Cambiamenti Climatici

Transcript

Climate of the last 100 My or more
2009 GEOLOGIC TIME SCALE
MESOZOIC
lunedì 12 marzo 2012
20
5E C5E
6 C6
11.6
SERRAVALLIAN
M
16.0
E
20.4
23.0
10 C10
30
11
12
13
35
C11
C12
C13
OLIGOCENE
C9
L
E
L
23
150
C21
C22
C23
M
E
180
190
LUTETIAN
48.6
24
C25
26
C26
60
27
28
65
29
C27
C28
C29
30 C30
PALEOCENE
55
55.8
L
THANETIAN
58.7
M
230
SELANDIAN
61.7
E
220
240
DANIAN
65.5
250
83.5
85.8
89.3
280
93.5
99.6
300
320
APTIAN
EARLY
125
BARREMIAN
VALANGINIAN
BERRIASIAN
TITHONIAN
M22
LATE
KIMMERIDGIAN
OXFORDIAN
MIDDLE
CALLOVIAN
BATHONIAN
BAJOCIAN
AALENIAN
340
130
136
140
360
380
156
161
165
400
420
183
EARLY
SINEMURIAN
HETTANGIAN
190
440
197
201.6
460
204
480
LATE
NORIAN
500
228
CARNIAN
MIDDLE
LADINIAN
ANISIAN
EARLY
OLENEKIAN
INDUAN
235
520
241
245
250
251.0
WORDIAN
ROADIAN
KUNGURIAN
E
PENNSYLVANIAN
SAKMARIAN
ASSELIAN
GZELIAN
KASIMOVIAN
MOSCOVIAN
BASHKIRIAN
SERPUKHOVIAN
MISSISSIPPIAN
EON
ERA
251
254
PERIOD
260
266
268
271
276
284
297
299.0
304
306
312
TOURNAISIAN
L
GIVETIAN
EIFELIAN
EMSIAN
PRAGHIAN
540
L
M
E
PRIDOLIAN
LUDFORDIAN
GORSTIAN
HOMERIAN
SHEINWOODIAN
TELYCHIAN
AERONIAN
RHUDDANIAN
HIRNANTIAN
L
KATIAN
SANDBIAN
M
DARRIWILIAN
DAPINGIAN
FLOIAN
E
Furongian
Series 3
Series 2
Terreneuvian
TREMADOCIAN
STAGE 10
STAGE 9
PAIBIAN
GUZHANGIAN
DRUMIAN
STAGE 5
STAGE 4
STAGE 3
STAGE 2
FORTUNIAN
398
407
411
416
419
421
423
426
428
436
439
444
446
1250
1500
1750
1000
1200
MESOPROTEROZOIC
488
492
496
501
503
507
510
517
521
535
542
ECTASIAN
1400
CALYMMIAN
1600
STATHERIAN
1800
OROSIRIAN
PALEOPROTEROZOIC
2050
RHYACIAN
2250
2300
SIDERIAN
2500
2500
NEOARCHEAN
2750
2800
3000
468
472
479
850
STENIAN
2000
455
461
CRYOGENIAN
1000
385
392
542
TONIAN
345
374
NEOPROTEROZOIC
750
318
326
BDY.
AGES
(Ma)
630
FAMENNIAN
FRASNIAN
M
EDIACARAN
VISEAN
LOCKHOVIAN
TOARCIAN
PLIENSBACHIAN
CAPITANIAN
ARTINSKIAN
E
168
172
176
M
CHANGHSINGIAN
WUCHIAPINGIAN
359
145.5
151
PERMIAN
L
260
112
RHAETIAN
210
YPRESIAN
70.6
ALBIAN
200
C24
25
TURONIAN
CENOMANIAN
M12
M14
M16
M18
M20
M29
170
SANTONIAN
CONIACIAN
HAUTERIVIAN
160
PRIABONIAN
40.4
EOCENE
C20
M0r
M1
M3
M5
M25
37.2
PALEOGENE
22
130
BARTONIAN
45
21
120
140
RUPELIAN
C17
19 C19
50
CHATTIAN
C18
20
110
28.4
18
40
34 C34
LATE
AGE
(Ma)
65.5
CAMPANIAN
M10
33.9
15 C15
16 C16
17
100
AQUITANIAN
6B C6B
9
13.8
LANGHIAN
6C C6C
7 C7
7A C7A
8 C8
90
BURDIGALIAN
6A C6A
25
C33
80
PICKS
(Ma)
PROTEROZOIC
5C C5C
5D C5D
32 C32
33
7.2
TORTONIAN
MAASTRICHTIAN
AGE
PRECAMBRIAN
3250
3500
ARCHEAN
5B C5B
30 C30
31 C31
AGE
PERIOD EPOCH
(Ma)
CARBONIFEROUS
C5A
L
5.3
70
PICKS
(Ma)
DEVONIAN
15
C5
0.01
1.8
2.6
3.6
AGE
PALEOZOIC
ORDOVICIAN SILURIAN
5A
C4A
MIOCENE
5
C4
NEOGENE
4A
10
ZANCLEAN
MESSINIAN
3A C3A
4
GELASIAN
PIACENZIAN
CRETACEOUS
PLIOCENE
C3
TERTIARY
Cambiamenti Climatici - Basi scientifiche
5
3
CALABRIAN
PERIOD EPOCH
JURASSIC
2A C2A
HOLOCENE
AGE
(Ma)
CHRON.
