Other things can affect tree ring growth besides temperature or even climate. We had a huge spruce broken off about half way up in a storm event. The rest of the tree was allowed to live on until a a heavy, wet snow/ice storm exfoliated it (peeled it apart). When the trunk was cut off, the hundred or so early years of the trees life showed variation, but the last twelve were all very thin. The injured tree had simply not grown as much in the years after the injury. Whether disease, climate, physical injury, dust in the atmosphere or smoke, there are more things than just the weather which will cause variation in tree rings.