Transcript Weather, Climate, and Society

Weather, Climate, and Society
Spring 2012, Lecture 3
1
Weather
• Day to day record
 Temperature
 Precipitation
• Time scale is short
 One week typical
 Two weeks maximum
2
Weather Forecasting
• Weather results from a chaotic system
• No mathematical tools which can completely
predict the behavior of chaotic system exist
• The longer the term of the forecast the less
“skill” it exhibits
3
Forecast skill
• Skill refers to the ability of the forecast to
exceed chance variation
• Suppose that on a given day in Boca Raton the
long term average of rain on a particular day is
40%
 A forecast of rain or no rain one week in advance
of that date that is correct 40% of the time shows
no skill
 A forecast that is correct 60% definitely exhibits
some skill
4
Skill continued
• Forecasts one day in advance often show high
skill levels
• As the forecast period lengthens, errors in the
forecast multiply
• Eventually the forecast is entirely erroneous
5
Long-term Averages
• Long-term weather records can be used to
compute averages, which do have validity
• Example: we may the average temperature and
amount of rainfall by individual months
 Data like this show that there is much more
precipitation in South Florida between late May
and November than for the remainder of the year
 We can also find out the average temperature in
any given month - such data show that there is
considerable variation from year to year
6
Climate
• Climate encompasses the statistics of
meteorological elements in a given region over
long periods of time
• Meteorological elements may include:
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Temperature
Humidity
Atmospheric pressure
Wind velocity (speed and direction)
Rainfall rates and total amounts
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Temporal Scale of Climate
• Ranges from decades to far longer periods
• For the shorter term periods, we may have
accurate measurements, over periods up to 150
years, and sometimes longer
 Of course, modern instrumentation means that
modern data are generally superior to older data
o More precise ( tenths of a degree rather than a degree)
o Better time resolution
o New data – rainfall rate, not just total amount
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Climate Change
• A change in the statistical distribution of
weather over a period of time
 Ranges from decades to millions of years
• Can be a change in the average weather or a
change in the distribution of weather events
around an average (for example, greater or
fewer extreme weather events)
• May be limited to a specific region, or may
occur across the whole Earth
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Long-term Climates
• Climate data for periods exceeding that of
written records requires other sources of data
• Geologists and geochemists
 Coaxing information out of natural objects
o
o
o
o
o
Glacial ice
Stalagmites
Lake and marine sediment cores, etc.
Tree rings
Boreholes
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Palynology
• Study of contemporary and fossil palynomorphs, including pollen
• Palynomorph is a geological term used to describe a particle of a
size between five and 500 micrometers, found in rock deposits
(sedimentary rocks) and composed of organic material
• Palynology is used to infer the geographical distribution of plant
species
 Distributions vary under different climate conditions
 Distinctive pollen shapes and surface textures may be used to
differentiate between different plant species
 Outer surface of pollen is composed of a very resilient material, and
resists decay
 Changing climate conditions cause changes in plant communities,
which cause changes in the type of pollen found in different
sedimentation levels in lakes, bogs or river deltas
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Foram Fossils
• Foraminifera, ("hole bearers") or forams for short,
typically produce a test, or shell, which can have either
one or multiple chambers, some becoming quite
elaborate in structure
• About 275,000 species are recognized, both living and
fossil
• The diversity, abundance, and complex morphology of
forams mean that fossil foraminiferal assemblages are
useful for biostratigraphy, and can accurately give
relative dates to rocks
• Petroleum industry relies heavily on microfossils such
as forams to find potential oil deposits
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Fossil Foraminifera
• Calcareous fossil foraminifera are formed from elements
found in the ancient seas they lived in and are thus they are
very useful in paleoclimatology and paleoceanography
 They can be used to reconstruct past climate by examining the
stable isotope ratios of oxygen, and the history of the carbon
cycle and oceanic productivity by examining the stable isotope
ratios of carbon
 Geographic patterns seen in the fossil records of planktonic
forams are also used to reconstruct ancient ocean currents.
