As Michael "Piltdown" Mann taught us, tree rings are the gold standard proxy of global temperatures, because nothing affects the rate of tree growth besides global temperatures. </sarcasm>
This Eastern hemlock was felled in the deep woods in 2013, and shows the folly of using tree rings as a proxy of global temperatures.
This tree grew in woods that is logged every 30 years or so. Logging is this area means removal of any tree over roughly a foot in diameter, leaving smaller trees to grow. The area where the tree grew was logged in 1946, 1983, and 2013, for paper pulp for a mill in Glens Falls, NY.
In 1959 the tree was a sapling. Because the land had been logged in 1946, there was enough sunlight reaching the ground that the tree grew steadily, but it grew slower and slower during the 60's and 70's as larger trees began to overshadow it and more and more block the sunlight, until by the early 1980's the tree was barely growing at all as hardly any light was reaching down to the small tree. Tree rings were under 1/32 inch each by then, and decreasing every year.
In the summer of 1983, loggers removed large trees near the hemlock, allowing the sunlight in. Growth of the tree suddenly shot up, so that the rings were up to 1/4 inch thick until 2013 when the tree itself was felled.
The size of the tree rings was determined entirely by the amount of sunlight reaching the tree, and had absolutely nothing to do with climate, weather, rain, drought, global temperature, or even alarmingly unprecedented global CO2 levels.