Milankovitch Cycles

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Milankovitch Cycles
(Images from Unversity of Montana geology
department website)
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Vostok ice core record (from US global change
research program website)
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Rate of Change of Ice Volume vs. Orbital
Parameters?
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• SPECMAP assumes ice volume is related to orbital
  forcing and is tuned as such.
• HW04 is independent of tuning for orbital
  factors. (Roe 2006)
• SPECMAP plotted with 6kyr lag, HW04 with 8kyr
  lag.
• Vertical units are scaled (and insolation
  reversed)

Figure 1
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• SPECMAP has no lag, HW04 has only 1kyr lag.

Figure 2
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• Linear regression of precession obliquity
  massaged onto insolation (allowances made for
  amplitude and lag)
• Vertical axes scaled. (Also, note different scale
  between SPECMAP and HW04)

Figure 3
SPECMAP
HW04
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Atmospheric CO2 has also been suggested as
driving changes in global ice volume . . .
Comparisons of the impacts of shortwave and
longwave radiative forcing appropriate over the
ice sheets are not straightforward, but taking
summer half-year insolation variations in
shortwave (Fig. 3), and assuming an albedo of 0.5
for melting ice, variations in summertime
shortwave forcing exceed the direct CO2 radiative
forcing by about a factor of five. (Roe 2006)
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• Negative Phase value indicates CO2 signal lags
  behind rate of change of ice volume.
• Vertical bars indicate obliquity and precession
  orbital periods.
• Grey area represents 95 confidence interval for
  Phase range.
• Note cross-spectral coherence at orbital periods,
  CO2 variations lag dV/dt.

SPECMAP (Figure 4)
HW04
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Anthropocene?
Human induced effects on climate?
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Vostok ice core record (from US global change
research program website)
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• CO2 follows expected pattern until 8000 years
  ago.
• CO2 should actually be higher, to include amount
  that compensates for decrease expected of an
  interglacial cycle.

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Proposed major cause Land Clearance.

• Estimated total Carbon from deforested areas by
  2000 yrs BP 224249 Gt
• Target amount by 2000 yrs BP for hypothesis 255
  Gt

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Supporting evidence Plagues!
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• Only plagues can affect enough of the human
  population on the regional scale over a short
  time interval.
• The largest epidemic in history was the Black
  Death in the Middle ages (1347-1377AD).
  Mortality rates reached up to 50 in many
  regions. The timing of this plague matches a
  10ppm drop in CO2 seen in the Taylor Dome ice
  core record.
• Mechanism is likely to be (must be?) carbon
  sequestering during re-growth of forest on
  abandoned farms and villages models show this
  land can return to full carbon capacity in as
  little as 50 years.

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• Baffin Island dead lichen from failed glaciers.
• 2 ?C warming in Northern Canada has prevented
  glaciation event 6000 years ago, as predicted by
  Milankovic forcing.
• Offset glaciation?

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STOP GLACIATION!