Hello,

That's a very interesting question, but I think it probably lies outside the areas of expertise of most of us here at Solar Week. I've heard of scientists looking at proxies for solar data before, but I don't know a lot about it so I had to look on the Internet.

From what I could find, it looks like some of the proxies for solar activity data are more quantitative than others. Historical records describing auroral observations at low and mid-latitudes and naked-eye sunspot observations can be used to provide clues to the times of solar maximum for solar cycles in the distant past. I would say that these types of proxies are rather qualitatitve in nature. One way historical records can be validated is to find independent accounts from several different observers of the same phenomenon.

Some of the more quantitative proxies for solar activity data are the concentrations of certain radioactive isotopes of carbon and beryllium in Antarctic ice cores. Radioactive isotopes of beryllium are produced by interactions between cosmic rays and the Earth's atmosphere. According to an article I found, beryllium 10 retrieved from ice cores is one of the best indicators of solar activity over the past tens of thousands of years. Also, examining the concentrations of carbon dioxide in ice cores can help us learn about the past amounts of this greenhouse gas in the Earth's atmosphere. Tree rings provide another source of data about the Earth's climate in the past.

I didn't find anything about how they validate these proxies for solar and climate data during my quick Internet search, but I can make an educated guess at how they do it. For studies using radioisotopes, scientists probably look at the decay rates of these materials and extrapolate trends in cosmic ray flux data back as far as they can. Scientists also probably compare measurements of the radioiostope concentrations made from samples taken at different sites. Comparing the trends in the Earth's climate obtained from two different types of data, for example ice cores and tree rings, is probably another way to validate these data sets. I am sure that scientists also compare these quantitative data sets with historical records whenever possible.

You can learn more about Antarctic ice cores here:

http://www.aad.gov.au/default.asp?casid=34675

http://antarcticsun.usap....thandler.cfm?id=1491

Kris