By Nir Shaviv, Science Bits

One of the “scientific” highlights in Al Gore’s movie is the discussion about the clear correlation between CO2 and temperature, as is obtained in ice cores. To quote, he says the following when discussing the ice-core data (about 40 mins after the beginning for the film): “The relationship is actually very complicated but there is one relationship that is far more powerful than all the others and it is this. When there is more carbon dioxide, the temperature gets warmer, because it traps more heat from the sun inside.”

Any laymen will understand from this statement that the ice-cores demonstrate a causal link, that higher amounts of CO2 give rise to higher temperatures. Of course, this could indeed be the case, and to some extent, it necessarily is. However, can this conclusion really be drawn from this graph? Can one actually say anything at all about how much CO2 affects the global temperature?

To the dismay of Al Gore, the answer is that this graph doesn’t prove at all that CO2 has any effect on the global temperature.  The main evidence proving that CO2 does not control the climate, but at most can play a second fiddle by just amplifying the variations already present, is that of lags. In all cases where there is a good enough resolution, one finds that the CO2 lags behind the temperature by typically several hundred to a thousand years.

Analysis of ice core data from Antarctica by Indermühle et al. (GRL, vol. 27, p. 735, 2000), who find that CO2 lags behind the temperature by 1200±700 years.

See more in this excellent blog here.