Transcript Younger Dryas

Climate change prior to 1900
The ice core record indicates that greenhouse gases co-varied with antarctic
temperature over glacial-interglacial cycles, suggesting a close link between
natural atmospheric greenhouse gas variations and temperature.
Variations in CO2 over the last 420 kyr broadly followed antarctic temperature,
typically by several centuries to a millennium (Mudelsee, 2001).
The sequence of climatic forcings and responses during deglaciations
(transitions from full glacial conditions to warm interglacials) are
well documented. High-resolution ice core records of temperature
proxies and CO2 during deglaciation indicates that antarctic
temperature starts to rise several hundred years before CO2
(Monnin et al., 2001; Caillon et al., 2003).
During the last deglaciation, and likely also the three previous ones,
the onset of warming at both high southern and northern latitudes
preceded by several thousand years the first signals of significant sea
level increase resulting from the melting of the northern ice sheets
linked with the rapid warming at high northern latitudes (Petit et al.,
1999; Shackleton, 2000; Pépin et al., 2001).
IPCC, 4th Report, 2007
(A) The ice-equivalent eustatic sea level history over
the last glacial-interglacial cycle according to the
analysis of Waelbroeck et al. (2002). The smooth black
line defines the mid-point of their estimates for each
age and the surrounding hatched region provides an
estimate of error. The red line is the prediction of the
ICE-5G(VM2)
IPCC, 4th Report, 2007
(B) The fit of the ICE-5G(VM2)
model prediction (red line)
to the extended coral-based
record of RSL history from the
island of Barbados in the
Caribbean Sea (Fairbanks, 1989;
Peltier and Fairbanks, 2006)
over the age range from 32 ka to
present. The actual iceequivalent eustatic sea level
curve for this model is
shown as the stepdiscontinuous brown line.
The individual coral-based
estimates of RSL (blue) have
an attached error bar that
depends upon the coral species.
The data denoted by the coloured
crosses are from the iceequivalent eustatic sea level
reconstruction of Lambeck and
Chappell (2001) for Barbados
(cyan),Tahiti (grey), Huon
(black), Bonaparte Gulf
(orange) and Sunda Shelf
(magenta).
Younger Dryas
Towards the end of the last Ice
Age, climate warmed, then
suddenly cooled again for
almost 1000 yrs
Younger Dryas
The Younger Dryas
The Younger Dryas saw a rapid return to glacial conditions in the higher
latitudes of the Northern Hemisphere between 12,900 – 11,500 years
before present (BP) in sharp contrast to the warming of the preceding
interstadial deglaciation. The transitions each occurred over a period of
a decade or so.Thermally fractionated nitrogen and argon isotope data
from Greenland ice core GISP2 indicates that the summit of Greenland
was ~15 °C colder than today during the Younger Dryas. In the UK,
coleopteran (fossil beetle) evidence suggests mean annual temperature
dropped to approximately -5 °C, and periglacial conditions prevailed in
lowland areas, while icefields and glaciers formed in upland areas.
Nothing of the size, extent, or rapidity of this period of abrupt climate
change has been experienced since.
Possible Cause for the Younger Dryas
North Atlantic deep water formation – cut off by the cap of relatively light
freshwater
Figure 15-2
Cameron Lee C. , The Younger Dryas Period
Cameron Lee C. , The Younger Dryas Period
Cameron Lee C. , The Younger Dryas Period
Cameron Lee C. , The Younger Dryas Period
Cameron Lee C. , The Younger Dryas Period
Cameron Lee C. , The Younger Dryas Period
The Atlantic Conveyor
Did the Younger Dryas was
caused by the shutdown of the
Atlantic Conveyor?
• As the Laurentide ice
sheet retreated, melt
water was diverted
from the Mississippi
River to the St.
Lawrence River
• North Atlantic ocean
became capped with
freshwater  not
dense enough to sink
 thermohaline
circulation shut down
for ~1000 yrs
Replacing salty oceans with
fresh water could trigger a
Positive Feedback Loop:
• No salty water than no
downwelling
• No downwelling than less
warm water reaching northern
part of North Atlantic
• Less warm water than cooler air
• Cooler air than colder temperatures
• Colder than more intense sea ice growth
• More sea ice growth than glacier advance
• More ice than higher albedo
• Higher albedo than less heat in climate system and thus
reinforces colder temperatures and sustains colder climate
http://www.falw.vu/~renh/YD-worldmap.JPG
Changes at the and of Last Ice Age
Northern Europe
North America
17 000
Glaciers retreat in Alps
Major collapse of part of ice
sheets
16 000
Wet period over US with lake
levels showing highest levels
around 15 000 BP
15 000
abrupt warming (~14 900 BP)
with forest expansion, known
as Bölling interstadial
14 000
Return to colder conditions,
around 14 000 BP for about
500 years, known as Older
Dryas.
Warming around 13 500 BP,
although colder than in
Bölling, known as Allerød
interstadial.
Cordilleran ice sheet retreat
Burroughs, Climate Change, 2001
TIME
BP
Northern Europe
North America
13 000
Around 12 900 BP a sudden
Drainage of meltwater from
and dramatic cooling, known as Laurentide ice sheet switches
Younger Dryas
from Gulf of Mexico to St
Lawrence.
Surges of iceberges out of
Hudson Bay cooled the North
Atlantic, probably triggering the
Younger Dryas
12 000
Around 11 600 BP sharp and
sustained warming, its initial
stage is knows as Pre-Boreal
Readvance of Laurentide ice
sheet may redirected melting
water back to Gulf of Mexico
switching off the Younger Dryas
11 000
Spreading of forests across
northern Europe
Cordilleran ice sheet melts
rapidly and disappears at
around 10 000 BP
10 000
Forests established at high
Laurentide ice sheet declines
latitudes, but fennoscandian ice more slowly and finally melts at
sheet did not disappear until
around 7000 BP.
around 8500 BP.
