From: The Day After Tomorrow, 20 th Century Fox, 2004 The Geologic Record of Climate Change: The past informing the near future The past informing the near future

Outline: Evidence for Natural Climate Change Evidence for Natural Climate Change Evidence for Anthropogenic Climate Change Evidence for Anthropogenic Climate Change

Climate Change over Geologic Time

How do we know climate varied over Geologic Time?

The Importance of TIME: How accurate is the climate data? All the climate indicators we have discussed so far depend on knowing All the climate indicators we have discussed so far depend on knowing the duration of time over which they grew or were deposited The higher the resolution of the climate archive, the more important The higher the resolution of the climate archive, the more important it is to know the time frame maybe to within years it is to know the time frame maybe to within years As the climate archives get older (i.e., deposited millions of years As the climate archives get older (i.e., deposited millions of years ago or more), we not only have trouble dating the archive but ago or more), we not only have trouble dating the archive but we are not sure we have a continuous record due to the ravages we are not sure we have a continuous record due to the ravages of weathering and erosion of rocks of weathering and erosion of rocks Consequently, old climate archives give us general climate Consequently, old climate archives give us general climate knowledge at best knowledge at best

Cold Environments: Pre-Cambrian (>1 billion yrs) glacial tillite Pleistocene (15 kyr) glacial till Pleistocene Glaciation

Humid Environments: Pennsylvanian Coal Forest Tree ‘bark’ 300 million yr. old tree Soil surface Tree

Arid Environments: Wind Triassic Navaho SS – Zion NP Sahara Desert Arid Environments: Water Present-day and Permian (255 mya) salt deposits

Warm, marine environments: Great Barrier Reef Permian Reef, Texas Pleistocene coral rubble

Ancient Climate Records

Looking for the Climate “Tape recorder”: The concept of a climate archive:The concept of a climate archive: A process that records climate directly or indirectlyA process that records climate directly or indirectly Useful for time scales and time periods greaterUseful for time scales and time periods greater than human instrumental recording (i.e., before 1800) How can climate be recorded in deep time? How can climate be recorded in deep time? What kinds of processes might give us a record What kinds of processes might give us a record of climate? How long of a record might we obtain? How long of a record might we obtain? The basis for all this is UNIFORMITARIANISM: The basis for all this is UNIFORMITARIANISM: The Present is the Key to the Past The Present is the Key to the Past

The last millennial temperature trend: Climate Proxies Historical Record Instr. Record Avg = 0.0

Climate Proxies with High Resolution records: Ice CoresIce Cores Gas bubbles trapped in ice

Result of the isotopic “fractionation” process on marine sediments and ice

Terrestrial Climate indicators Lacustrine (Lake) levels Lacustrine (Lake) levels Glacial Shore (16,000 yr BP) Present Lake 200 million year old lake seds

POLLEN

Historical Climate Proxies with High Resolution records: Dendochronology – Tree Rings Dendochronology – Tree RingsComplacent Sensitive

Cross-dating of trees

Recent (Instrumental) Climate Change Grinnell Glacier, Glacier National Park, Montana

ARCTIC ICE SHEET MELTING ARCTIC ICE SHEET MELTING

If CO 2 is rising what should happen to global temperature?

Hadley Centre/UEA-CRU data