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 History:20 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 • 950-1300’s – Medieval Warm Spell • 1300’s – 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) • 950-1300’s – Medieval Warm Spell – Rise of “modern” European nation-states • 1300’s – 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 • Earth’s orbital variations