Ancient trees contain all types of valuable information. By examining sections of Adonis, scientists can learn a lot about cycles of weather and climate over the last 1075 years. Growth rates can be discerned by the tree rings, and impurities and other problems with the tree can be evaluated based on the year they occurred.
Specialists have to be aware of three things: the color, the length and inner circles from the trunk, and width of the core. With theses variables, specialists can estimate the age of the tree. Other quality variables can infer past climate and weather change but it is a long a process to analyse those.
The discovery of the Millennial Tree in Greece is a great chance for us to get a little more knowledge about the weather patterns from the last thousand years, although I doubt it will give us enough definitive evidence to understand the problem completely. I believe that we already do testing of ice in sort of the same way to "look back" through history to see non-standard events. Regardless, this is a wonderful opportunity for scientists to study weather in Greece specifically.
A single Millennial Tree, termed 'Adonis', that has reportedly survived for more than a thousand years, is unlikely to improve our knowledge of weather and climate. If it were a group of trees, or a whole forest whose trees survived this long, there will be more optimism about it.
There were reports of long-surviving trees in parts of Africa and Asia, where the weather is completely different from Greek's. If these have not told scientists much about the intricacies of climate change, Adonis discovery may not add anything significant.
The cycles of weather and climate are generally more appreciated from the view of Oceanology, the study of oceans, through which scientists attribute the climate change the earth is undergoing.