Ch 23. Global Climate Change
Fig. 23.3
Fig. 23.9
Greenhouse effect
See Fig. 23.6
•Sunlight enters the atmosphere
•Radiation is backscattered in the form of longer wavelength
radiation (infrared). Atmosphere works like the lid of a greenhouse.
•The more greenhouse gases, the more this heat radiation is trapped
in the atmosphere, warming air and Earth’s surface.
Effect of greenhouse gases
 Without greenhouse gases, earth’s mean
temperature would be 33°C colder (today’s mean
temp of 15°C compared to -18°C).
 In earth’s climatic history, cold (glacial) and warm
(interglacials) stages have always been
accompanied by low (180 ppmv) and high (280
ppmv) CO2 levels, respectively.
Anthropogenic gases that
contribute to the greenhouse effect
Greenhouse Gas
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
Tropospheric ozone (O3)
CFC-11
CFC-12
Relative contribution
60%
15%
5%
8%
4%
8%
Carbon dioxide is increasing in
the atmosphere
• As a result of human activities, carbon dioxide in the
atmosphere has increased by 30% since 200 years ago
See Fig. 23.8
Reasons for the rise in greenhouse gases:
Burning of fossil fuels (oil, coal and natural gas)
release 5.5 Gt of carbon into the atmosphere per year
1.6 Gt C is released due to slash and burn practices in tropical
rain forests.
The anthropogenic carbon budget
1980-89 (IPCC, 1995)
(Units are GtC/yr; uncertainties are 95% Confidence Limits)
•
Carbon Dioxide Sources
•
•
•
(1)
(2)
(3)
•
Partitioning Among Reservoirs
•
•
•
(4)
(5)
(6)
Storage in the atmosphere:
Ocean uptake:
Uptake by Northern Hemisphere forest regrowth:
3.3 ± 0.2
2.0 ± 0.8
0.5 ± 0.5
•
(7)
Inferred sink [(3)- {(4)+(5)+(6)}]:
1.3 ± 1.5
Emissions from fossil fuel combustion and cement production:
Net emissions from changes in tropical land use:
Total anthropogenic emissions [(1)+(2)]:
5.5 ± 0.5
1.6 ± 1.0
7.1 ± 1.1
75% of CO2 is emitted by 25% of industrialized world population.
Earth’s average temperature is
rising
• Earth’s average surface temperature has risen
at least 0.6°C (1.1°F) in the last 130 years
6
5
4
3
2
1
0
Projection for global temperature rise until 2100:
1.4-5.8 °C (2.5-10.4 F) according to different climate
Models (see Fig. 23.17)
Projection for global temperature rise until 2100:
1.4-5.8 °C (2.5-10.4 F) according to different climate
Models (see Fig. 23.17)
What about CO2 changes in the past?
Climate is
recorded in
ice cores
Drilling of ice cores
Drilling at Vostok
(Antarctica)
Warming and cooling
phases in earth’s
history were always
accompanied
by CO2 changes.
But at least during the last
400,000 years have CO2
levels not been as high
as today.
CO2 in Earth’s climate history
Data from an ice core
Predicted changes with increased
greenhouse warming
• Higher than normal sea surface temperatures that affect
world climate
• Melting of polar ice caps and glaciers
• Increase in sea-level (coastal erosion, inundation, high
coast protecting coastal communities)
• More severe droughts (in subtropics) and increased
precipitation in higher latitudes
• Changes in water supply, quality, increased competition for
water
• Longer and more intense heat waves
• Shifts in ecological zones (distribution of plants and
animals, change in forests)
• Change in crop yields, irrigation needs
See Table 23.1
Global
sea level rise due
to global warming
50 cm until 2100
(avg.),
range: 20-96 cm
57% due to thermal
expansion
33% due to glaciers/ice
caps melting
Fig. 23.18
Melting of the north
polar ice cap.
Where does the CO2 go?
Ocean takes up about one third of anthropogenic
CO2. Both the physical and the biological carbon
pump is responsible for that uptake.
Uptake mechanisms of CO2 by the ocean
 The physical pump: Cold water that is saturated with
CO2 sinks from high latitudes (mainly North Atlantic,
Antarctica) to form deep water. This water is removed
from contact with the atmosphere for hundreds of years.
 Biological carbon pump is the particulate or dissolved
organic carbon that is produced in the photosynthetic zone
and ‘exported’ to deeper water layers and finally buried in
the sediment. About 10% leaves the mixed layer and is
called Export Production. This carbon is removed from
contact with the atmosphere for 100s of years. Only about
0.1 % of what is produced in the surface reaches the
sediment and is permanently buried (on geological timescales).
Atlantic Ocean
subsurface
water masses
North Atlantic Central Water
Conveyer-belt circulation
What happens if global conveyor is turned off?
See Fig. 16.28
A ‘switching off’ of the
global conveyor belt could
cause a sudden cooling of
higher latitudes and may have been
responsible for the cooling event of the Younger Dryas.
Biological Carbon Pump
Some species of
phytoplankton,
unicellular, microscopic
algae that conduct most
of the photosynthesis in the
ocean. They are only fractions
of a millimeter in size.
