Transcript Slide 1 - Earth Portal Community

The Geologic Record of Climate Change:
The past informing the near future
From: The Day After Tomorrow, 20th Century Fox, 2004
http://www.ncdc.noaa.gov/paleo/paleo.html
Outline:
• Evidence for Natural 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
the duration of time over which they grew or were deposited
• The higher the resolution of the climate archive, the more important
it is to know the time frame maybe to within 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
we are not sure we have a continuous record due to the ravages
of weathering and erosion of rocks
• Consequently, old climate archives give us general climate
knowledge at best
Cold Environments:
Pleistocene Glaciation
Pleistocene (15 kyr) glacial till
Pre-Cambrian (>1 billion yrs)
glacial tillite
Humid Environments:
Pennsylvanian Coal Forest
Tree ‘bark’
300 million yr. old tree
Arid Environments: Wind
Arid Environments: Water
Sahara Desert
Triassic Navaho SS – Zion NP
Present-day and Permian (255 mya)
salt deposits
Warm, marine environments:
Pleistocene coral rubble
Great Barrier Reef
Permian Reef, Texas
Ancient Climate Records
Looking for the Climate “Tape recorder”:
•The concept of a climate archive:
•A process that records climate directly or indirectly
•Useful for time scales and time periods greater
than human instrumental recording (i.e., before 1800)
• How can climate be recorded in deep time?
• What kinds of processes might give us a record
of climate?
• How long of a record might we obtain?
• The basis for all this is UNIFORMITARIANISM:
The Present is the Key to the Past
The last millennial temperature trend:
Avg. 1961-1990 = 0.0
Climate Proxies
Historical
Record
Instr.
Record
Climate Proxies with High Resolution records:
•Ice Cores
Gas bubbles trapped in ice
Result of the isotopic “fractionation” process
on marine sediments and ice
Terrestrial Climate indicators
• Lacustrine (Lake) levels
Present Lake
Glacial Shore
(16,000 yr BP)
200 million year old lake seds
POLLEN
Historical Climate Proxies with High Resolution records:
• Dendochronology – Tree Rings
Complacent
Sensitive
Cross-dating of trees
Recent (Instrumental) Climate Change
Grinnell Glacier, Glacier National Park, Montana
1938
1981
1998
2005
ARCTIC ICE SHEET MELTING
1953-2007
If CO2 is rising what should happen to global temperature?
Hadley Centre/UEA-CRU data