Earth Sciences 2240F/G Lecture Notes - Lecture 12: Equatorial Bulge, Radiative Forcing, Ocean Current
11 Jun 2018
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Chapter 12 Climate- The Basics
1.0 Introduction
2.0 Climate System
• components (ice, ocean, land surface, vegetation) of climate
system are interactive
• significant variation in one will result in a change to other
components- thus a climate change
• 3 major causes of climate change in earth’s history:
o changes in plate tectonics, changes in earth’s orbit and
changes in sun’s energy
• use word ‘forcing’ when refer to factors that cause climate change
and word ‘response’ to refer to variation in climate produced by the
forcing event
2.1 Tectonic Processes
• constantly being changed, resulting in changing earth’s geography
• circulation of ocean currents depends upon the location and
arrangement of continents
2.2 Earth Orbital Changes
• early 20th century, Milutin Milankovitch recognized and explained
three forms of variation in position of earth’s axis and its orbit
around the sun
• these variations can cause the amount of solar energy reaching
earth to vary by as much as 10%, thus obviously must have some
effect on climate
• first: earth’s orbit around sun varies in a systemic manner over
periods lasting 100,000 years
o at times it is highly eccentric, at other times it is almost
circular
• second: the amount of tilt of earth’s axis changes systematically
from 21.5 to 24.5 degrees in a pattern that repeats every 41,000
years
o a lower tilt means less radiation in the summer and more in
the winter in N Hemisphere (contrast of seasons reduced)
• Third: wobble of earth’s axis that results form the varying
gravitational pull of the sun and moon on earth’s equatorial bulge
causes changes in the direction of earth’s tilt
o Called precession, has a cycle of 26,000 years
2.3 Sun Energy Changes
• strength of sun has slowly increased throughout the years
• short term variations, called sunspots, result in variations in solar
radiation arriving on earth
2.4 Climate Change Responses
• way of thinking about how the climate system responds to forcing
factors is in terms of the time it takes the climate system to react
fully to some factor (response time)
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Chapter 12 Climate- The Basics
• closer a system is to its equilibrium position, the smaller the driving
force to push it along, and the longer it takes to change
• real world, climate forcing rarely acts in the on or off mode, the
oscillations are smoother
• Two important points about forcing and response:
o The rate of response of the climate system is fastest when the
climate system is farthest from the equilibrium it seeks
o The system has many components with different response
times; each responds to the same forcing at its own tempo
2.5 Climate System Feedbacks
• some interactions in climate system already in operation initiate
responses that may amplify whatever forcing is going on (positive
feedback) or may suppress the primary forcing (negative feedback)
o positive feedback example:
▪ decrease in the heat energy sent to earth by sun that is
sufficient enough that ice and snow spread across
regions at high latitudes that had not been covered by
them before
▪ because snow and ice reflect far more sunlight than
bare ground, any increase in the area they cover should
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