 Certain types of foraminifera are found only in certain
environments – these types can be used to figure out the kind of
environment under which ancient marine sediments were
deposited
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Modern Foraminifera
• For the same reasons they make useful
biostratigraphic markers, living foraminiferal
assemblages have been used as bioindicators
in coastal environments, including indicators
of coral reef health
• Because calcium carbonate is susceptible to
dissolution in acidic conditions, foraminifera
may be particularly affected by changing
climate and ocean acidification
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Calcareous
Foram
Image
• Image from the
National Geophysical
Data Center , Boulder
(a division of NOAA)
• Photograph from a
research paper by Dr.
William Ruddiman,
Lamont-Doherty
Earth observatory
• Note scale bar – 200
millionths of a meter
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Climate Records
• Reliable climate records only exist back to the
1880’s in general, although a bit further in
some localities
• In order to get long-term climate data, up to
tens or hundreds of millions of years,
geoscientists use climate proxies
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Climate Proxies
• Preserved physical characteristics of the past
that enable geoscientists to reconstruct the
climatic conditions that prevailed during much
of the Earth's history
• The study of past climates is known as
paleoclimatology, and involves systematic
cross-verification between proxy indicators
• Example proxies are discussed on subsequent
slides
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Tree Rings
• Dating by counting tree-rings, which
are added annually
• Comparison of a series of tree rings
from one tree with tree-ring libraries
for a particular area allows exact
dating of a sample
• Tree ring widths vary depending on
climate conditions
18
Geologic Materials
• Many geologic materials contain geochemical
evidence of past climate conditions
• Examples are shown on the following slides
19
Geologic Cores
• Collecting sediment core samples
on Dillon Reservoir. (Photograph
by Norman Spahr, U.S.
Geological Survey.)
• Core library,
University of
Kentucky
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Examination of Cores
• Scientists examining
cores
• This was part of a lab
tour in conjunction with
a PolarTREC
conference in May,
2010
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Ice Cores
• (above) Members of Lonnie Thompson’s field
team working to extract a freshly drilled piece
of ice core from the drill barrel on Coropuna
ice cap, Peru - David Umann, Mary Davis,
Vladimir Mikhalenko, and Patrick Ginot.
• (right) Lonnie Thompson examining an ice
core
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• Stalagmites are
cave deposits that
grow from the
floor upwards
• They are formed
by water dripping
from above and
evaporating
• They thus contain
a record of the
climate at the
surface when they
formed
Stalagmites
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Geochemical Studies
• Studies of rock and ice cores and stalagmites
are based on isotopic evidence
• Isotopes are varieties of a chemical element
which have the same number of protons, but
different numbers of neutrons, and thus have
different atomic weights, which are the sum of
the number of protons and neutrons
• One element often used is oxygen, the most
element on earth
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Oxygen Isotopes
• Oxygen occurs in three natural isotopes, 16O,
17O, and 18O
• The ratio of 18O/ 16O is measured using an
instrument called a mass spectrometer
• This ratio is dependent on the temperature at
the time the oxygen containing material was
formed
• Thus, 18O/ 16O is a proxy for temperature
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Use of Oxygen Isotope Ratios
• In rock cores, many sediments contain oxygen
containing minerals which can be used for
isotope studies
• Water ice is H2O, and thus contains ice
• Stalagmites are composed of calcium
carbonate, CaCO3, and thus contain oxygen
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Other isotope systems
• Carbon has two stable isotopes, 12C and 13C,
which are often used in climate studies
• Hydrogen has two stable isotopes, 1H and 2H,
and can be used for climate studies
• Since 1952, a radioactive form of hydrogen,
3H, has also been present on earth as a result of
nuclear bomb testing in the atmosphere
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Oxygen Isotope Diagram
• Data showing δ18O,
a measure of the
change in the 18O/
16O ratio used as a
temperature proxy
• Data is a climate
record for most of
the Cenozoic era (65
million years before
present to now)
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Climate Variations
• Systematic variations of climate throughout
time are obvious in the climatic studies
• For now, we will look at two very recent
examples, the Medieval Warm Period (aka
Medieval Optimum) and the Little Ice Age
• In the scheme of deep time (geologic time)
these are relatively insignificant, but they play
a role in human history
29
Medieval Warm Period - 1
• Extends from about 800-1300 A.D.
