A curmudgeons take on rapid climate change

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A curmudgeons take on rapid climate change
Heinrich events massive discharges of icebergs
into North Atlantic Dansgaard-Oeshger
events Large abrupt warmings in Greenland
(10oC in 50 years)
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1. There are connections between the hemispheres
Longer, larger excursions appear to be associated
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1. There are connections between the hemispheres
- longer, larger excursions appear to be
associated - no strong evidence that abrupt
changes are related
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2. There are suggestions that rapid events in
Greenland are apparent elsewhere in the
Northern Hemisphere
Cariaco Basin
But a lot of non D/O variability
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2. There are suggestions that rapid events in
Greenland are apparent elsewhere in the
Northern Hemisphere
Santa Barbara
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3. There is no strong evidence that Heinrich
events are causal (but this does not rule it out)
Did H-events just tend to happen during cold
periods in N. Atl.?
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4. Evidence of changing ocean structure during
glacial/Heinrich (but how strong is this?)
modern
glacial
Heinrich
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5. Weak evidence of changes in overturning rate,
but what is to be expected? i.e. can a shoaling
of NADW be related to reduction in mass
circulation?
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6. Evidence of lots of non-Heinrich related
variability in ocean 13C
North Atlantic 13C
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6. Evidence of lots of non-Heinrich related
variability in ocean 13C
Equatorial Atlantic
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6. Evidence of lots of non-Heinrich related
variability in ocean 13C
South Atlantic 13C
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• 7. Some questions.
• - What is the natural variability of ocean
  circulation to random
• climate forcing?
• - Given non-Heinrich or D/O related variability,
  how likely is that
• these events cause critical thresholds (e.g. in
  sea-ice) to be
• exceeded?
• - How come the largest ocean forcing (Heinrich
  discharges)
• have the least impact on climate?
• Timescales of events (gt1000 years) appear to
  require the
• ocean, but two options
• Passive role of memory - storing perturbations,
  shifting of water masses.
• ii) Active role - dynamics transmits/creates
  climate signal
• How do we (can we) differentiate between these
  two?