While some cold regions show evidence of recent decoupling of tree-ring growth from observed temperature rise, i.e. restricted growth increase, similar evidence from other regions is missing. Increasing or diminishing regional coherency in tree growth has also been observed over recent decades.
The temporal and spatial extent of the above-mentioned processes are poorly known and their drivers are not well understood. Pollution and changing climate have often been discussed as a cause of divergent or convergent growth patterns and deviations of growth from driving climatic variable.