Fossils, Paleoclimateand Global Climate Change

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 (transgression)

• Deserts are expanding

• Weather is getting more severe (?)

Is this normal?

• How can we tell if the present change in climate is normal or not?

• Is the amount/rate of present climate change normal or is it extreme?

• Are humans responsible?

• Is there any way to answer these questions?

Geologic Record

• Provides us with long-term 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.

• Fossils are a key source of this information

Indirect Evidence• Evidence for

– Aridity

– Warm Climate

– Cold Climate

• Recorded by specific types of rocks

Direct Evidence: Ice Cores

• 100,000 years of continuous record

• Older than 100,000 is too distorted by plastic flow and mixing

Data from Ice Cores

• 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

Sediment Cores

• Deep Sea Drilling Project (DSDP)

• Ocean Drilling Project (ODP)

• Integrated Ocean Drilling Program (IODP)

• Coring in lakes and bogs

• DSDP, ODP and IODP cores can extend back to Early to Middle Jurassic (approx. 180-200 Ma)

Data from Sediment Cores

• Quantity of mud vs. shelly material– Relates to sea level, climate and weathering on

land

• Temperature proxies– Chemical signatures– Coiling in microfossils– Chemical signatures from fossil shells

Temperature Proxies: Stable Isotopes

• Stable Isotopes are NOT radioactive

• Proportions of stable isotopes are dependent on temperature

• Ratio of 18O to 16O

• Ratio of 13C to 12C

Stable Isotopes• 18O is heavier than 16O• Therefore it is harder to evaporate water with

18O than “normal” water• 18O is enriched in oceans – especially when

climate is cold• 18O is depleted in atmosphere when climate is

cold• Therefore ice is depleted in 18O• When climate is warmer, there is more 18O in

atmosphere and therefore in ice• Carbon isotopes follow similar trends

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

Climate History:20 Ma to Present

• 20 Ma – climate was somewhat moderate– Similar to present

• 5 Ma – coldest climate of past 65 million years

Pleistocene Epoch:the Great Ice Ages

• 2.0 Ma to 10,000 years ago – Pleistocene Epoch

• Four (or more) distinct episodes expansion and melting of ice sheets (continental glaciers)

• 12,000 – 10,000 Modern Climate sets in

Recent Climate History

• 7000-6000 BP - Warm Peak

• 950-1300’s – Medieval Warm Spell

• 1300’s – Cool and Wet

• 1550 – 1850 – “Little Ice Age”

Food For Thought

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

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

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?

What factors cause changes in climate?

• Long term vs. short term changes

• Volcanic eruptions

• Earth’s orbital variations

Why did the climate change so drastically and repeadedly?

• Climate change and variations in Earth’s orbit

• Eccentricity: elliptical to nearly circular cycles

• Obliquity: cyclic changes in tilt of axis

• Precession: cyclic change in”wobble” of the axis

• Variations affect amount and distribution of solar energy received by Earth

• Influence climate