climate changes: past and future - universitetet i oslo · –decrease in extreme cold and extreme...

© 2015 Pearson Education, Inc.

Climate Changes:

Past and Future

Chapter 16 Lecture

Redina L. Herman

Western Illinois University

Understanding

Weather and

Climate

Seventh Edition

Department of Geosciences www.ucalgary.ca

BLUE PLANET


WHITE PLANET


EMERALD PLANET

Department of Geosciences

EMERALD PLANET

History of the Biosphere

Fig 13

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)


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.


• 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.



• 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.



• 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.



• Past Vegetation


Gran Edel-

gran Starr Furu Or



• Past Vegetation


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.


• 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


• Warm Intervals and Ice Ages

Past Climates


Past Climates


• 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


Past Climates


• 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


• The Last Glacial Maximum

Past Climates


• 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


Past Climates

Various reconstructions. Heavy pink line considered most reliable.


Past Climates

Wikipedia


Past Climates

• 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

• 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

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

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

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

• 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

• 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

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

536 double event

Toohey et al., 2016

Model blue (ensemble),

treerings black


• 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



Past Climates


• 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


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.


• 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




– Milankovitch cycles refer

to regular natural

variations in the Earth’s

orbit around the sun.

• Eccentricity—100,000-

year period




– Milankovitch cycles refer to regular natural variations in the

Earth’s orbit around the sun.

• Precession—27,000-year period



• 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.



• Changes in Land Configuration and Surface Characteristics


150 MYA


End Permian (250 Ma)

Roscher et al., 2011

Paleogeography, Paleoclomatology, Paleoecology


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)


Energy Transfer Processes


• 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.



Indirect aerosol effect


• Changes in Atmospheric Turbidity



• 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).




• Changes in Radiation-Absorbing Gases


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.


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.


• 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


Defining Climate Change

These are regional examples. Normally feedback is used for global conditions.

In this context these examples are less obvious.


Feedback Mechanisms


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.


Projecting Climate Changes

• Identifying the Causes of Climate Change


• Predicted Temperature Trends Through the 21st Century



• 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.



• Predicted Temperature Trends Through the 21st Century


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