You forgot one very important variable- rain. A year might have heavier than average rain and be warmer than average but it might instead be colder than average. I see no way to distinguish those scenarios from centuries ago without a matching historical record - regardless of how many trees are sampled. Perhaps other temperature proxies might accurately indicate past temperatures but I doubt tree ring analysis can do that. Since climate change science needs accurate data, just how accurate do tree ring reserachers claim this data is? Joe Zorzin (forester with 47 years experience)