Global Climate Change

1
Global Climate Change

• A long term perspective

2
Global Warming

• CO2 levels in the atmosphere rising
• Average global temperature is rising
• Polar ice caps and mountain glaciers are
  shrinking
• Sea level is rising
• Deserts are expanding
• Weather is getting more severe

3
Is this normal?

• How can we tell if the present change in climate
  is normal or something produced by humans?
• Is the amount of present climate change normal or
  is it extreme?
• Is there any way to answer these questions?

4
Changing Perspectives

• Our perspective single human life.
• Expand to a few other generations.
• We need a longer time frame to evaluate global
  climate change.

5
Geologic Record

• Provides us with longer perspective
• Contains indirect evidence of climate
• Contains direct evidence of climate
• Gives us a history of global climate change on a
  scale of millions of years to billions of years.

6
Indirect Evidence

• Evidence for
• Aridity
• Warm Climate
• Cold Climate
• Recorded by specific types of rocks

7
Examples Desert sandstones
8
Examples Reef Limestones
9
Examples Glacial Features
10
Direct Evidence

• Ice Cores
• Sediment Cores
• Temperature Proxies

11
Ice Cores
12
Data from Ice Cores

• Direct Evidence for last 100,000 years
• Quantities of dust in each layer
• Related to wet vs. dry climate
• Air bubbles trapped in each layer
• Samples of ancient air
• Levels of CO2

13
Sediment Cores

• Deep Sea Drilling Project (DSDP)
• Ocean Drilling Project (ODP)
• Integrated Ocean Drilling Project (IODP)
• Coring in lakes and bogs

14
Data from Sediment Cores

• Quantity of mud vs. shelly material
• Relates to sea level, climate and weathering on
  land
• Temperature proxies
• From Chemical Signatures
• From Fossils

15
Temperature Proxies

• Stable Isotopes
• Not radioactive
• Proportions of stable isotopes are dependent on
  temperature
• Ratio of 18O to 16O
• Ratio of 13C to 12C
• Coiling in microfossils

16
What does theGeologic Record Tell Us?

• The normal climate of the past 1.0 billion
  years
• Warmer than present
• More uniform than present (less fluctuation)
• Past 20 million years have been highly variable
  and generally much colder

17
Climate History20 Ma to Present

• 20 Ma climate was somewhat moderate
• Similar to present
• 5 Ma coldest climate of past 65 million years
• 2 Ma Great Ice Ages begin
• At least 4 episodes of glacial advance and melt
  back
• 12,000 10,000 Modern Climate sets in

18
Recent Climate History

• 7000-6000 BP - Warm Peak
• 950-1300s Medieval Warm Spell
• 1300s Cool and Wet
• 1550 1850 Little Ice Age

19
Food For Thought

• How many of the great events of recorded human
  history have been directly influenced by climate?

20
Recent Climate History

• 7000-6000 BP - Warm Peak Great Ancient
  civilizations (e.g., Mesopotamia, Egypt)
• 950-1300s Medieval Warm Spell Rise of
  modern European nation-states
• 1300s Cool and Wet Bubonic Plague
• 1550 1850 Little Ice Age
• Washington crosses the Delaware
• Winter at Valley Forge

21
So, are we to blame?

• Paleoclimatic record reveals major shifts in
  climate through time
• Is it coincidence or causation that climate is
  warming as we come out of last ice age?
• Is it coincidence or causation that industrial
  revolution falls within this same time?

22
What factors cause changes in climate?

• Long term vs. short term changes
• Volcanic eruptions
• Earths orbital variations