Drunken trees

[1][2] This commonly occurs in northern subarctic taiga forests of black spruce (Picea mariana) under which discontinuous permafrost or ice wedges have melted,[3][4] causing trees to tilt at various angles.

[5][6] Tilted trees may also be caused by frost heaving,[7] and subsequent palsa development,[8] hummocks,[9] earthflows,[10][11] forested active rock glaciers,[12] landslides, or earthquakes.

[21] The reaction wood formed by this process can be studied using dendrochronology using annual growth rings to determine when the tree was subjected to tilting.

[31][32] Al Gore cited drunken trees caused by melting permafrost in Alaska as evidence of global warming, as part of his presentation in the 2006 documentary film An Inconvenient Truth.

Similar warming leading to permafrost thawing in neighboring Siberia has been attributed to a combination of anthropogenic climate change, a cyclical atmospheric phenomenon known as the Arctic oscillation, and albedo positive feedbacks caused by both when melting ice exposes bare ground and ocean which absorb, rather than reflect, solar radiation.