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The mainstream reporting of cliamte science is cataching up with something I've known for some time – that there is warming that is already implicit with present levels of greenhouse gasses
New Study Finds that Present CO2 Levels are Capable of Melting Large Portions of East and West Antarctica
1
August, 2017
If
you’re a regular reader of this blog and its comments section,
you’re probably more than a little worried about two bits of
climate science in particular:
Our
understanding of past climates (paleoclimate) and 5-6 C long term
climate sensitivity.
And
if you’re a frequent returner, you’ve probably figured out by now
that the two go hand in glove.
******
Looking
back to a period of time called the
Pliocene climate epoch of 2.6 to 5.3 million years ago,
we find that atmospheric carbon dioxide levels were somewhat lower
than they are at present — ranging from 390 to 400 parts per
million. We also find that global temperatures were between 2 to 3
degrees Celsius warmer than 1880s ranges, that glaciers in Antarctica
and Greenland were significantly reduced, and that sea levels were
about 25 meters (82 feet) higher than they are today.
(The
Totten Glacier is one of many Antarctic land ice systems that are
under threat of melt due to human-forced warming. A new paleoclimate
study has recently found that levels of atmospheric greenhouse gasses
that are below those presently in our atmosphere caused substantial
Antarctic melt 4.23 million years ago. Image source: antarctica.gov.)
Given
that atmospheric CO2 levels during 2017 will average around 407 parts
per million,
given that these levels are above those when sea levels were
considerably higher than today, and given that these levels of heat
trapping gasses are rapidly rising due to continued fossil fuel
burning, both the present level of greenhouse gasses in the Earth’s
atmosphere and our understanding of past climates should give us
substantial cause for concern.
This
past week, even more fuel was thrown onto the fire as a
paleoclimate-based model study led by Nick Golledge has found that
under 400 parts per million CO2 heat forcing during the Pliocene,
substantial portions of Antarctica melted over a rather brief period
of decades and centuries.
Notably,
the model found that the West Antarctic Ice Sheet collapsed in just
100-300 years under the steady 400 ppm CO2 forcing at 4.23 million
years ago. In addition, the Wilkes
Basin section
of Antarctica collapsed within 1-2 thousand years under a similar
heat forcing. In total, the study found that Antarctica contributed
to 8.6 meters of sea level rise at the time due to the loss of these
large formations of land ice.
We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points (emphasis added).
This
study began the publication process in 2016 when year-end atmospheric
CO2 averages hit around 405 parts per million. By end 2017, those
averages will be in the range of 407 parts per million. Even more
worrying is the fact that CO2 equivalent forcing from all the various
greenhouse gasses that fossil fuel burning and related industrial
activity has pumped into the atmosphere (methane, nitrogen oxides,
CFCs and others) will, by end 2017 hit
around 492 ppm.
As
a result, though conditions in Antarctica are presently cooler than
during 4.23 million years ago, the considerably higher atmospheric
greenhouse gas loading implies that there’s quite a lot more
warming in store for both Antarctica and the rest of the world. A
warming that, even if atmospheric greenhouse gasses remain at present
highly elevated levels and do not continue to rise, could bring about
a substantially more significant and rapid melt than during the
Pliocene.
Links:
Hat
tip to Spike
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