A tree only grows on land. That excludes 70% of the earth covered by water. A tree does no grow on ice. A tree does not grow in a desert. A tree does not grow on grassland-savannahs. A tree does not grow in alpine areas. A tree does not grow in the tundra We are left with perhaps 15% of the planet upon which forests grow/grew. That does not make any studies from tree rings global, or even hemispheric.One must admit though, that the sheep herders who have perpetuated the Global Warming scam really had a good run ... amazing when you come to think of it. But really, how hard is it to herd sheep?
Tree Rings in Their Heads
... that's about all that believers in Mann have: