Earth

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Earths Climate and Climate Change
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Weather and Climate
What is weather? Weather is the state of
atmospheric conditions (i.e., hot/cold, wet/dry,
calm/stormy, sunny/cloudy) that exist over
relatively short periods of time (hours to a
couple of days). Weather includes the passing of
a thunderstorm, hurricane, or blizzard, and the
persistence of a heat wave, or a cold snap. What
is Climate? Climate is the weather we expect over
the period of a month, a season, a decade, or a
century. More technically, climate is defined as
the weather conditions resulting from the mean
state of the atmosphere-ocean-land system, often
described in terms of "climate normals" or
average weather conditions. Climate Change is a
departure from the expected average weather or
climate normals.
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Factors That Determine Climate
The Earth is cold at the poles and warm at the
equator
Sun light is incident on the Earth at steeper
angles in the polar regions. Sunlight falling at
an angle is spread out over a greater area and
therefore causes less heating.
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Factors That Determine Climate

• Tilt of the Earths axis
• 23.5? towards the sun in summer
• 23.5? away from the sun in winter
• Polar regions become extremely cold in winter.
• Even though the poles get constant sun in summer,
  the solar angle is so low that the heating is
  small. Also, polar ice reflects sunlight,
  further reducing the effect of constant sun.

Solar energy absorption
Solar energy reflection
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Factors That Determine Climate
Latitude Warm and moist at the equator, cold
and dry at the poles Altitude Higher altitudes
are colder and dryer Proximity to oceans Oceans
moderate temperature and increase humidity Local
terrain Mountains can cause clouds an
precipitation on the windward side, and dry
conditions on the leeward side
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The climate where you live
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Climate Data

• Direct Measurements
• Observations of air water temperature,
  precipitation amount, etc have been made
  routinely with accurate instruments for about 150
  years
• Historical Records
• Clues left in written documents from the past
• Paleoclimate
• Properties of the Earth and Atmosphere are
  determined from clues hidden in the Earth, a
  kind of forensic science.
• Sources of paleoclimate information
• Ice Cores
• Tree Rings
• Ocean Sediment

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Ice Cores

• Ice cores are samples of ice taken from glaciers
  .
• Air bubbles, dust, and oxygen isotopes get
  trapped in glacial ice, and can be used to
  analyze past climate.
• Glaciers become thicker over time, so the deeper
  you drill the older the ice is.
• Glaciers obtain one layer each year, so counting
  layers is like counting years.
• Ice core data can extend back hundreds of
  thousands of years
• Ice cores can reveal temperature, precipitation,
  and gas composition of the lower atmosphere
• They also can indicate volcanic eruptions, solar
  variability, sea-surface productivity and a
  variety of other climate indicators.

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Ice Cores
Climate related parameters determined from ice cores Climate related parameters determined from ice cores
Ice Core Property Climate Parameter
CO2, CH4 Greenhouse gasses
SO2, ash Volcanic eruptions
Be10, Cl36 Solar activity
O18/O16 , deuterium Temperature
thickness Precipitation
Deuterium (a hydrogen isotope) can be used to
reconstruct past temperature changes. In
Antarctica, a cooling of 1C results in a 9 ppm
decrease in deuterium.
The ratio of oxygen isotopes, O18/O16, in ice is
an indication of temperature change. Smaller
values of O18/O16 indicate warmer temperatures.
Changes over 200 millennia from Greenland ice
cores
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Tree Rings
In temperate regions where there is a distinct
growing season, trees generally produce one ring
a year Since tree growth is influenced by
climatic conditions, patterns in tree-ring
widths, density, and isotopic composition reflect
variations in climate.  Trees can grow to be
hundreds to thousands of years old and can
contain annually-resolved records of climate for
centuries to millennia. If a tree is fossilized,
the age of the tree (how long ago it died) can be
determined by examining isotopes. Isotope ratios
are also indicative of temperature change.
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Ocean Sediments
Billions of tons of sediment accumulate in the
ocean and lake basins each year. Scientist drill
cores of sediment from ocean and lake floors.
Ocean and lake sediments include tiny fossils
and chemicals that are used to interpret past
climates.
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The Greenhouse Effect
The Earth receives ultraviolet (UV) radiation
from the sun, absorbs it, and then radiates the
energy out as infrared radiation If the Earth
behaved as a simple blackbody then the Earths
average temperature would be 18? C
However, the Earths average temperature is 15?
C. The Earth is warmer because our atmosphere
traps some of the outgoing IR radiation. This
is a natural process known as the greenhouse
effect. The greenhouse effect is a good thing,
without it the Earth would become too cold for
life to exist. However, mans activities appear
to be altering the natural balance.
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The Greenhouse Effect
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Greenhouse Gasses

• Greenhouse gases are atmospheric gases that trap
  infrared radiation emitted from the earth.
• Most of the significant greenhouse gases are
  long-lived and well-mixed
• Long-lived means they are chemically stable and
  therefore last years in the atmosphere
• Well-mixed means they are evenly distributed in
  the atmosphere.
• This family includes carbon dioxide, methane,
  oxides of nitrogen, and halocarbons.
• Water vapor is a greenhouse gas that is neither
  well-mixed nor long-lived. Because of this, its
  overall effect on global warming is the least
  understood.

