Cause and Effect in Global Warming

I read Phillip Morrison’s review of Spencer R. Weart’s book, The Discovery of Global Warming , in the June 2004 issue of Physics Today, (page 60). Weart’s book contains four graphics and other evidence that apparently convinces Morrison of global warming’s causes.

There is evidence of increasing global temperatures and increasing atmospheric carbon dioxide concentrations. Morrison is convinced that one causes the other but never mentions whether Weart says which is the cause and which the effect, or whether he gives evidence to support either case. Solid science, though, does support one case.

It is widely known that the largest single repository of CO₂ on Earth is the oceans, and that the solubility of CO₂ in water drops as the water temperature increases. So clearly a mechanism exists whereby increasing ocean water temperatures (which is where most of the solar energy goes) causes increased out-gassing of CO₂ into the atmosphere. Furthermore, Arctic permafrost zones revert to marshy peat bogs when the Arctic warms, and then bacterial activity takes hold and converts decaying ancient vegetation into atmospheric CO₂. Both of those processes are happening right now.

The Russian Vostok ice cores going back 420 000 years and the Dome-C ice cores going back 730 000 years show that the Antarctic ice sheet has not melted during that time frame, even in the warmest interglacial periods. The ice cores also show periods of rapid global warming accompanied by rapidly increasing atmospheric CO₂.

Now we know that our sport-utility vehicles did not cause all those CO₂ increases back then, but we do understand how global warming causes them. So perhaps Weart can tell us conclusively which of the two is the cause and which the effect; the ice cores seem to give us the answer.

By the way, when floating sea ice melts, Archimedes would insist that the level does not change; in particular, it does not go up. That takes care of gravitational energy, but the melting of all that sea ice extracts astronomical quantities of latent heat from the surrounding ocean water and lowers the mean ocean temperature; so the level will go down, not up. And I can suggest a very illuminating experiment for anyone who believes that heat to melt sea ice does not come from the surrounding ocean.