• Temperatures were perhaps as warm as today,
maybe a little warmer
• In Europe, it was a time of stable climates and
bountiful harvests
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Medieval Warm Period - 2
• The Vikings were active during this period
 In addition to raiding non-Scandinavian countries,
they also occupied and lived in Greenland
 End of the Norse occupation in Greenland
occurred around 1300, and coincides with the
onset of the Little Ice Age
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Medieval Warm Period - 3
• Elisabethkirche in
Marburg, Germany
begun in 1235
• Many gothic cathedrals
were built during this
period, perhaps in
tribute to a benolent
God
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Medieval Warm Period - 4
• In North America, conditions were different
• There was increasing drought over much of
North America
 The end of the Classic Mayan civilization, and the
abandonment of Anasazi pueblos in the American
southwest, correspond to the end of this climate
regime
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Little Ice Age - 1
• Extends from about 1300-1800 A.D.
• In Europe, it was at most 1°C cooler than the
“natural climate of the present”(say, around
1960).
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Little Ice Age - 2
• Climate became erratic
 Decades of cold might be followed by decades of
drought, or of warmth
 Precipitation could increase substantially for one
or more decades
35
Sun Spot Record
• Astronomers in both Europe and China report fewer
sunspots during the Little Ice Age
• One period, the Maunder Minimum (1650-1700), saw
no recorded sunspots, and was the coldest period in
Europe during the last 1000 years
• Solar radiation output is thought to vary with sunspot
activity, with more sunspots indicating greater solar
output
• The Medieval Optimum was probably the result of
slightly greater solar output
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Jared Diamond
Born 10 September 1937
• American scientist and nonfiction author whose work
draws from a variety of fields. He is currently
Professor of Geography and Physiology at UCLA
• Best known for the award-winning books The Third
Chimpanzee; Guns, Germs, and Steel; and Collapse
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Civilization and Climate Change
• We now know that many civilizations have come and
gone based on climate changes
• Diamond found that there is what he calls a five-point
framework of factors that may contribute to
environmental societal collapse
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Diamond’s Reasons
Civilizations Fail
1. Climate change
2. Hostile neighbors
3. Failure of trade partners (that is, alternative
sources of essential goods)
4. Environmental problems
5. A society's response to its environmental
problems, which involve overpopulation in
many cases
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Diamond’s Five-Point Framework - 1
• 1. Climate change
 Disappearance of the Norse from Greenland and
the Anasazi from the American Southwest
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Diamond’s Five-Point Framework - 2
• 2. Hostile neighbors
 Societies may be able to hold off neighboring
societies as long as they are strong, but succumb
when they weaken due to thing like environmental
damage or climate change
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Diamond’s Five-Point Framework - 3
• 3. Decreased support by friendly neighbors
 If one society collapses, it may no longer supply
things which are essential for nearby societies –
the collapse of the friendly society may be due to 1
or 2
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Diamond’s Five-Point Framework - 4
• 4. Anthropogenic environmental damage
 Deforestation can contribute to severe
environmental damage, and may lead to the
collapse of a society – Haiti is on the brink
o Deforestation led to sediment erosion during
hurricanes in 2008, which probably triggered 2010
earthquake
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Diamond’s Five-Point Framework –
1-4
• Diamond says that any combination of points
1-4 may or may not be present when a society
collapses
• He also says his fifth point is always involved
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Diamond’s Fifth Point
• A societies response to problems is critical, and will
determine whether or not the society survives
• An example is deforestation
 Diamond says Highland New Guinea, Japan, Tikopia, and
Tonga developed successful forest management practices,
and survived
 Easter Island, Mangareva, and Norse Greenland did not,
and failed
 Diamond suggests this may be an important reason for
problems in Haiti
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Response to Climate Change
• As we shall see, we are likely facing the
greatest climate change that has occurred while
our species has lived on earth
• How, or if, we respond will very likely have a
huge effect on the future of mankind
• We need to remember that doing nothing, often
called “business as usual”, is a response, and
will have extremely serious consequences
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