Climate Changes: Past and Future - Universitetet i oslo · –Decrease in extreme cold and extreme...
Transcript of Climate Changes: Past and Future - Universitetet i oslo · –Decrease in extreme cold and extreme...
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Climate Changes:
Past and Future
Chapter 16 Lecture
Redina L. Herman
Western Illinois University
Understanding
Weather and
Climate
Seventh Edition
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Department of Geosciences www.ucalgary.ca
BLUE PLANET
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Department of Geosciences www.ucalgary.ca
WHITE PLANET
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Department of Geosciences www.ucalgary.ca
EMERALD PLANET
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Department of Geosciences
EMERALD PLANET
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History of the Biosphere
Fig 13
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200 000 yr BP
Homo sapiens evolve East Africa
70 000 yr BP
The Cognitive Revolution
13 000 yr BP
The Agricultural Revolution
12 000 yr BP
Homo sapiens only humans
200 yr BP
The Industrial Revolution
sapiens = wise (latin)
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Methods for Determining Past Climates
• Oceanic Deposits
– Scientists extract deep cores of
material that have been deposited
over long periods, with more recent
material constantly burying older
material.
– Cores include the bones and shells
of plankton and other animal life.
– The information contained in the
oxygen in the calcium carbonate is
most important for determining past
climates.
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• Ice Cores
– Scientists determine oxygen ratios for ice cores obtained
from the Greenland and Antarctic ice sheets and from alpine
glaciers at lower latitudes.
– Ice cores are used to obtain temperature data from isotope
ratios, and provide information on the past chemistry of the
atmosphere and on the incidence of past volcanic eruptions.
Methods for Determining Past Climates
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• Remnant Landforms
– All of Earth’s landforms are the end result of processes that
build up and wear down features at the surface.
– Mechanisms for eroding and depositing material include the
movement of water, the slow-moving ice sheets expanding
across the surface, wave action along coastlines, wind, and
floating icebergs carrying land debris.
– These mechanisms leave characteristics that scientists can
use as evidence to infer climatic conditions at the time of
erosion or deposition.
Methods for Determining Past Climates
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• Past Vegetation
– When vegetation occupies a region, some of its pollen and
spores can be deposited and preserved indefinitely in lake
beds or bogs.
– Much information about past climates extending back for
several thousand years can also be obtained from tree rings.
Methods for Determining Past Climates
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• Past Vegetation
Methods for Determining Past Climates
Gran Edel-
gran Starr Furu Or
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Methods for Determining Past Climates
• Past Vegetation
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Past Climates
• Earth scientists have devised a scheme to divide the planet’s
natural history into distinct time
frames.
• The geologic column uses a
hierarchical system dividing time
into eras, periods, and epochs.
• Segments are based on geologic and fossil evidence of past
environmental conditions and events.
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• Warm Intervals and Ice Ages
– Brief cold ice ages interrupted a generally warm climate,
about 10–20% of the time in the last 2.5 billion years.
– For most of Earth’s history, climate was 5–15°C warmer
than present.
– For 20,000 years, global temperatures warmed by more
than 5°C. Massive releases of carbon dioxide and
methane from multiple sources led to the so-called
Paleocene-Eocene Thermal Maximum (PETM,~55MYA).
– Perhaps nearly entire planet ice covered ~700 MYA
(“snowball Earth”)
Past Climates
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• Warm Intervals and Ice Ages
Past Climates
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Past Climates
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• The Pleistocene
– Oscillations between glacials and interglacials.
– Amplitude increasing, esp around 800,000 years ago.
– Short term oscillations superimposed on longer cycles.
– Last 2 My thee has been ~30 cycles, temperature
variations ~5°C.
– Ice sheets varied by a factor ~3 with each cycle, mostly in
the Northern Hemisphere.
– The Earth is now in a warm interglacial, rivaled only a few
times in the last 2 million years, e.g. 130,000 years ago
when global temperatures were 1-3°C warmer than now
and sea level 6 m higher.
– Since this warm period there has been a glaciation that
ended ~20,000 years ago.
Past Climates
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Past Climates
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• The Last Glacial Maximum
– There were two main pulses of glaciation, one about 115,000
years ago and another about 75,000 years ago.
– Most ice was added to polar caps during the first pulse and to
ice caps in North America and Eurasia during the later pulse.
– Most places were colder and drier.
– This glacial period was not uniform. Abrupt climate changes
were common, with polar temperatures changing by 8°C to
16°C over the course of just decades to centuries. SSTs
varied much less.
Past Climates
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• The Last Glacial Maximum
Past Climates
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• The Holocene
– Warming prior to Holocene (~15,000 years ago) followed by
cool period ~2,000 years later - Younger Dryas, lasting
~1,200 years
– Thereafter onset of Holocene with abrupt warming, ~1°C per
decade in Greenland.
