even satellite data has to be manipulated to provide such a figure—how does one weight over land vs ocean, does the satellite cover the whole earth, or does it miss certain regions due to orbital inclination?

So the notion of some long term global average temp is somewhat silly, IMO, particularly when the proxy is ice cores. What IS the proxy there, are they using layer thickness (what if the ice melted one year?)? Are they using dissolved CO2—doesn't that require assumptions about CO2 absorption leading or following warming (there are reasonable arguments that dissolved CO2 is released as a response to ocean warming, for example)? Tree ring proxies have certainly been troublesome statistically (they basically throw away any data that doesn't support their conclusion instead of throwing all the data in, and seeing if it works or not).

I'm not saying that a temperature history isn't interesting, but I think that the complexity of the system is such that a "global average" is not terribly meaningful. The average temperature of a star, for example, is similarly meaningless. The core temp is a function of the type of fusion cycle it is running, and the surface temp a function of convection, reradiation, etc. At least that temp is actually observable directly—though the corona is yet another region to look at. Complex systems and the idea of a single number to describe them are an odd combination.

04-02-10, 10:12 AM	#11
tater Navy Seal Join Date: Mar 2007 Location: New Mexico, USA Posts: 9,023 Downloads: 8 Uploads: 2	BTW, regarding the notion of "average temperature" that one might get from ice cores—it's not an observation, but a calculation. It is a value derived from proxies by assumptions, and is not a direct measurement. Ten people with ten assumptions could get differing temps from the same data. Calibration to the present might, or might not mean good calibration with periods farther back depending on the model. I'm quite wary of over generalized conclusions. Even modern "average temp" is a calculated value. Weighted, too. It's not like someone takes a giant thermometer and shoves it in Bangladesh (or wherever the ******* of the Earth actually is) and gets a temperature measurement. Even satellite data has to be manipulated to provide such a figure—how does one weight over land vs ocean, does the satellite cover the whole earth, or does it miss certain regions due to orbital inclination? So the notion of some long term global average temp is somewhat silly, IMO, particularly when the proxy is ice cores. What IS the proxy there, are they using layer thickness (what if the ice melted one year?)? Are they using dissolved CO2—doesn't that require assumptions about CO2 absorption leading or following warming (there are reasonable arguments that dissolved CO2 is released as a response to ocean warming, for example)? Tree ring proxies have certainly been troublesome statistically (they basically throw away any data that doesn't support their conclusion instead of throwing all the data in, and seeing if it works or not). I'm not saying that a temperature history isn't interesting, but I think that the complexity of the system is such that a "global average" is not terribly meaningful. The average temperature of a star, for example, is similarly meaningless. The core temp is a function of the type of fusion cycle it is running, and the surface temp a function of convection, reradiation, etc. At least that temp is actually observable directly—though the corona is yet another region to look at. Complex systems and the idea of a single number to describe them are an odd combination.