GEOL105 Chapter Notes - Chapter 12: Plate Tectonics, Coastal Erosion, Arctic Air
31 May 2018
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CH 12: Climate and Climate Change
12.1 Global Change and Earth System Science: An Overview
● Two central goals for the Earth sciences by Preston Cloud
○ Understand how earth works and how it has evolved from a landscape of barren
rock to the complex landscape dominated by the life we see today
○ Apply that understanding to better manage our environment
● The effects of human activity on earth are so extensive that we are actually involved in
an unplanned planetary experiment
● Earth system science: the study of earth as a system
○ Learning how various components of the system-the atmosphere, oceans, land,
and biosphere-are linked on a global scale and interact to affect life on earth
● A major goal is to predict future changes that are relevant to society and people today
12.2 Climate and Weather
● Climate: refers to the characteristic atmospheric conditions of a given region over long
periods of time, such as years or decades
○ More than just avg high and low temps and/or amt of rainfall at a given location
○ The simplest classification is by temperature and precipitation
● Weather: refers to the atmospheric conditions of a given region for short periods of time,
such as days or weeks
● Climate exerts a major influence on natural processes
● Flooding is in part dependent on rainfall amount and intensity, landslides may be more
common in areas with rainy climates
12.3 The Atmosphere and the Cryosphere
● Atmospheric composition
○ Permanent gases: compounds that form a constant proportion of the mass of
the atmosphere (comprise about 90% by volume of all atmospheric gases)
■ Nitrogen (78.08%)
■ Oxygen (20.95%)
■ Argon (0.93%)
○ Variable gases: gases whose proportions vary in time and space (such as
carbon dioxide)
○ Aerosols: microscopic particles whose proportions also vary in time and space
● Cryosphere: the portion of a planet consisting of ice; on earth this includes permafrost
in soil and below the seafloor, glaciers, ice sheets, ice caps and fields, ice shelves, and
icebergs
● The ice in permafrost, sea ice, and ice caps is either fixed in place or floating
● Glacier: an accumulation of ice, snow, rock, sediment, and liquid water that flows from
high to low areas due to gravity acting on the weight of this accumulated ice
● Glaciers and ice sheets have budgets with inputs and outputs
○ Inputs consist of new snow recrystallizing to form ice at higher elevations
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○ Outputs occur at lower elevations where ice is lost by melting, evaporation, and
blocks breaking off the front of the glacier or ice sheet
● Over the past 3.2 million years, Earth’s climate system has fluctuated greatly and
alternated between periods of major continental glaciation referred to as glacial
intervals, and times of warmer climate with significantly less glaciation, referred to as
interglacial intervals
○ Today we live in interglacial conditions
● Ice sheet advances and retreats, or growth and melting back of glacial ice, have been
relatively rare during earth’s history
● The last series of glacial and interglacial intervals took place during the Pleistocene
Epoch
● When glaciers move from the land into the sea, large blocks of ice break off from the
front of the glacier and drop into the water in a process known as calving
○ Produces blocks of floating ice, known as icebergs, which can float into shipping
lanes and create a hazard to navigation
12.4 How We Study Past Climate Change and Make Predictions
● Data are available for three main time periods:
○ The instrumental record- starting at about 1880, temp measurements have been
made at various locations on land and in the oceans; earliest records are from
the late seventeenth and early eighteenth centuries; today, the temp is measured
at about 7000 stations around the world; the concentration of carbon dioxide in
the atmosphere has been measured since about 1960
○ The historical record- a variety of historical records go back several hundred
years; included are people’s written recollections of the Medieval Warm Period
and the Little Ice Age, as well as ships’ logs, travelers’ diaries, and farmers’ crop
records; not generally quantitative data
○ The paleo-proxy record- proxy data (refers to the data that are not strictly
climicatic but can be correlated with climate, such as temp of the land or sea);
some info gathered as proxy data includes natural records of climate variability,
as indicated by tree rings, ocean sediments, ice cores, fossil pollen, corals, and
carbon-14; provide the best evidence of a change that predates the historical and
instrumental records
● Various data sources for paleo-proxy records
○ Tree rings
■ Most trees put on one growth ring a year
■ The width, density, and isotopic composition of annual rings provide
information about past climate
○ Sediments
■ Sediment deposits are sampled and studied
■ Some of the strongest evidence for past climate change comes from
these proxy records
○ Ice cores
○ Pollen
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○ Corals
○ Carbon-14
○ Carbon dioxide
● Global climate models
○ From the 1980s the present, atmospheric general circulation models have been
couples with mathematical models or other earth subsystems
12.5 Global Warming
● Global warming: the observed increase in avg temp of the near-surface land and ocean
environments of earth during the past sixty years
● The greenhouse effect
○ Earth temp is determined by three factors: the amt of sunlight the earth receives,
the amt of sunlight earth reflects, and the amt of reradiated heat retained by the
atmosphere
○ Earth’s energy balance today is slightly out of equilibrium
○ Earth receives energy from the sun in the form of electromagnetic radiation
○ Water vapor and several other atmospheric gases tend to trap heat
■ As a result, the lower atmosphere of earth is much warmer than it would
be if all the infrared radiation escaped into space without this intermediate
absorption and warming
○ Most of natural “greenhouse warming” is due to water vapor and small droplets in
the atmosphere
● Since the Pleistocene ice ages began approx 2 million years ago, there have been
numerous changes in earth’s mean annual temperature
○ Low temps have coincided with major glacial events that have greatly altered the
landscape
○ High temps are associated with interglacial conditions
● There are cycles of change lasting 100,000 years, separated by shorter cycles of 20,000
to 40,000 years in duration
○ Milankovitch cycles
○ Not sufficient enough
● Climate forcing: an imposed change of earth’s energy balance
○ Units are W/m^2
○ Positive if a particular forcing increases global mean temp and negative if temp is
decreased
● Climate sensitivity: the response of climate to a specific climate forcing after a new
equilibrium has been established
○ Climate response time: the time required for the response to a forcing to occur
● Very short or abrupt climate change is unlikely
● Ocean conveyor belt (pg 420)
● Although scientific uncertainties exist, sufficient evidence exists to state that:
○ There is a discernible human influence on global climate
○ Warming is now occurring
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
12. 1 global change and earth system science: an overview. Two central goals for the earth sciences by preston cloud. Understand how earth works and how it has evolved from a landscape of barren rock to the complex landscape dominated by the life we see today. Apply that understanding to better manage our environment. The effects of human activity on earth are so extensive that we are actually involved in an unplanned planetary experiment. Earth system science: the study of earth as a system. Learning how various components of the system-the atmosphere, oceans, land, and biosphere-are linked on a global scale and interact to affect life on earth. A major goal is to predict future changes that are relevant to society and people today. Climate: refers to the characteristic atmospheric conditions of a given region over long periods of time, such as years or decades. More than just avg high and low temps and/or amt of rainfall at a given location.