– Little Ice Age spanning yr ~1400-1800 not a real ice age, but
the largest temperature change (minus 0.5-1°C) during
historical time.
• Largely independent regional climate changes, rather than a
globally synchronous increased glaciation. At most there was
modest cooling of the Northern Hemisphere (Europe, America)
during the period.
• Several causes have been proposed: cyclical lows in solar
radiation, heightened volcanic activity, changes in the ocean
circulation, an inherent variability in global climate, or decreases
in the human population.
Past Climates
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Past Climates
Various reconstructions. Heavy pink line considered most reliable.
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Past Climates
Wikipedia
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Past Climates
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• Written records provide direct and indirect evidence of
past volcanic eruptions.
• The densest and most persistent volcanic cloud on
record was observed in Europe and the middle east
during 536-537 CE.
• Procopius (Rome, 42°N):
The Sun gave forth it’s light without brightness, like the
Moon, during this whole year, and it seemed
exceedingly like the Sun in eclipse, for the beams it
shed were nor such as it is accustomed to shed.”
The Mystery Cloud of 536 CE
Toohey et al., 2016
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• Zacharias of Mytilene (Constantinople 41°N):
The Sun began to be darkened by day, and the Moon
by night, from the 24th of March in this year till the 24th
of June in the following year.
• John of Ephesus (probably, Mesopotamia, 30-37°N)
… the Sun was dark, and its darkness lasted for 18
months; each day it shone for about 4 hours, and still
this light was but a feeble shadow… the fruits did not
ripen and the wine tasted like sour grapes.
The Mystery Cloud of 536 CE
Toohey et al., 2016
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Stra
tosp
her
e Tr
op
osp
her
e
Stratosphere → troposphere transport
Scavenging
Deposition
Surface cooling
SO2 injection Sulfate aerosols
LW absorption → warming
SW Reflection
Sulfate preserved in ice
Volcanic eruptions and climate
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Extreme climate of 536 CE
• Reports of “dry fog”, weak sun, cold temperatures and
ruined crops in Mediterranean
• “Failure of Bread” in Ireland, 536 and 549 CE
• Extraordinary coldness and heavy snowfalls in Baghdad,
winters 536 and 537
• Chinese scholars failed to observe the important
southern star Canopis in 536 CE
• In China, frosts and snow in July and August 536/537
which killed the seedling crops and caused major famine.
Toohey et al., 2016
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Climate in China ca. 536 CE (Wiseburd, 1985)
Early frost, drought,
famine 536 CE
Frost in 536 CE
Summer snow,
famine 537CE
Famine, 537 CE
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• One of the greatest plagues in history , afflicted the
Eastern Roman Empire (Byzantine Empire).
• Killed perhaps 40% of the population of Constantinople
and up to a quarter of the human population of the
eastern Mediterranean.
• Cause of the pandemic was Yersinia pestis, the
organism responsible for bubonic plague
• Genetic studies point to China as having been the
primary source of the contagion.
• The plague returned periodically until the 8th century.
The waves of disease had a major effect on the future
course of European history.
The Plague of Justinian (541–542)
Toohey et al., 2016
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• Tree-ring data suggest that this was the most severe and
protracted short-term cold episode across the Northern
Hemisphere in the last two millennia, even surpassing
the severity of the cold period following the Tambora
eruption in 1815.
Tree rings imply strong cooling
Larsen et al., 2008
Toohey et al., 2016
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536 double event
Toohey et al., 2016
• Double volcanic event, Toohey et al. 2016
– High or mid northern latitude eruption 536
– Low latitude event 540
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536 double event
Toohey et al., 2016
Model blue (ensemble),
treerings black
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• The Last Century
– Due to meteorological data/stations on the increase, more
climate data is available for the last century.
– Global warming is not the only climate trend in the last
hundred years.
– Precipitation exhibits variability from year to year and from
place to place. Long-term changes must be very large.
Past Climates
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• The Last Century
Past Climates
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Past Climates
• The Last Century
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Past Climates
• The Last Century
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• Effects of Warming on Temperature-Related Variables
– Number of days with frost has decreased over many parts of
the midlatitude regions.
– Decrease in extreme cold and extreme warm events have
become more frequent.
– Snow cover has decreased in most areas and has mostly
been driven by increasing temperature.
– From 1901 to 2002 the maximum extent of seasonally frozen
ground declined by about 7 percent in the Northern
Hemisphere.
Past Climates
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Factors Involved in Climatic Change
• Variations in Solar Output
– Solar output changes regularly.
• 0.1–0.2% change due to sunspots.
• 11-year cycle for sunspots.
– The Maunder minimum was a period of few sunspots and
lower solar activity around the year 1600.
• The Little Ice Age occurred during the Maunder minimum.
• Links to the quasi-biennial oscillation (QBO): changes in
stratospheric tropical winds associated with changes in
sunspots.
