Summer drought; all of the affected trees show a narrower ring. To illustrate this we only have to consider the publication and subsequent withdrawal of two European tree-ring chronologies. Consider that if an animal or plant lived during this time of rapidly increasing carbon levels relative to carbon that different portions of the plant or animal would have different 14 C to 12 C ratios incorporated into these different parts depending upon the rate of growth. Dating of period buildings. These effects seems to limit carbon dates of all organic specimens to less than 43, years. The common explanations given simply do not explain the obviously high levels of 14 C in supposedly ancient organic specimens to my own satisfaction.
The last major glacial advance in America was believed by most scientists to have occurred about 25, years ago.
Dendrochronology: How Tree-Ring Dating Reveals Human Roots
How could this have happened? Studhalter, R. A Fragment2nd ed. However, it is a circular process. Why the significant difference in matches depending on which master was chosen? A fully anchored and cross-matched chronology for oak and pine in central Europe extends back 12, years,  and an oak chronology goes back 7, years in Ireland and 6, years in England.