PLEISTOCENE
PICKS
(Ma)
HIST.
QUATERNARY
AGE
TRIASSIC
C1
C2
EPOCH
RAPID POLARITY CHANGES
1
2
PERIOD
ANOM.
CHRON.
HIST.
ANOM.
AGE
(Ma)
MAGNETIC
POLARITY
CAMBRIAN*
CENOZOIC
MAGNETIC
POLARITY
MESOARCHEAN
3200
PALEOARCHEAN
3600
3750
EOARCHEAN
3850
HADEAN
*International ages have not been fully established. These are current names as reported by the International Commission on Stratigraphy.
Walker, J.D., and Geissman, J.W., compilers, 2009, Geologic Time Scale: Geological Society of America, doi: 10.1130/2009.CTS004R2C. ©2009 The Geological Society of America.
Sources for nomenclature and ages are primarily from Gradstein, F., Ogg, J., Smith, A., et al., 2004, A Geologic Time Scale 2004: Cambridge University Press, 589 p. Modifications to
the Triassic after: Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for
the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi: 10.1130/G22967A.1; and Kent, D.V., and Olsen, P.E.,
2008, Early Jurassic magnetostratigraphy and paleolatitudes from the Hartford continental rift basin (eastern North America): Testing for polarity bias and abrupt polar wander in
association with the central Atlantic magmatic province: Journal of Geophysical Research, v. 113, B06105, doi: 10.1029/2007JB005407.
Infact the energetic
ditribution and velocity of
circulation systems are
related to the geography
and oceans-continents
configuration.
Changes on the
circulation systems will
produce changes in the
energy distribution, that
is strongly related to the
climat.
Plate tectonics change the
oceans-atmosphere-continents relationships
Bärbel Hönisch, et al. Science 335, 1058 (2012)
Climate of the last 60 My
Hominids of the last 10 My
This figure shows the climate record of Lisiecki and Raymo (2005) constructed by combining
measurements from 57 globally distributed deep sea sediment cores. The measured quantity is
oxygen isotope fractionation ([[δ18O]]) in benthic foraminifera, which serves as a proxy for the
total global mass of glacial ice sheets.
Lisiecki and Raymo constructed this record by first applying a computer aided process of
adjusting individual "wiggles" in each sediment core to have the same alignment (i.e. wiggle
matching). Then the resulting stacked record is orbitally tuned by adjusting the positions of peaks
and valleys to fall at times consistent with an orbitally driven ice model (see Milankovitch cycles).
Both sets of these adjustments are constrained to be within known uncertainties on
sedimentation rates and consistent with independently dated tie points (if any). Constructions of
this kind are common. However, they assume that ice volume is driven by changes in insolation,
and such data therefore cannot be used to establish the existence of such a relationship.
Climate of the last 800 Ky or more
CO2 and CH4
concentrations
follow temperature
(more on this in
later lectures)
Temperature cycles
of 8-10°C
Glacials and
interglacials
Slow (~ few kyear)
transitions
Sea level change 100 My
Sea level of last 900 ky
Sea level records back up
other climate proxies
At glacial maximum, sea
level was about 130 m
below current
Climate of the last 250 ky
Comparison of various global and Arctic
proxy records spanning the past 250,000
years.
Approximate durations of interglacial MIS are
indicated by yellow bars.
(A) June insolation values in W/m2 for 65°N.
(B) Greenland ice core (North Greenland Ice
Core Project) δ18O values expressed as ‰ in
relation to Vienna standard mean ocean water.
(C) Global stacked benthic δ18O values.
(D) The red dashed line indicate the number of
planktic foraminifera per gram of sediment in
the GreenICE core.
(E) Ice-rafted debris from the GreenICE core off
the coast of Greenland/Ellesmere Island
measured as the weight percentage of the
sediment fraction >63 μm.
(F) the black line indicates relative % herb
pollen (Lake E). (G)
gray lines indicate relative % tree and shrub
pollen.
(H) Total organic carbon.
(I) Magnetic susceptibility as a proxy for
seasonal lake ice cover.
Brigham-Grette J PNAS 2009;106:18431-18432
Climate frequencies last 2 My
• Power spectra from
ocean sediment cores
• Peaks correspond to
Earthʼs orbital variations
Orbital Theory
Serbian mathematician Milutin Milankovitch proposed in 1920
that variations in Earthʼs orbit would influence climate
Orbital Theory
Eccentricity
96-100 kyr period
Obliquity
41kyr period
Precession
19-21kyr period
Orbital Theory
Distance from the Earth to the sun is different at
opposite sides of the orbit (i.e. 6 months apart)
Eccentricity changes cyclically with a period of
about 96,000 years.
