Earth’s Climate & Mankind
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Climate
 Long-term (years and longer)
average condition of a region
 Rainfall or snowfall
 Snow and ice cover
 Temperature
Weather
 Short-term (hours to weeks)
fluctuations
Historical Examples of Climate Change?
Advance and retreat of glaciers
th century
 Alpine glaciers shrunk in 20
 Thinning of ice on NW Greenland
 See Nature v. 414, 60-62
 Sea level rise
 El Nino/La Nina oscillations
 Length of growing season in Alaska
increased from 1950-2000
 Decrease in Arctic sea ice cover from
1970-2000
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How We Will Study Climate Change
Time Scales of Climate Change
Earth’s Climate System
Earth’s climate system
 Air, water, land and vegetation
 Changes in Earth’s climate system
 Driven by cause and effect
 Buzz words of climate scientists – forcing
and response
 Forcing – factors that drive or cause
changes
 Response – the climate change that
occurs

Earth’s Climate System and the
Interactions of its Components
Forcing & Response
Climate Forcing

Tectonic Processes
 Slow movement of plates affects climate
only very slowly
Climate Forcing

Earth-Orbital Changes
 Variations in earth’s orbit around the
Sun affect the amount of solar radiation
received on Earth’s surface. Orbital
scale changes occur over tens to
hundreds of thousands of years.
Climate Forcing

Changes in the Strength of the Sun
 Affects the amount of solar radiation
received on Earth’s surface. Can occur
on long-term (100’s of millions of years)
or on short-term (10-1000’s years)
Climate Forcing

Anthropogenic Forcing
 Not part of the natural climate system
 Affect of humans on climate
 Byproduct of agricultural, industrial and
other human activities
 Example is addition materials to the
atmosphere such as gases (CO2, N2O,
etc.), sulfate particles and soot.
Response Time

Time it takes the climate system to react
to a change in forcing (reaction time)
Response time = amount of time it takes
to get 50% of the way toward equilibrium
Response Time
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Response curve exponential
 System moves ½ the way to equilibrium with each
passage of response time
Absolute amount of change decreases through time but
proportional change towards equilibrium is constant
Time Scale of Forcing vs. Response

Forcing is slow compared to response
 Climate system tracks forcing
 Typical of climate change on tectonic time
scales
Time Scale of Forcing vs. Response

Forcing is fast compared to response
 Little response to climate forcing
 Stochastic events with short-lived response
Time Scale of Forcing vs. Response

Time scale of forcing = response time
 Yields dynamic and realistic response
Frequency of forcing
has a direct effect on
the magnitude of the
response
The time scale of
forcing is not long
enough to allow the
system to reach
equilibrium
Cyclic Forcing and Response
Natural climate forcing may vary in a
cyclic fashion producing cyclic response
 Response time same; forcing is changing

Cyclic Forcing and Response
Since forcing is constantly changing,
equilibrium value of system also changes
 Equilibration values set by the rate and
direction of change of the forcing
 Regardless of the forcing rate of change
 Response rate of the system is is
fastest when the system is furthest
from equilibrium

Cyclic Forcing and Response

Frequency of forcing
affects the amplitude
of the response
 Slower cycling
produces a larger
response – more
time to react
 Faster cycling
produces a smaller
response – less
time to react
Cyclic Forcing and Response

Cycling forcing and response typical of
Milankovitch type orbital cycles
 Changes in incoming solar radiation due
to changes in Earth’s orbit occur
cyclically over tens of thousands of
years
 Response time of large glacial ice sheets
also tens of thousands of years
Response Rates & Interactions

Different components
of the climate system
have different
response times
 Different
components will
respond to a change
in forcing at
different rates
Response Rates & Interactions

If climate forcing occurs in cycles, it will produce
different cyclic responses in the climate system
 Fast responses track forcing
 Slow responses lag forcing
Response Rates & Interactions

What happens to air temperature near the
foot of the glacier if incoming solar
radiation were to slowly increase?
Interactions in the Climate System
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Does the air warm due
to increase in solar
luminosity?
Does the air stay cool
because of the
proximity to large
mass of glacial ice?
Response time of air
influenced by both
 Response time of
air will be faster
than the response
of the ice but lag
behind forcing
from the Sun
Interactions in the Climate System
Individual components within the climate
system do not respond passively to forcing
 Dynamic interaction between systems
 Interaction blurs the distinction between
forcing and response
 Difficult to determine what system or
systems are reacting to the forcing

Feedbacks in the Climate System

Interactions can
produce positive
feedback
 Positive feedbacks
produce additional
climate change
beyond that
triggered by the
initial forcing
 Positive feedback
amplify changes
Feedbacks in the Climate System

Interactions can
produce negative
feedback
 Negative feedbacks
reduce the response
that would be
caused by the
forcing
 Negative feedback
suppress climate
change