Global Climate Change A long term perspective

Global Warming CO 2 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

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?

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

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.

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

Examples: Desert sandstones

Examples: Reef Limestones

Examples: Glacial Features

Direct Evidence Ice Cores Sediment Cores Temperature Proxies

Ice Cores

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 CO 2

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

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

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

What does the Geologic 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 2 Ma – Great Ice Ages begin –At least 4 episodes of glacial advance and melt back 12,000 – 10,000 Modern Climate sets in

Recent Climate History BP - Warm Peak ’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 BP - Warm Peak – Great Ancient civilizations (e.g., Mesopotamia, Egypt) ’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