Burroughs, Climate Change, 2001
TIME
BP
Changes during the Holocene
Period
Central England
Europe
Boreal
5500-6900 BC
Temperatures: JA: 16.3; DJF:
3.2, annual: 9.3
~1-2°C warmer than today
Atlantic
3000-5500 BC
Temperatures: JA: 17.8; DJF:
5.2, annual: 10.7
Wetter than today
Rapid peat build-up in N.
Europe, but cold spells in Alps
(5500-4500 BC)
Sub-boreal
1000-3000 BC
Temperatures: JA: 16.8; DJF: Generally dry and warm until
3.7, annual: 9.7
~1500 BC, much cooler and
wetter until ~1200 BC, than
warmer
Sub-atlantic
900 BC onwards
Temperatures: JA: 15.1; DJF:
4.7, annual: 9.3
(900 -450 BC)
(At present JA: 15.8; DJF:
4.2, annual: 9.4 )
Cooler, wetter 900-450 BC, than
warmer, drier until ~AD 400
than colder and more variable
until ~AD 1000
Changes during the Holocene
Period
Sahara
North America
Pre-boreal
6900-8300
Lake Chad 52 m higher
(area 400 000 km2)
Boreal
5500-6900 BC
Wetter in Egypt
Laurentide ice sheet expanded
(Cochrane readvance 4700-6500
BC)
Atlantic
3000-5500 BC
Lake Chad still 30-40 m
higher than present, moist
except 3500-3800 BC
Sharp cooling in White Mountains
3300-2800 BC
Sub-boreal
1000-3000 BC
Moist period ended ~2350
BC, thereafter much drier
Cooling in White Mountains
~1200 BC.
Northern Great Plains warmer (12°C) and drier until ~2000 BC
Sub-atlantic
900 BC onwards
Generally arid but some
evidence of more winter
rain in North Africa
Northern Great Plains drier than
now until AD 1200; with extreme
drought AD 200-370, 700-850,
1000-1200.
White Mountains coldest ~900 AD
Climate change in the human history
Medieval Warm Period and Little Ice Age
were the most evident climate fluctuations
during last millenium
Greenland Temp.
(°C)
-32.0
-31.0
Bermuda Rise SST
(°C)
21
22
23
24
West African SST
(°C, anomaly)
25
-6
-4
-2
0
2
0
500
a
Little Ice Age
b
Age
(yr BP)
1000
Medieval Warm Period
1500
2000
2500
Mid-Neoglacial
Medieval Warm Period - Medieval Climatic Optimum
Although there is no evidence of sudden change there are
some pointers to the fact that the climate of northern
Europe became more warmer during the ninth and tenth
centuries:
• Expansion of economic and agricultural activity to the
north,
• Grain was grown in the Norway further north than today,
• Crops were grown in Britain at higher levels than it is
economic today,
• Norse colonization of Iceland and Greenland.
Tree rings evidence shown than warmer period in northern
Fennoscandia lasted from 870 to 1100, but on Greenland
warmer period lasted from around 600 to the fourteenth
century.
Eric The Red was a Viking explorer. He was born in around 950 in
Norway. His father was banished from Norway because he killed a
man. In 982 Eric the Red was banished from Iceland for three
years because he also killed a man. He sailed to Greenland. After
three year he returned to Iceland and than led a group of colonists
to Greenland in 986.
His exploration to Greenland had 400 to 500 settlers in 14 ships
Farm under the Sand
(Western Settlement)
It happens in Greenland...that all that is taken there from other countries is
costly there, because the country lies so far from other countries that people
rarely travel there. Every item, with which they might help the country, they
must buy from other countries, both iron and all the timber with which they
build houses. People export these goods from there: goatskins, ox-hides,
sealskins and the rope...which they cut out of the fish called walrus and
which is called skin rope, and their tusks...
The people have been christened, and have both churches and priests....
(King's Mirror, 13th c Norway)
The mild climatic period was fairy
short lived , around ~ AD1200 the
ever-increasing cold was making
life extremely difficult, and after
some years no supply ships were
able to reach Greenland through
the ice-choked seas.
By about 1350, the settlements in
southwestern Greenland had been
abandoned.
In 1408 a wedding was performed
in the Hvalsey Church. It was not
only the last service at Hvalsey, but
also last written record of the
Vicking presence in the region.
Hvalsey Church,
Greenland
http://explorenorth.com/library/weekly/aa121799.htm
The Little Ice Age
• ~1450 to 1900 A.D.
• Regional (global?) expansion of mountain glaciers
• Cooling of a few tenths of a degree C
• NW Europe, Western U.S., S. America
• Best explanation is
– increased volcanism
– decrease in sun’s radiation output
• Maunder Minimum
The little ice age ~1600 to ~1850
A Frost Fair on the Thames
at Temple Stairs (1684)
Abraham Hondius, 1684
Extensive advance of glaciers in Europe
Long, severe winters
Was it global?
Recent Warming since 1850 AD
• Coincident with Industrial Revolution and
rapid and large increase in CO2
• Climate changes in Europe
• Climate changes in south-eastern Asia
• Climate changes in Balitc Sea Region
• El-Nino
Fourth Report of IPCC
IPCC SREX
Assessment of Climate Change for the Baltic Sea Basin
http://www.hzg.de/institute/coastal_research/projects/baltex/bacc_do
wnloads/index.html