Paleoclimate and Sea Level
Changes
Global climate changes
• Glaciers and permafrost
• Desertification
• Evidence for change
– Long and short time scales
Graphical Representation of
Climate in Geologic Time
Earth History
Precambrian ???? – 540 Mio a
Paleozoic 540 – 250 Mio a
Mesozoic 250 – 65 Mio a
Proxies
Cenozoic
Tertiary 65 – 1.8 Mio a
Quaternary 1.8 Mio a - today
Measurements
Permian
Major Glaciation
Underwent cycles of
glaciations
ice sheets existed
at lower latitudes
292 - 250 Ma
Antarctic
ice sheets
formed
34 Ma
610 – 575 Ma
Holocene – cycle of
glaciation and
melting of ice caps
– rising sea levels
1.8 Ma –
10 Kya
438 – 408 Ma
Paleozoic Era
Interglacial period
plants invade
land
Billions of years ago
Major continental shifts
– earth extremely hot
1 Ma
Pleistocene
Ice Age
55 – 52 Ma
Paleocene
Elevated greenhouse
gases warmed up
planet
Palm trees in Alaska
Crocodiles in the
Arctic
18 Kya
Last glacial
period
Precambrian
beginning – 540 Mio a
Evidence of two major glaciations
„Faint Sun Paradox“
„Snowball Earth“
Paleozoic: Cambrian
N hemisphere (north of 30°) ocean
Increased tectonic activity
CO2 high, up to 10x of today
Warm and wet globally
Paleozoic:
Ord: Ice formations 490 – 440 Mio a
Sil Dev: no glaciation 440 – 350 Mio a
Car Per: Ice ages 350 – 250 Mio a
Reason for this variation?
Carboniferous Ice age settings:
Carboniferous Ice age settings:
Continent near south pole
Maritime influence
Subfreezing T during most of year
Marine transgression – continental
flooding
Reduced seasonality
Carboniferous Ice age settings:
Reason for
this variation?
CC driven by land – sea distribution
CC driven by tectonics
Mesozoic Climate Variability:
Trias 250 – 205 Mio a: Pangaea
Jurassic 205 – 145 Mio a:
Pangaea break up
Cretaceous 145 – 65 Mio a: Continents as
we know them today
Generally warm and arid period
No evidence of glaciation
Why?
Mesozoic Climate Variability:
Trias
250 – 205 Mio a:
Pangaea
Pangaea characteristics:
Large land mass at equator
Lower sea levels
Reduced rate of tectonics
Extreme continental climate
Extreme dry
Pangaea break - up:
Tethys seaway / transglobal equatorial
seaway formed
Heating of water at
equator
Heat transport to
low latitudes
Mesozoic Climate Variability:
Pangaea: No continent in pole position
Pangaea – too dry
Transequatorial seaway –
heat redistribution
However – Model problem
Cenozoic Climate Variability:
Tertiary (65 – 2 Mio a)
Quaternary (2 Mio a – today)
Relatively warm in early Cenozoic
Early Eocene (55-50 Mio a) tropical
conditions 10 – 15° further polewards
Cenozoic Climate Deterioration:
Oligocene: 25 Mio a
Initiation of Antarctic
Ice Shield
Miocene: 15 – 10 Mio a
Growth of Antarctic
Ice shield
Cenozoic Climate Deterioration:
Hypothesis 1:
1) Transequatorial waterway blocked
2) Transpolar waterway opened through
Drake Passage – reduced heat transfer
3) Growth of ice – increase in albedo
4) Cooling
Cenozoic Climate Deterioration:
Cenozoic Climate Deterioration:
Hypothesis 2:
1) Change in continental topography
2) Colorado / Tibetian Plateau uplift
3) Winter cooling of N-hemisphere
4) Ice formation
Cenozoic Climate Deterioration:
Hypothesis 3:
1) Orogenic uplift (as in Hyp 2)
2) Alpine / Himalayas (20-30 Mio a ago)
3) Increase in silicate weathering
4) Removes CO2 from atmosphere
Cenozoic Climate Deterioration:
Hypothesis 3:
5) Silicate + CO2 = Bicarbonate
6) Bicarbonate is soluble
7) Transport to oceans and deposition
Indirect effect by reduced greenhouse
forcing
Cenozoic Climate Deterioration:
Summary: Combination of processes is
necessary. Land – sea distribution,
ocean heat transfer, orography change
and CO2 are all likely to cause cooling
of earth.
Right now, since 10 Mio a we are in an
Ice age (both poles ice capped) with
glacial and interglacial periods
Quaternary period:
Pleistocene 1.8 Mio a – 10Ta
Changes in former examples in Mio a
Drivers needed with
cyclicity of 10-100Ta
e.g. Earth orbit
variations around
sun
Quaternary period:
2 model approaches for
glacial / interglacial
A) Ice volume changes are driven by
orbital forcing. Linear responses at
23/41 Ta, non-linear at 100 Ta.
B) Ice volume changes happen, quasi
period fluctuations which then are
modulated by orbital forcing
Quaternary period:
Important: Orbital forcing alone is not
enough. Orbital forcing must interact
with internal climate variations
Quaternary period:
C02 feedbacks: C-cycle impacts on
matching time-scales
e.g. Oceans: millenium time scale
However, existing ice core records do
not allow resolution of the phase
relationship between CO2 and T
Cause – effect still unclear
Quaternary period:
Pleistocene – Holocene boundary
10-11 Ta
Glacial maximum at 18 Ta
Holocene thermal maximum at 6 Ta
Rapid climate changes
• When were the Ice Ages?
