Past and Present Climate Change and Variability

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Past and Present ClimateChange and Variability

• Paleoclimatology
• Past Climates
• Recent Climate Change and Variability
• Chapters 12.1 12.2 and 14.1

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Paleoclimatology
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• Definition
• The study of climate before the period of
  instrumental records

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Paleoclimatology
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• Why study paleoclimatology?
• See how climates have changed in the past
• Test hypotheses on the causes of climate
  variation
• See how human actions might affect future climates

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Paleoclimatology
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• Sources of paleoclimate data
• Historical Records
• Tree rings
• Lake sediments
• Pollen (Palynology)
• Ice cores
• Ocean Cores

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Paleoclimatology
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• The climate of the past can be determined from
  these paleoclimate data sources
• Temperature and Precipitation can be inferred
  from these sources for the past hundreds,
  thousands, or millions of years

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• Temperature record of
• the past 2 million years
• Based on oxygen-isotope
• ratios in deep-sea cores

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Glacial Periods for the Past 500 Thousand Years
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Generalized Extent of a Glacial Maximum
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Northern Hemisphere Temperature Anomaly Trends
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Past Temperature Trends
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• Secondary Optimum
• 1000 1200 AD
• A short period of warming before the Little Ice
  Age
• The Little Ice Age
• 1430 1850 AD
• An extended cool period

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The Little Ice Age
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The Little Ice Age
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• Global temperatures were 1º - 2º cooler than the
  temperatures of the twentieth century from about
  1430 to 1850 AD
• General Impacts
• Reduced agricultural yields increased prices
• Malnutrition, epidemics, population loss

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Recent Temperature Trends
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Climate Change and Variability
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• Climate variation
• Natural variation in the climate system around
  the mean
• Climate change
• A change in the mean of the climate
• Largely attributed to human activity that has
  altered the composition of the global atmosphere
• In addition to natural climate variation

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Recent Temperature Trends
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Climate Variability
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• Sources of climate variability
• ENSO
• NAO
• PNA
• Volcanoes
• Solar output (sunspot cycles)

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Climate Change
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• Sources of climate change
• Changes in the Earths orbital parameters
• Changes in atmospheric composition, such as
  greenhouse gases
• Changes in land configuration and surface
  characteristics
• Changes in solar luminosity

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Recent Temperature Trends
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Future Climates
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• What will the future climate look like?
• Warmer?
• Cooler?
• Wetter?
• Drier?

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