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Transcript
Abrupt Climate Change
Tipping Elements in the
Earth’s Climate System
-Lenton et al. (2008)
Abrupt Tropical Climate
Change: Past and Present
-Thompson et al. (2006)
Seth T. Warthen
Graduate Student – ASP
The Ohio State University
Geography 5921
Overview / Outline
• Meet the Authors
• Review the Lenton et al. (2008) paper
• Review the Thompson et al. (2006) paper
• Overall conclusions
The Faces Behind the Science
Dr. Tim Lenton
• Prof. at University of
Exeter
• BA from U. Cambridge
• PhD from U. of East
Anglia
Dr. Lonnie Thompson
• Prof. at the Ohio State
University (BPRC)
• BS from Marshall University
• MS and PhD from OSU
• CV has two pages of awards
(65 pages total)
What’s actually “abrupt”?
• Lenton et al. (2008):
—“when the climate system is
forced to cross some
threshold, triggering a
transition to a new state at
a rate determined by the
climate system itself and
faster than the cause”
• Societal or ecological
definition:
—“A climatic change that
takes place so rapidly and
unexpectedly that human
and natural systems have
difficulty adapting to it”
What’s this “tipping point” you mentioned?
• Tipping Point:
– The critical point at which
the climate system is
altered
• Tipping Element:
– The portion of the
climate system that when
altered can push beyond
the tipping point
The canoe analogy
• Tipping Element:
– The portion of the
climate system that when
altered can push beyond
the tipping point
The canoe analogy
• Tipping Point:
– The critical point at which
the climate system is
altered
The canoe analogy
• The result:
– No easy way back
– Fun for the whole family!
Policy-relevant tipping elements
• Tipping elements
relevant to this
century
—Decisions relating to
element must be
within a “political
time horizon”
—Time to observe
change plus time to
trigger it lie within
“ethical time
horizon”
—A significant amount
of people care about
the fate of the
element
Ranking the threat
• High sensitivity / smallest
uncertainty:
– Greenland Ice Sheet, Arctic sea-ice
• Intermediate sensitivity / largest
uncertainty:
– West Antarctic Ice Sheet, boreal
forests, Amazon rainforest, ENSO,
West African monsoon
• Low sensitivity / intermediate
uncertainty
– Thermohaline Circulation
An early warning
• Anticipating the
bifurcation (tipping
point):
– Uses “degenerate
fingerprinting”
› Reconstruct t (tau)
characteristic of threshold
through time series
analysis
› Use in intermediate
complexity model
Lenton et al. (2008) Conclusions
• Tipping Points:
– Further work may make it possible to
create “early warnings” for some
tipping points
• Tipping Elements:
– There are numerous tipping elements
(WAIS, GIS, THC, ENSO, etc.) that have
various (and dire) impacts on climate
› Varying time scales and “abruptness”
› Some well within IPCC projected
warming for this century
– Climate is very complex… likely more
tipping elements yet to be discovered
Thompson et al.
(2006)
Abrupt tropical climate
change
Thompson et al. background
• Tropical / Low-latitude Glaciers:
– Used δ18O from glacial ice cores as
a proxy to examine temperature
fluctuations in the tropics
– Used 14C dating or organic material
• Goal:
‒ Figure out if parallels between the
current climate and glacial retreat
exist with those of the past
‒ Are the dynamics of tropical
glaciers changing?
Unprecedented glacial retreat
The last 400 years (in 5-yr averages)
• Accumulation (An):
– Only Quelccaya usable in Peruvian Andes
› Other sites had rapidly thinning layers
– Dasuopu has record somewhat inverse to others
› Is located in Himalayas (monsoon-dominated) where the others
are located on Tibetan Plateau (westerlies-dominated)
• Temperature (δ18O ):
‒ Low-latitude sites show similarities, but:
› Warming starts earlier in Tibetan Plateau
› Huascaran shows earliest Andean warming (closest to equator),
Sajama shows little trend (furthest south, very dry)
• Composites
‒ Show δ18O depletion (cooling) through Little Ice age, δ18O
enrichment (warming) in current warp period
‒ Greatest δ18O depletion 1810-1820
› Unknown volcanic eruption in 1809, Tambora eruption in 1815
The last 2000 years
(decadal Averages)
• Mostly Good agreement in
Climatic period timings:
‒ MWP (~900-1300 A.D.)
