Source: Muddy Japanese lake offers spectacular prospects for carbon dating With all the chatter about trying to find proxies for temperature, it is great to read a study that helps calibrate a scale. Bob Wilson
You may not have been saying so, but c14/c14 is not used as a temperature proxy. It is the primary dating tool for things up to 30,000 years old, which is about 6 half lives. The linked article says 60,ooo years or 12 half lives, and they will have to do some sharp work with the accelerator mass spectrometer to go back that far. The first calibrations were done with C standing A/NV bristlecone pine trees, which can live for more than 2000 years and have annual rings that can be visually counted. Much longer records like those here are rare. At least in the sense that people have not found them yet. Before the Atomic Age, 14C variation in the atmosphere was completely controlled by solar output. So it is a proxy for that, and to the extent that solar output affects earth air temperatures, yeah you could make a case for it being a T proxy. But when CO2 was lower, earth orbital variation appears to have been the strongest T forcing. Now with more CO2, infrared absorption seems to prevail over solar variation, volcanic emissions, and all those other things.