Eccentricity varies between about 0 and 0.07
(the orbit stretched by 7% away from a circle)
Earth receives the same total radiation from the
sun regardless of eccentricity, but the amount
received can be different for the two
hemispheres
Circular orbit: annual radiation received by each
hemisphere is the same
Eccentricity = 0.07: difference in solar radiation
up to 28% between the two hemispheres
Currently: eccentricity is 0.0174: Southern
hemisphere receives 6.7% more radiation in a
year
Orbital Theory
• Earth's axis of rotation is tilted
relative to the orbital plane
• Currently the tilt (obliquity) is
23.5°
• Tilt varies between about 21.5°
and 24.5° with a period of about
41,000 years
• Large obliquity: seasons more
exaggerated
• Change in the strength of the
seasons can affect the entire
climate system
Orbital Theory
• The Pole Star (Polaris) is currently 44 minutes of arc (three-quarters of
one degree) away from the Earth's axis. Taking a time-lapse
photograph of the northern night sky will reveal all the stars rotating
around Polaris, regardless of the time of year.
• Because of the 41,000 year wobble in the angle of obliquity, there has
not always been a Pole Star. Ancient Greek texts from Hipparchus (125
BC) state 'at the Pole there is no star at all!'.
• Shakespeare was wrong when he said in 1599 that Julius Caesar is 'as
constant as the Northern Star'. There was no Northern Star.
• Why does the obliquity vary only by a very small amount? If the
obliquity were 90o then the North Pole could point at the sun throughout
a whole year while the South Pole would be in perpetual darkness. This
doesn't happen because of the influence of the moon on the Earth's
orbit. Without a moon the Earth's obliquity would wobble chaotically,
leading to dramatic variations in climate. Perhaps without our moon no
life would ever have evolved on Earth.
• The direction of the long axis
of the ellipse rotates slowly
• Influences which hemisphere
has its summer when Earth is
closest to the Sun
• The period of precession of
the Earth's orbit is
complicated by other planets
(mainly Jupiter); it is between
Radiatiation effect
Sola radiation and orbital variations
Calculated annual
mean solar radiation
received by NH mid
latitudes (65°N) by
including all orbital
variations
Other cyclicities?
• Evidence for large amplitude
ʻcyclesʼ (DansgaardOeschger) with periods
less than 10 kyears
• Some evidence that T
increased before expected
by orbital changes
Greenland ice core record
of oxygen isotope ratio
Power spectrum for
Greenland ice core with
dominant periods (in
years) marked at the top
Climate fluctuations during Glacials
• Heinrich iceberg events
– Peaks of ice-rafted debris
in marine sediments (7-10
kyear timescale)
• Dansgaard-Oeschger ʻcyclesʼ
– Peaks in the Oxygen
isotope from Greenland
cores
Bipolar seesaw
Bipolar seesaw - last transition
• De-glaciation period halted
by 2000 year glacial period
(Younger Dryas)
• Antarctic cold reversal
preceded Younger Dryas by
>1000 years
• Present interglacial much
more stable than glacial
period
• Evidence for significant,
rapid regional climate
fluctuations in present
interglacial (much current
research on this critical
issue)
Climate of the last 11 ky - Holocene
• The Holocene is more relevant to our current climate than the glacial period
• An abrupt event in the early Holocene (8.2 kyear BP)
– European annual mean T dropped 2°C
– Significant decrease in N. Atlantic SST
– Possibly world-wide (New Zealand glaciers)
• Further events documented
from pollen and lake level
records in Europe, N America,
Australia
Summary
• The magnitude of the Northern Hemisphere warming over the 20th century is
likely to have been the largest of any century in the last 1000 years
• Warming of last 3 decades has been globally synchronous
– But the record is limited earlier than 1000 years BP
• The last 1000 years are dominated by the Little Ice Age and the Medieval Warm
Period
– These were likely not globally synchronous phenomena
– Controversy about the magnitude and causes of these events
• Large and rapid non globally synchronous decadal temperature changes
occurred during the last Ice Age (10-100 kyears BP)
– Particularly in NH regions
– 5-10°C changes per decade locally
• Less pronounced, almost globally synchronous temperature changes also
occurred
• Evidence for significant, rapid regional temperature changes in the present 10
kyear interglacial (Holocene)
– No evidence for globally synchronous events
Is the recent warming unusual?
• Our current understanding of past climates suggests that the
current warming, particularly in the last 30 years, is
distinguished by being globally synchronous
• Although current global mean temperatures are likely the
highest of the last 1000 years, there is no evidence that this is
unusual, considering the gaps in our understanding of what
controls climate fluctuations (the early Holocene was warmer
than at present)
• The rate of change of temperature is lower now than in some
deglaciation periods. Further natural or human-induced abrupt
regional climate changes cannot be ruled out.
• There is much to learn about natural climate variability

Cambiamenti Climatici

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