‒ LIA (~1400-1800 A.D.)
‒ CWP (~1850 A.D. -present)
– MWP and LIA not really seen in
Tibetan Plateau composite, but
all show anomalous δ18O
enrichment in recent centuries
› Signifies change in dynamics of
high altitude tropical glaciers,
regardless of if δ18O correlated
with temp or precip
› Spatially homogeneous nature
of temperature gradient
(compared to other
atmospheric variables) suggest
it’s the primarily responsible for
glacial retreat
Don’t get caught with your plants
down…
In case we needed more
evidence…
• Glacial retreat reveals hidden secrets:
‒ Distichia muscoides (plant) recovered from
Quelccaya was 14C dated to around 5100 y. old
› Implies temperatures in this region haven’t been
this warm since early Holocene
› Level of glacial retreat is unprecedented for last
5000 years
‒ Preserved Tyrolean “Ice Man” recovered from
Alps, 14C dated to 5050-5350 years old
• 5k Event - An abrupt cold snap indicated by:
‒ Recovery and carbon dating of previously frozen
specimens
‒ Marine records indicate spike in terrigenous
material
‒ Other fossil, artifact, and proxy evidence
Thompson et al. (2006) Conclusions
• Tropical glacial retreat:
– Recent accelerating retreat of glaciers
unprecedented for at least previous 25 millennia
– Retreat likely linked with the current
warm period
– Anthropogenic forcing has interrupted
the cooling of the late Holocene,
pushing us to a climate closer to that
of 5000 years ago
– “May signal that the climate system
has exceeded a critical threshold, and
that most low-latitude, high-altitude
glaciers are likely to disappear in the
near future”
Overall Conclusions
• The Climate can, has, and will change:
– Abrupt changes in climate aren’t overly
uncommon on a geologic timescale
› Dansgaard-Oeschger events, 5k event,
volcanic eruptions, etc.
– Glaciers are retreating on a level unseen
for 5000 years
– There exist tipping points and tipping
elements
› Glaciers may be an example of a tipping
element reaching a tipping point
› We may be able to predict these tipping
points
– Climate is very complex
Further Work?
• The rise of the model:
– Increased computing power leads to
more powerful climate models
– More paleoproxies:
– The more proxies we have to examine the
climate of the past, the more we can
understand about the current/future
– More analogues!
– Geoengineering:
– Definitely not a “best case” scenario, but
the way things are progressing now…
References / Questions?
“Ice asks no questions,
presents no arguments,
reads no newspapers
listens to no debates.
It is not burdened by ideology
and carries no political baggage as
it changes from solid to liquid.
It just melts.”
-From A World Without Ice by
Henry Pollack, 2009
Alley R. B. and Coauthors, 2003: Abrupt Climate Change. Science, 299, 2005-2010,
doi:10.1126/science.1081056.
Lenton T. M., H. Held, E. Kriegler, J. W. Hall, W. Lucht, S. Rahmstorf, and H. J. Schellnhuber,
2008: Tipping elements in the Earth’s climate system. Proc. Natl. Acad. Sci., 105, 17861793, doi:10.1073/pnas.0705414105.
Lenton T. M.: Early warning of climate tipping points. Nature Climate Change, 1, 201-209,
doi:10.1038/NCLIMATE1143
Thompson L. G. and Coauthors, 2006: Abrupt tropical climate change: Past and present. Proc.
Natl. Acad. Sci., 103, 10536-10543, doi:10.1073/pnas.0603900103.