– Periodicity
• Extent of glaciation
• Climate characteristics
• Possible forcing for climate change
– Astronomical
– Tectonic
– Climate dynamics
History of Ice Ages
• Indications from geologic record
– First glaciation occurred in the Pre-Cambrian Era
– Periods of glaciation occur about every 200 million
years
• Pleistocene ice ages are the most well known
– Height of Ice Age between 150,000 and 10,000 years
BP
– Although, episodes of advance/retreat have occurred
every 100,000 years since 900,000 years BP
Closer Look at
Pleistocene Glaciation
• Several periods of warm interglacials and
cold glacials
– 130 ky BP – Emian interglacial
• Climate similar to what we have today
• However, very unstable (Will we see this?)
– 110 ky BP – Rapid cooling, leading to glacial
advances
• Much drier climate due to increase in continental
ice at expense of marine ice and moisture
Pleistocene Glaciation (cont…)
– 60 ky BP – large amplitude oscillations
between warm and cold
– 30 ky BP – More rapid cooling ends with Last
Glacial Maximum (18 ky BP)
• Very arid climate globally
• Expansive desertification and reduction in forest
land
– Interstadials – frequent and brief warm
periods
– Heinrich events – very cold periods
Extent of Last
Glacial Maximum
Transition to the Holocene
– 14 ky BP – Major climate swings ending with the
Younger Dryas (Glacial surge)
• Forests begin to rebound and ice begins to recede
– 10 ky BP – warming and beginning of the Holocene
Epoch
• Rapid warming (actually warmer, wetter than today)
– Especially Sahara (very little desertification)
• 1500-year oscillation of warm-cold cycles, outburst floods
(stochastic resonance?)
• Lesson learned – LARGE CLIMATE SWINGS
ARE NORMAL!!!!
Theories for the
Onset of Glaciation
• Astronomical
– Milankovitch cycles
– Changes in solar parameter
• Tectonic
– Continental drift
– Orogenesis
• Climate dynamics
– Increased planetary albedo
– Interruption of Gulf Stream by termination of sinking of
hypersaline water in North Atlantic
– Water vapor fluxes
Milankovitch Cycles
• Eccentricity – changes in shape of earth’s
revolution about the sun (100 ky cycle)
– Significant effect on insolation
• Obliquity – changes in axial tilt (41 ky
cycle)
– Most significant effect on albedo
• Precessionary – reversal of equinoxes (19
and 23 ky)
Changes in Insolation
Implications of
Milankovitch Cycles
• High correlation with solar and climate
cycles
• Work of Saltzman and other show large
oscillations in climate every 100 ky
(Eccentricity)
• Climate oscillations to lesser extent on
20 ky (Precession) and 40 ky (Obliquity)
cycles
Causes of glaciation/climate
change
• Atmospheric gases and dust
– Greenhouse gases->warming
– Dust (volcanoes)->cooling
• Positions of the continents
– Ice sheet nucleation with continents in polar
positions
– Changes in ocean circulation
• Orbital factors
Milankovich cycles are
cycles in the Earth's orbit
that influence the amount
of solar radiation striking
different parts of the Earth
at different times of year.
They are named after a
Serbian mathematician,
Milutin Milankovitch, who
explained how these
orbital cycles cause the
advance and retreat of the
polar ice caps.
http://deschutes.gso.uri.edu/~r
utherfo/milankovitch.html
The phase difference between two
paleoclimatic time series is used to
interpret processes that link
Milankovitch-cycle-driven
insolation changes with Earth's
climate.
What is phase?
The figure shows three examples of
the phase between two time series. In
the top figure, two time series have
different amplitudes but are exactly
in phase (Phase=0). In the middle
diagram, two time series are exactly
out of phase (Phase=180). The
bottom diagram shows the general
case where one time series leads or
lags a second time series. The
magnitude of the lead or lag is the
phase angle and can be positive or
negative.
http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html
The influence of these cycles on insolation (INcident SOLar radiATION) at different
latitudes is shown for 65 degrees north latitude from the present to 1 million years ago.
In the Northern Hemisphere, peak summer insolation occurred about 9,000 years ago
when the last of the large ice sheets melted. Since that time Northern Hemisphere
summers have seen less solar radiation.
http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html
Annual energy flow to earth from sun
The Greenhouse effect
Greenhouse gases such as
CO2 absorb energy and stop
it from radiating away
(Keller, 2002)
Concentration
of
Atmospheric
CO2 over time
(Keller, 2002)
Global temperature changes
Maximum extent of glacial ice sheets during the Pleistocene
glaciation (Keller, 2002)
Global temperature changes
Arid lands and desertification
National Geographic map of the world
Terrestrial Ecosystems are an…
•
•
•
Integral part of global carbon system
Plants take in and store carbon dioxide from the atmosphere through photosynthesis
Below ground microbes decompose organic matter and release organic carbon back into the
atmosphere
www.bom.gov.au/.../ change/gallery/9.shtml
Cycle shows how nature’s sources of CO2 are self regulating – that which is released will
be used again – Anthropogenic carbon not part of natures cycle – is in excess