A new paper is generating a lot of press with the typical "unprecedented" warming not seen in this case nearly in 44,000 years, though the authors did notice a 5,000 year old "precedented" warming. The temperature proxy in this case was moss of the reindeer snacks variety. The cause is of course CO2 since that is the only "simple" explanation.
The story goes that some 11,000 years ago
the summer sun that shines on Baffin Island near Greenland was 9% warmer
than it is today. That is because the Earth has a little tilt and an
elliptical orbit that causes the stronger currently winter sun, being
closer this time of year in the Southern Hemisphere to switch to
stronger in the northern hemisphere in another ~11,000 years. In about
5,000 years the Southern Hemisphere Spring will be warmer than Fall
while Northern Hemisphere Fall will be warmer than the Northern
Hemisphere Spring. This causes roughly four standard seasonal modes and
mankind has only been taking notice of a portion of one so far. The
paper ignores the more subtle Spring/Fall modes and just concentrates on
the NH hot, NH not so hot modes.
Baffin Island location near Greenland means its climate is inspired by
the North Atlantic portion of the ThermoHaline Circulation (THC) which
gets much of its flow from the Southern Hemisphere's Antartic
Circumpolar Current (ACC). This causes the North Atlantic SST
temperatures to be out of phase with the general glacial mass of the
high northern latitudes.
The four precessional "modes"
plus the ACC out of phase lag produces fairly regular "pulses" in
Global Climate likely stimulating Bond Events
every 1470 +/- 500 years noted in NH ice cores and in the tropics and
Southern Hemisphere orbital harmonics of ~4000 years, 5000 years and
5800 years depending on the lead/lag of the Bond Events relative to the
precessional four mode pulses.
data leaves a lot to be desired, but these two reconstructions of the
sub-tropical North Atlantic and the extra-tropical northern hemisphere
fairly well show the Bond Events and one of the precessional "pulses"
noted as the 5ka Moss zone. Notice how the sub-tropical North Atlantic
was cooler prior to the 5ka Moss pulse.
de Menocal et al. goes back to ~21,000 BC with one hiatus making it
hard to see the "pulses", but around 7000 BC there was another pulse
with a drop following. So from the 5ka moss pulse back at least another
10,000 years there would not have been any other Baffin Island ice loss
likely due to ACC influences. Higher solar irradiance could, but if
the snow/ice is clean, it would tend to reflect most of the solar
So while I am sure that the mother of the
paper's author would be proud of the effort, it is a bit hard for me to
swallow the magical leap to CO2 done it without at least addressing why
there is a Baffin Island Moss Barrier that tends to agree with more
complex "Global" dynamics and Bond Events than his over simplification.
The data made available by the authors noted on the charts can be downloaded at NOAA/Paleoclimateology