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Greenhouse Gasses

• Factors that determine the importance of a
  greenhouse gas
• Atmospheric abundance
• The wavelengths of radiation absorbed
• The efficiency of radiation absorption

Greenhouse Gas Concentrations Greenhouse Gas Concentrations Greenhouse Gas Concentrations Greenhouse Gas Concentrations
Greenhouse gas Concentration 1750 Concentration 1995 Percent Change
Carbon dioxide, CO2 280 ppmv 360 ppmv 29
Methane, CH4 0.7 ppmv 1.7 ppmv 143
Nitrous oxide, N2O 280 ppbv 310 ppbv 11
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Carbon Dioxide (CO2)

• CO2 accounts for 55 of the global warming
  effect.
• Natural sources of CO2
• Respiration all living organisms respire and
  give off carbon dioxide.
• Decomposition of organic material
• Anthropogenic sources of CO2
• Fossil fuel burning (65)
• deforestation and burning of rain forest
• land-use conversion
• cement production
• Anthropogenic sources account for most of the CO2
  produced annually.

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Carbon Dioxide (CO2)
CO2 in the atmosphere is increasing dramatically
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Methane (CH4)

• CH4 accounts for 20 of the global warming
  effect.
• Natural sources of CH4
• produced as a result of microbial activity in the
  absence of oxygen.
• Natural wetlands or bogs
• Termites
• Anthropogenic sources of CH4
• Rice paddies
• Cattle
• Drilling for oil
• Landfills
• Biomass burning
• Coal mining.
• Anthropogenic sources account for 70 of the
  methane produced annually.
• methane oxidizes with OH to become water CH4
  OH gt CH3 H2O

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Methane (CH4)
CH4 concentration in the atmosphere are
increasing dramatically
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Global Temperature ChangeFrom Direct Measurements
Temperature change is often reported as the
temperature anomaly, which is the temperature
compared to the average over some time
period. Below, global average temperatures are
compared to the average temperature during 1951
1980.
Global average temperatures, relative to the
1951-1980 average (about 14C)
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Global Temperature ChangeFrom Direct Measurements

• 1998 saw the 20th straight year of above-normal
  surface temperatures.
• 1998 was the hottest year since the mid-1800s,
  global temperatures were 1.04 degrees F above
  average.
• The 10 warmest years in the 150-year history of
  recorded temperatures have all occurred since
  1983.
• In Alaska and other polar regions, the permafrost
  is melting and whole forests are dying due to an
  increase of insects associated with warming
  temperatures.

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Global Temperature ChangeFrom Proxy Measurements
Global temperatures determined from ice cores and
other paleoclimate records indicate that the
Earths temperature was fairly constant until
recently
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Global Climate Models (GCM)

• GCMs are computer models that simulate the
  Earths climate
• They calculate a variety of things including
• Air temperature
• Sea level
• Sea temperature
• Glacier size and thickness
• GCMs consider the Earths surface, oceans, and
  atmosphere
• How they behave and how they interact with each
  other
• Why use GCMs?
• The Earth-Ocean-Atmosphere system is extremely
  complex
• Understand current climate
• Predict future climate

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How well do GCMs perform?
One test is to see if GCMs can simulate what has
already happened
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Global Temperature Change Past - Future
GCMs predict drastic warming if nothing changes
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Indications of Global Warming
Melting of polar ice Glaciers in southeastern
Greenland are thinning by more than 3 feet a
year Rise in sea level Water expands as it
warms Melting glaciers Enhanced plant
growth Plants need CO2 for photosynthesis Warmer
temperatures Longer growing seasons
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The EndExtra slides follow
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Ice Cores
Ice cores can reveal temperature, precipitation,
and gas composition of the lower atmosphere They
also can indicate volcanic eruptions, solar
variability, sea-surface productivity and a
variety of other climate indicators. More on
the relationship between glacier depth and time
Depth is related to time, glacial ice
accumulates one layer per year. Accumulation
rates inferred in this way are supported by
measurements of beryllium 10 (Be10). Be10 is an
isotope produced by the interaction of cosmic
rays and the upper atmosphere. The deposition
rate of Be10 can be assumed constant.
Therefore, the amount of Be10 in ice is related
directly to time.
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Global Climate Models (GCM)
GCMs come in a variety of types Atmosphere
general circulation models (AGCMs) consist of a
three-dimensional representation of the
atmosphere coupled to the land surface and
cryosphere AGCMs coupled to a 'slab' ocean This
type of model predicts changes in sea-surface
temperatures and sea-ice by treating the ocean as
though it were a layer of water of constant depth
(typically 50 metres) Ocean general circulation
models (OGCM) a three-dimensional
representation of the ocean and sea-ice Carbon
cycle models describe several important climate
feedbacks on carbon dioxide concentration, for
instance fertilization of plant growth by carbon
dioxide and uptake or out gassing of carbon
dioxide by the oceans Atmospheric chemistry
models calculate chemical reactions that
determine the production or destruction of
important species such as ozone and
methane Coupled atmosphere-ocean general
circulation models (AOGCMs) the most complex
models in use, consisting of an AGCM coupled to
an OGCM. AOGCMs can be used for the prediction of
future climate.