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Climate change – “science catfight” or not?
The Record Of Climate Change

Proxy Data
Causes of climate change
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Natural
Anthropogenic
Milankovitch cycles
Eccentricity 100,000 yrs
Obliquity (tilt) 41,000 yrs
Precession (wobble) 26,000 yrs
Other factors

Solar energy output variability

Correlations with sunspot cycles
Variations < 0.1% of irradiance
Figure 21.21 (left)
Positive feedback mechanisms
Other factors

Continental position

Continents in polar regions promote ice sheet
growth
Other factors

Ocean current circulation patterns
Thermohaline circulation

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Temperature or salinity induced density
differences
Cold water sinks to bottom at high
latitudes
Restricted flow to poles may promote ice
sheet growth
Other factors

Changes in CO2

CO2 levels track ice
core temps
Other factors

Changes in CO2


CO2 levels track ice
core temps.
May be positive
feedback, slight
warming releases
CO2 from oceans,
causes further
warming…
Source: GRID/Arendal
Climate Variations and
Tectonics

These are linked in various ways

Plate motions mean moving large continental masses
around


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Move away from equator: more water to absorb solar
radiation near equator, overall warming
Move towards equator: less water, can cool
General change in ocean circulation patterns
Uplift of large mountains can change atmospheric
circulation
Opening of oceans mean large lava outputs

Likely add gases to aid warming through greenhouse effect
Recent
Times


Last 2 million
years, have
had several ice
ages
Most recent
peaked
~20,000 years
ago
Other factors

Volcanic activity

Suspended material reflects solar radiation
Mt. Pinatubo, 1991 (Photo: USGS)
Volcanoes and Climate

Large eruptions can put a lot of
ash into atmosphere


can reduce amount of sunlight
reaching ground surface and
cooling
Pinatubo eruption 1991

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
20 million tons of SO2 put in the
atmosphere
Reflected 2-4% of incoming solar
radiation
Led to average cooling of earth by
0.5-1°C that persisted for ~1-2
years
“Cloud” from Mt.
Pinatubo eruption
Temperature
change


1815 eruption of
Tambora volcano in
Indonesia lowered
global temperature
3°C
1816 know as “the
year without summer”
Source: NASA
But, volcanoes also emit CO2

Cretaceous warm period may have been caused
by large volcanic eruptions
Cretaceous chalks record expansion of marine life in warm climate
Human impact
Human Effects on the Carbon Cycle
Human activities release
~7.1 Gt* of carbon into
the atmosphere each year
New plant growth and
…yielding a net
Air-sea exchange atmospheric increase
removes ~3.8 Gt/yr
of ~ 3.3 Gt/yr.
Projected Changes in Global Temperature
Under Three Different Scenarios
Continued reliance on fossil fuels
increased reliance on nonfossil fuels
Rapid conversion
to cleaner and more
resource-efficient technologies
Range of
uncertainty
Likely temperature
change by the
end of the 21st
century, relative
to 1960-1990
A. Fossil-fuel
intensive world
B. More conservationoriented world
Consequences for sea level



Melting land
ice
Thermal
expansion of
water
>100 m rise
since last
glacial
maximum
Global warming is
projected to reduce the
north polar ice cap,
disrupting Arctic
ecosystems, but
possibly improving
navigation.
Land surface slope near shoreline influences effect of sea level change
Raisz
• Over next century, Arctic could warm by 3 - 5 ˚C (similar to last interglaciation)
• Last interglacial caused by changes in Earth’s tilt and orbit
• Next century changes due to increased CO2 in atmosphere
Figure 18.6
Why are these linked?
2005 study suggesting that hurricane intensity (more cat 4
and 5) has increased over last 15 years, corresponding to
~0.3° increase in temperature
Reducing greenhouse gases

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Conservation
Alternative
energy
Sequestration

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Biomass
Deep ocean
Geological
Deep ocean injection

Liquid CO2
denser than
water in cold
high
pressure
environment
Per capita
emissions
UNEP/GRID
Another example of human effect on atmospheric composition:
Ozone depletion


Ozone gas in smog : bad
Ozone in stratosphere: good


Protects from UV radiation which damages
cells
Depleted by reacting with human made
compounds (particularly CFCs)
Ozone hole
found near
Antarctica in
1985
Led to passage
of legislation
(Montreal
Protocol) to get
rid of CFCs
Projected Changes in Ozone Concentration
With and Without the Montreal Protocol