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• Changes in Earth’s Orbit
– Milankovitch cycles refer
to regular natural
variations in the Earth’s
orbit around the sun.
• Obliquity—41,000-year
period
Factors Involved in Climatic Change
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• Changes in Earth’s Orbit
– Milankovitch cycles refer
to regular natural
variations in the Earth’s
orbit around the sun.
• Eccentricity—100,000-
year period
Factors Involved in Climatic Change
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• Changes in Earth’s Orbit
– Milankovitch cycles refer to regular natural variations in the
Earth’s orbit around the sun.
• Precession—27,000-year period
Factors Involved in Climatic Change
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• Changes in Land Configuration and Surface Characteristics
– Plate tectonics gradually change the configurations of the
mountains and oceans.
– Mountain building and land erosion affect climate over
geologic time.
– Land use changes such as deforestation and desertification
change albedo, surface temperatures, and water balance.
Factors Involved in Climatic Change
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• Changes in Land Configuration and Surface Characteristics
Factors Involved in Climatic Change
150 MYA
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End Permian (250 Ma)
Roscher et al., 2011
Paleogeography, Paleoclomatology, Paleoecology
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End Permian (250 Ma)
Roscher et al., 2011
Paleogeography, Paleoclomatology, Paleoecology
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End Permian (250 Ma)
Roscher et al., 2011
Paleogeography, Paleoclomatology, Paleoecology
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The response of climatic belts to
temperature changes is different
when starting from warmhouse or
coldhouse conditions. The global
climate on a glaciated Earth is more sensitive to changes in the
atmospheric content of
greenhouse gases than a
warmhouse climate, due to a
strong feedback of ice-cover and albedo changes.
Roscher et al., 2011
Paleogeography, Paleoclomatology, Paleoecology
End Permian (250 Ma)
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Energy Transfer Processes
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• Changes in Atmospheric Turbidity
– Atmospheric turbidity refers to the amount of suspended
aerosols contained in the air.
– Major volcanic eruptions inject aerosols into the atmosphere
over days or weeks, leading to temporary climate cooling.
– Changes in atmospheric aerosols affect the amount of solar
energy that can reach the Earth’s surface (global dimming).
– Residence times of tropospheric aerosols is a few weeks.
– Residence times of stratospheric aerosols is a few years.
Factors Involved in Climatic Change
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Indirect aerosol effect
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• Changes in Atmospheric Turbidity
Factors Involved in Climatic Change
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• Changes in Radiation-Absorbing Gases
– Anthropogenic contributions of CO2 has resulted in an
exponential increase since the mid-19th century due to
fossil-fuel burning.
– Increased CO2 concentrations lead to increased atmospheric
absorption of IR radiation.
– Increased anthropogenic greenhouse gases in the atmosphere
can lead to increased atmospheric water vapor (the most
important greenhouse gas).
Factors Involved in Climatic Change
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Factors Involved in Climatic Change
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Factors Involved in Climatic Change
• Changes in Radiation-Absorbing Gases
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Defining Climate Change
• The Earth’s climate is a system that responds to the configuration of external factors, often called
boundary conditions.
• The external factors are driving climatic change, or acting as forcing agents.
• Climate changes on many different time scales.
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Feedback Mechanisms
• Feedback mechanisms are systems in which changes in one variable lead to changes in another.
• Feedback mechanisms can be:
– Negative: where the feedback acts to inhibit further change in
a variable.
– Positive: where the feedback acts to magnify further change in
a variable.
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• Examples of feedbacks
– Ice-albedo feedback (positive feedback)
– Ice cover affects global albedo
– Evaporation of water vapor (positive feedback)
– Water vapor is a greenhouse gas
– Ocean-atmospheric interaction (positive or negative
feedback)
– Ocean levels change through thermal expansion and glacial
melting
Feedback Mechanisms
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Defining Climate Change
These are regional examples. Normally feedback is used for global conditions.
In this context these examples are less obvious.
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Feedback Mechanisms
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Feedback Mechanisms
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Atmosphere—Ocean Interactions
• Identifying the Causes of Climate Change
– Observing changes to particular causes and in making
predictions about possible futures, climate science relies
heavily on so-called Atmosphere–Ocean General
Circulation Models (GCMs).
– GCMs are mathematical representations of the Earth
atmosphere–ocean–land system that run on supercomputers.
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Projecting Climate Changes
• Identifying the Causes of Climate Change
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• Predicted Temperature Trends Through the 21st Century
Projecting Climate Changes
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• General Circulation Models
– The average amount of warming predicted by the models for
three 20-year time periods.
– Research will help to better understand the impact of human
activity, and new information will be obtained to help better
understand climate change.
Projecting Climate Changes
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• Predicted Temperature Trends Through the 21st Century
Projecting Climate Changes
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