Ch 23. Global Climate Change
Geology and climate
Continental drift (Plate tectonics) may cause
continental masses to move over poles and cause
build-up of ice shields, increasing Earth’s albedo.
Increased albedo exerts a positive feedback on climate
cooling (i.e. enhances cooling) by decreasing the
energy earth’s surface receives from the sun. Melting
of ice sheets due to global warming has the opposite
effect effect, decreasing albedo, and reinforcing global
warming by increasing the solar energy hitting Earth’s
surface.
Ch 23. Global Climate Change
Geology and climate
Plate tectonics also cause changes of ocean currents,
i.e. of continents block warm ocean currents to reach
higher latitudes, heat flux is diminished, temperature
differences between low and high latitudes increase.
Pols cool leading to a formation of ice caps and
climate worldwide cools (increased albedo will further
amplify this effect).
Ch 23. Global Climate Change
Geology and climate
Tectonic uplift (such as of the Himalayas and the
Tibetan Plateau) might have increased weathering
rates, which subsequently consumed CO2 from the
atmosphere, contributing to cooling and onset of
glaciations in the Pleistocene.
Ch 23. Global Climate Change
Geology and climate
Volcanic eruptions can temporarily cause cooling
bblocking solar radiation from entering
atmosphere, but in the longer term are as source of
CO2 and contribute to greenhouse gas blanket
enveloping Earth (increased volcanic outgassing
might have ended the global glaciation event of
the “Snowball Earth”, see Ch. 16).
Some conclusions...
• Atmospheric CO2 levels are rising to levels
unprecedented in recent climate history. This
greenhouse gas causes global warming and a rise in
sea level.
• The oceans mediate the atmospheric CO2 increase by
the action of the physical and biological carbon
pump, which absorb about one third of fossil fuel
CO2. Both are in turn subject to climate change.
• On long time-scales (>10,000 years) interaction of
lithosphere with cryosphere, hydrosphere and
atmosphere) have driven climate on Earth. That is,
until man arrived….
Some MCs...
Which of the following is the current warm
interglacial period?
A. Holocene
B. Miocene
C. Paleocene
D. Pleistocene
Some MCs...
Based on ice core data, how rapidly can Earth
shift from glacial to interglacial temperatures?
A. 10 to 30 years
B. 100 to 300 years
C. 1000 to 3000 years
D. 10,000 to 30,000 years
Some MCs...
How much did the average surface temperature
increase during the twentieth century?
A. approximately 0.3 °C
B. approximately 0.6 °C
C. approximately 1.2 °C
D. approximately 2.4 °C
Some MCs...
Which of the following processes removes
carbon from the atmosphere?
A. photosynthesis
B. respiration
C. volcanism
D. all of the above
Some MCs...
What proportion of the total amount of carbon
dioxide emitted into the atmosphere each year
stays in the atmosphere?
A. approximately 25%
B. approximately 50%
C. approximately 75%
D. approximately 100%
Some MCs...
Which of the following has dramatically changed
the carbon cycle over the past 150 years?
A. burial of organic carbon
B. burning of fossil fuels
C. deposition of carbon-rich sediments
D. volcanism
Some MCs...
By the end of the next century temperatures are
predicted to rise ________ because of global
warming.
A. less than 1.5 °C
B. 1.5 to 6 °C
C. 6 to 20 °C
D. greater than 20 °C
Some MCs...
Over the next century the warming and
expanding of oceans due to global warming
would result in a rise in sea level of as much as
____________.
A. 90 centimeters
B. 9 meters
C. 90 meters
D. 900 meters
Some MCs...
If all human activities that generated carbon dioxide
were to stop, how long would it take for atmospheric
carbon dioxide to return to its preindustrial level?
A. 2 months
B. 2 years
C. 20 years
D. 200 years
Some MCs...
How has the concentration of carbon dioxide in the
atmosphere changed since the start of the Industrial
Revolution?
A. Carbon dioxide concentrations have increased 3%.
B. Carbon dioxide concentrations have increased 10%.
C. Carbon dioxide concentrations have increased 30%.
D. Carbon dioxide concentrations have increased
100%.
Some MCs...
If Earth’s atmosphere did not contain greenhouse gases,
the Earth’s surface would be __________.
A. approximately 33 °C cooler
B. approximately 10 °C cooler
C. approximately 10 °C warmer
D. approximately 33 °C warmer
Some MCs...
The greenhouse effect is caused by __________.
A. carbon dioxide and water vapor that trap heat
radiating from the Earth’s surface
B. heating of homes and businesses, which releases
excess heat into the atmosphere
C. oceans that trap heat radiating from the Earth's
seafloors
D. too many plants on the surface of the Earth, which
prevent cooling of the surface
Some MCs...
Chemical analysis of ice cores demonstrates that as
temperature increases, concentrations of atmospheric
__________.
A. carbon dioxide and methane both decrease
B. carbon dioxide decreases while methane increases
C. carbon dioxide increases while methane decreases
D. carbon dioxide and methane both increase