A New Extended Hockeystick
Shaun Marcott of Oregon State University and his colleagues have made a reconstruction of global temperature for the past 11.300 years, full holocene epoc.
A warm period after last deglaciation was followed by a long cooling trend but finally a sudden temperature rise! Warm conditions until the middle of the Holocene were caused by increasing angle of Earth´s axial tilt after the last Ice Age. Following long term cooling trend was caused by decreasing angle of Earth´s axial tilt leading to a cooler world step-by-step.
Remember: High axial tilt leads to warm summers with increased snow melt and cold winters with less snowfall due to decreased evaporation. Polar ice sheets are shrinking! Low axial tilt leads to cool summers with decreased snow melt and mild winters with intense snowfall due to increased evaporation. Polar ice sheets are extending!
Marcott el al. used diverse land- and marine-based proxy data from all around the world, primarily fossils from ocean sediment cores. O18/O16 ratio (two isotopes of oxygen with different weights) in single-cell Foraminifera calcium carbonate shells is a reliable proxy. It is temperature-sensitive as a result of isotopic fractionation. Heavier O18 is easier to condense out and more difficult to evaporate than O16, as colder as much more (and vice versa).
The curve derived from proxies was calibrated with a global temperature reconstruction from Climate Research Unit (Mann et al.,2008) over a period of roughly 1000 years which the two reconstructions have in common.
Marcott et al. also used instrumental data for temperatures of recent times. There was a sudden uptick in their curve beginning with the epoc of industrialization. Modern global warming is really exceptional!
Michael E. Mann´s classic Hockey Stick is clearly confirmed by this new study.
Jens Christian Heuer
Source: Science, March 2013