Download Is there a credible upper bound for global sea level rise

Is there a credible upper bound for global
sea level rise and can we live with it?
Chaos in a changing climate
Chaos and Complex Systems Seminar
UW-Madison, January 27, 2009
Philip Keillor
[email protected]
Differing perceptions of chaos
• “Chaos is the score upon
which reality is written.”
• …Henry Miller, American
writer
“Reality is the score upon
which chaos is written.”
…Philip Keillor, American
coastal engineer
My intent for this seminar
• 1. talk about chaos in the climate system…and
abrupt climate change
• 2. focus on some chaotic elements that may
affect sea level rise
• 3. show you a wish list for recommendations on
extreme sea level rise
View of a climate modeler:
• “Climate can vary chaotically, i.e., in the absence
of any forcing. Indeed, the climate system
exemplifies ‘complexity’, a combination of
deterministic behavior and unpredictable
variations (‘noise’ or ‘chaos’)
• Hansen et al, 1997
Hansen, et al 1997
Hansen et al, 1997
Comparison of observed and modeled
climate change: 1979-1996
(Hansen et al, 1997):
• “Observed climate changes contained
unambiguous signatures of both natural and
anthropogenic climate forcings.”
• “Year-to-year climate changes at middle
latitudes…are primarily chaotic functions.”
Abrupt Climate Change (NRC 2002)
“…when the climate system is forced to cross
some threshold, triggering a transition to a new
stat at a rate determined by the climate system
itself and faster than the cause.”
• “…one that takes place so rapidly and
unexpectedly that human or natural systems
have difficulty adapting to it.”
Abrupt Climate Change (NRC 2002)
• “…surprising new findings that abrupt climate
change can occur when gradual causes push
the earth system across a threshold”
• “Chaotic processes in the climate system may
allow the cause of such an abrupt climate
change to be undetectably small.”
A brand new definition of abrupt climate
change (USCCP 2008):
• “A large scale change in the climate system that
takes place over a few decades or less, persists
(or is anticipated to persist) for at least a few
decades and causes substantial disruptions in
human and natural systems.”
Dangerous climate change gets public
attention
• Feb. 2005. U.K. DEFRA’s International Symposium
on Stabilisation of Greenhouse Gas Concentrations,
Avoiding Dangerous Climate Change
• July 2005. Tony Blair’s main agenda item at G8
Summit.
• May 2006. David Attenborough hosted a two part
series; “Climate Chaos” on the BBC
• 2006. Al Gore’s widely-acclaimed documentary and
book: Inconvenient Truth
Chaos Found in IPCC 2007
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nonlinearities,
climate feedbacks,
internal climate variability,
tipping points,
thresholds,
possibilities of abrupt climate changes
Some places to look for chaos in climate
changes
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1. hydrologic cycle
2. flow of the Gulf Stream
3. release of trapped methane
4. ecosystem changes
5. human systems changes
More places to look for chaos in climate
changes
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6. the global carbon cycle
7. clouds
8. aerosols
9. ocean wind patterns and currents
10. rapid polar glacier melting
11. changes in albedo
A bottom line on climate feedbacks:
• “The large response of the climate system (to
orbital forcing) implies a strong amplification of
this forcing.”
• IPCC 2007
My second point:
The problem of extreme global sea level rise
• “Because understanding of some important
effects driving sea level rise is too limited, this
report does not assess the likelihood, nor
provide a best estimate or an upper bound for
sea level rise.”
• (IPCC 2007)
More problems with extreme global sea level
rise
• The long term rise in sea level (beyond 2100)
will be made “significantly larger” by the
breakdown of the West Antarctic and/or
Greenland ice sheets. In Greenland, …this is
likely to happen by 2100 under the A1B
scenario…This questions both the long-term
viability of many coastal settlements and
infrastructure…and the current trend of
increasing human use of the coastal zone…This
issue presents a challenge for long-term coastal
spatial planning.”…………..IPCC 2007
Prospective global sea level rise (meters)
an “apples and oranges” comparison
Rise
Cond.
Ice loss? End Date Source
0.3 - 0.6 BAU
No
2090-99 IPCC 07
>> 0.6 BAU
Yes
2090-99 IPCC 07
Rahmstorf 07
0.5 - 1.4 dh/dT
No
2100
Hansen et 07
<5
Nonlin.R. No
2100
Delta C. 08
0.7 - 1.3 N.A.
?
2100
Delta C. 08
2–4
N.A.
?
2300
Pfeffer et 08
0.8 - 2
Glacial
Yes
2100
Rohling 08
0.5 – 1.5 Paleo.c. Yes
2100
USCCSP 08
>> 0.6 BAU
Yes
2100
One outlook for abrupt climate change
(IPCC 2007)
• “Abrupt climate changes…are not considered
likely to occur in the 21st century…However, the
occurrence of such changes becomes
increasingly more likely as the perturbation of
the climate system progresses.”
• (a modeling-limited outlook)
An outlook for edges of polar ice sheets
(USCCSP 2008)
• About recent, rapid changes at the edges of
•
polar ice sheets:
“It is unclear whether this imbalance is a shortterm natural adjustment or a response to recent
climate change, but processes causing
accelerations are enabled by warming, so these
adjustments will very likely (90% probability)
become more frequent in a warmer climate.”
• (an observation span-limited outlook)
My third point. Desired recommendations on
extreme sea level for planning purposes
• In feasibility studies for coastal projects,
“consider the high probability of accelerated sea
level rise” and “strategies that would be
appropriate for the entire range of uncertainty.”
• NRC 1987. Responding to Changes in Sea Level,
Engineering Implications
My wish list for estimates by others of
extreme sea level rise
• Consider new (or adjusted) “story lines” of a
future world with greenhouse gases and
changed regional and global temperatures
• Obtain best professional judgment of scientists
on conditions likely to trigger polar ice sheet
collapse
• Provide critical review of published estimates of
rates and amounts of sea level rise
A Faith Statement Amid Chaos and Climate
Change
• “It is important not to be fatalistic about the
threats posed by abrupt climate change.”
• ………NRC 2002
My observation and hope
• The short time spans of observations and the
shortcomings of models presently contribute to a
comfortable blanket of uncertainty that shields
us from a clear view of future climate.
• Perhaps chaos will bring a new, yet liveable,
stage of stability to global and regional climate.
• [email protected]
Your Comments on some places to look for
chaos in climate changes?
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1. hydrologic cycle
2. flow of the Gulf Stream
3. release of trapped methane
4. ecosystem changes
5. human systems changes
• [email protected]
Your comments on more places to look for
chaos in climate changes?
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6. the global carbon cycle
7. clouds
8. aerosols
9. ocean wind patterns and currents
10. rapid polar glacier melting
11. changes in albedo
• [email protected]