Chapter 14: Climate Change
The earth’s changing climate
Possible causes of climatic change
Global warming
The Earth’s
18,000 years ago
• The earth’s climate is
always changing
• 18,000 years ago the
sea level was so low
that the English
Channel didn’t
even exist, and
Bering land bridge did
Determining Past Climates
1) fossil evidence
Q1: if fossil pollen of a tundra plant is collected in a layer of
sediments in New England and dated to be 12,000 years old, it
would suggest that compared with today, the climate then is
a) much colder, b) much warmer, c) similar, d) unknown
2) Ocean floor sediment oxygen isotope ratio (of oxygen 18 over
oxygen 16)
• Isotopes are atoms whose nuclei have the same number of
protons but different numbers of neutrons.
• This ratio is higher during a colder climate
3) dendrochronology- tree ring growth depends on
temperature and precipitation over certain regions
Q2: Which university established the dendrochronology
field first?
a) U. of Arizona; b) Harvard;
c) Stanford; d) Yale
Determining Past Climates
sediment cores: ocean, lake
ice cores: Antarctic, Greenland
borehole temperature profiles
Dating calcium carbonate layers of stalactites in caves
As the global warming debate has intensified in recent
years, many methods of reconstructing past climates
have undergone close scrutiny
Q3: What is the main uncertainty of these proxy data in
representing temperature?
a) relation is not linear
b) non-temperature effects are not easy to separate
c) correlation is not causality
d) all of them
Climate During
Past 1000 Years
and since 1860
“Hockey Stick” graph
The global warming of the
past 100 years has not
been constant
Q4: is the temperature
decrease from 1940-1970
contradictory with global
a) yes; b) no
Climate Change and Feedback
• Feedbacks cause climate changes to be either amplified
(positive feedback) or reduced (negative feedback).
Q5: The water vapor-greenhouse feedback is?
a) positive feedback;
b) negative feedback
c) unknown
Q6: Why is the snow-albedo feedback positive?
A: increasing T decreases snow cover; this decreases surface
albedo and hence increases surface solar absorption; leading to
further increasing T
Q7: why is cloud feedback overall negative?
A: low clouds are negative by reflecting solar radiation; high
clouds are positive just like greenhouse gases; overall low
clouds are more dominant, leading to overall negative feedback
Possible Causes of Climate Change
external: changes in incoming solar radiation
external (e.g., volcano) or human (e.g., CO2): changes in the
composition of the atmosphere
external (e.g., mountain uplifting) or human (e.g., land use in
urban and agricultural areas): changes in the earth’s surface
• Emissions of CO2 and other greenhouse gases are
by no means the only way to change the climate.
Climate Change and Atmospheric
Particles (decadal-century)
Q8: why does volcano eruptions, rich in sulfur, cool the
atmosphere in general?
A: sulfur aerosols reflect solar radiation; they also modify
clouds by increasing the cloud’s reflectivity
• Sulfate aerosols cool the climate and therefore
counteract global warming to some extent.
Climate Change and Variations in
Solar Output (decadal-century)
Sunspots: are huge magnetic storms on the sun that show up
as cooler (darker) regions on the sun’s surface
Q9: why does solar
radiation increases
with the increase of
sunspot numbers?
A: sunspots are cooler;
but the surrounding
margins of sunspots
are brighter (i.e.,
hotter); overall effect
is to increase solar
Climate Change and Variations in the Earth’s
Orbit (10K-100K years)
Milankovitch theory:
- eccentricity: geometry of orbit
(100K yr)
- obliquity: tilt angle of axis (41K yr)
- precession: direction of axis (23K yr)
Min: 22o
Max: 24.5o
Climate Change, Plate Tectonics,
and Mountain-Building (100M yr)
theory of plate tectonics
Landmasses 150M years ago
Earth’s land mass in 650 million years:
Q10: what are the external causes of climate change?
a) solar radiation change;
b) air composition change;
c) earth’s land mass change; d) all of them
Q11: with the change of earth’s axis in 11K years (due to
precession), current July in northern hemisphere would be
a) spring; b) summer; c) fall;
d) winter
Q12: How do major volcanoes change surface temperature?
a) decrease; b) no change; c) increase
Q13: Since the sunspot number is below average in 1986, the
solar radiation that year is
a) below average; b) normal;
c) above average
Warming is
Rising sea
Reductions in NH
snow cover
And oceans..
And upper
Human and Natural Drivers of Climate
CO2 is causing the
bulk of the forcing
On average, it lives
> 100 years in the
atmosphere and
therefore affects
climate over long
time scales.
without air, the
earth surface
temperature would
be much colder
Human and Natural Drivers of Climate
Q14: Since the radiative
forcing due to CO2 is nearly
the same as the total forcing
in the figure, can we claim
that only CO2 is important?
a) yes;
b) no
Natural versus human-caused
temperature increase
Climate models are needed:
land processes;
Understanding and Attributing
Climate Change
warming is
discernible on
all inhabited
Expected for all
Natural forcing
Q15: Does the figure prove that the global warming
is man-made?
a) yes; b) no
What’s in the pipeline and what could come
Warming will increase if GHG increase. If GHG were kept
fixed at current levels, a committed 0.6°C of further
warming would be expected by 2100. More warming
CO2 Eq
would accompany more emission.
3.4oC = 6.1oF
2.8oC = 5.0oF
1.8oC = 3.2oF
0.6oC = 1.0oF
A1B is a typical “business as usual” (2090-2099)
scenario: Global mean warming 2.8oC;
Much of land area warms by ~3.5oC
Arctic warms by ~7oC; would be less for less emission
Q16: will the world actually warm this much?
a) yes;
b) no
Q17: What is a possible reason?
a) volcano, b) earthquake, c) orbital change, d) axis change
What else happens in a hotter world?
Observations of sea level rise from
satellites, 1993-2003.
Q18: what are the reasons for the sea
level rise?
a) expansion of warmer ocean,
b) glacier melt;
c) both
Future changes just from these
processes could be up to 1.5 feet
(0.5 m) by 2100, and up to 3 feet
(1 meter) within about 2-3
centuries, depending on how
much GHGs are emitted.
Other related issues
Tropical forest dieoff
Hurricane activities
Kyoto Protocol