Weather, Climate, and Society

Spring 2012, Lecture 3

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Weather

• Day to day record Temperature Precipitation

• Time scale is short One week typical Two weeks maximum

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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

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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

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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

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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

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Climate

• Climate encompasses the statistics of meteorological elements in a given region over long periods of time

• Meteorological elements may include: 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 datao More precise ( tenths of a degree rather than a degree)o Better time resolutiono 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 Glacial iceo Stalagmiteso Lake and marine sediment cores, etc. o Tree ringso 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

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Geologic Materials

• Many geologic materials contain geochemical evidence of past climate conditions

• Examples are shown on the following slides

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Geologic Cores• Collecting sediment core samples

on Dillon Reservoir. (Photograph by Norman Spahr, U.S. Geological Survey.)

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• Core library, University of Kentucky

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

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• (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

Stalagmites• 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

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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

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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

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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

• 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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Born 10 September 1937

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

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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 

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 brinko 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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