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Chapter 14 Notes
The Changing Climate
Glaciers Are Still Sculpting Mt. Rainier in Washington
Climate not only varies from place to place, but it is naturally variable
over time. Over the great expanse of Earth’s history, and long before
humans were roaming the planet, there were many shifts—from warm to
cold and from wet to dry and back again.
Although climate has a significant impact on people, people also have a
strong influence on climate. Climate changes in the geologic past were
natural variations, but today climate change is dominated by human
influences that are sufficiently large that they exceed the bounds of
natural variability.
Components of Earth’s Climate System
There is a climate system that includes the atmosphere, hydrosphere, solid
Earth, biosphere, and cryosphere.
The climate system involves the exchanges of energy and moisture that occur
among the five spheres. These exchanges link the atmosphere to the other
spheres so that the whole functions as an extremely complex interactive unit.
The climate system provides a framework for the study of climate. Changes in
the climate system do not occur in isolation. Rather, when on part changes,
the other components also react.
Temperature Variations over Past 40,000 Years
Detecting Climate Change
High-tech and precision instrumentation are now available to study the composition
and dynamics of the atmosphere, but in order to determine how Earth’s climate
changed in the past different tools must be used.
To understand past climate changes scientists must use indirect evidence. This
evidence comes from natural recorders of climate variability such as seafloor
sediments, glacial ice, fossil pollen, and tree-growth rings.
Paleoclimatology - the study of ancient climates; the study of climate and climate
change prior to the period of instrumental records using proxy data
The main goal of paleoclimatologists is to understand the climate of the past in
order assess the current climate and potential future climate in the context of
natural climate variability.
Past Climates Can Be Studied with Tree-Rings
Sources of Proxy Data
1) Seafloor sediment – seafloor sediments contain the remains of organisms
that once lived near the sea surface.
2) Oxygen isotope analysis – a measurement of the ratio between to isotopes
of oxygen: O-16 and O-18. This ratio tells climatologist something the
amount of fresh water present and temperature
3) Glacial Ice – the ice provides a detailed record of changing air
temperatures and snowfall.
4) Tree rings – characteristics of each ring reflect the environmental
conditions that prevailed during the year when the ring formed.
5) Fossil pollen – climate is a major factor influencing the distribution of
vegetation, so knowing the nature of the plant community occupying an
area is a reflection of the climate.
6) Corals – useful information on past climate conditions are determined by
analyzing the changing chemistry of coral reefs with depth
Past Supercontinent Pangaea
Natural Causes of Climate Change
Natural mechanisms of climate change are causes of change unrelated to
human activities and may include:
1) Plate tectonics – rearranging of Earth’s continents, moving them closer or
farther away from the equator or poles
2) Volcanic activity – changing the reflectivity of the atmosphere and reducing
the solar radiation that reaches the surface
3) Variations in Earth’s orbit – the natural, cyclic change in our planet’s orbit,
axial tilt, and wobble
4) Solar variability – variations in the Sun’s radiation output, and the effects
on radiation output by sunspots.
Rise in Atmospheric Carbon Dioxide since Industrial Revolution
Human Impact on Global Climate
Human influence on regional and global climate did not just begin with the
onset of the modern industrial period. There is evidence that people have
been modifying the environment over extensive areas for thousands of
years. These modifications include the use of fire, overgrazing of marginal
lands by domesticated animals, and the altering of ground cover (clear
cutting forests) for agricultural purposes.
Starting around the year 1800, humans started changing the composition of
the atmosphere by introducing massive quantities of carbon dioxide into the
atmosphere.
Americans Are Responsible for about 25 percent
of Greenhouse Gas Emissions
Carbon dioxide (CO2)is a product of combustion reactions that occur when fossil fuels are
burned. Fossil fuels in wood, coal, and the distillation products of petroleum (gasoline,
diesel fuel, heating oil).
Carbon dioxide is also a greenhouse gas, a gas that absorbs reflected energy traveling
from Earth’s surface back out into space. So, as the amount of CO2 increases the amount
of heat held in Earth’s lower atmosphere increases, and consequently, the average
surface temperature of Earth increases.
Global Temperature Changes
Data collected indicates that the increasing levels in carbon dioxide have
resulted in an increase of average global surface temperature. The data
includes:
1) Since 1850, twelve of the last thirteen years (1995-2007) rank among the
thirteen warmest
2) Global mean temperature is now higher than at any time in at least the
500 to 1,000 years
3) The average temperature of the global ocean has increased to depths of
at least 3,000 meters
Coal Mining and Oil Drilling Are Sources of Methane
Trace gases and global warming
The industrial and agricultural activities of people are causing the build-up of
several trace gases that may also play a significant role in the increase of
surface temperatures. These gases include methane, nitrous oxide, and
chlorofluorocarbons (CFCs).
1) Methane is produced by anaerobic bacteria in wet places--swamps, bogs,
rice paddies-- where oxygen is scarce, from mining and drilling processes,
and the guts of everything from termites to cattle.
2) Nitrous oxide has its source in the use of nitrogen-based fertilizers and in
high-temperature combustion of fossil fuels.
3) CFCs are not a natural component of the atmosphere, but are introduced by
human activities. The role of CFCs in the depletion of stratospheric ozone is
well known, but their role as a greenhouse gas has just recently been
recognized.
Springtime Breakup of Sea Ice near Antarctica
Climate-Feedback Mechanism
Climate is a very complex interactive physical system; when any component of the
climate system is altered, many possible outcomes must be considered. These
outcomes are called climate-feedback mechanisms.
One possible climate-feedback mechanism related to greenhouse gases:
1) Warmer surface temperatures increase evaporation rates
2) This results in more water vapor in the atmosphere. Water vapor is a
greenhouse gas.
3) So, with more water vapor in the atmosphere, the temperature increase caused
by CO2 and trace gases is reinforced.
Positive feedback mechanisms reinforce the initial change, while negative feedback
mechanism work to counteract the initial change.
Changes in Extent of Arctic Sea Ice at the End of the Summer Melting
Consequences of Global Warming
Predicting specific regional changes in climate is difficult because of
the complexity of the climate system. However, some possible
consequences of greenhouse warming include:
1) Altering the distribution of the world’s water resources
2) A significant rise in sea level
3) A greater intensity of tropical cyclones
4) Changes in the extent of Arctic sea ice and permafrost