Biology Reference
In-Depth Information
By analyzing natural records of climate in the form of tree rings and
sediment deposits, scientists have pieced together a chronicle of state cli-
mate extending back 10,000 years. Trees lay down a new ring of wood in
their trunks with each year; these rings are wider in wetter, warmer years.
Pollen trapped in mud can reveal which plant species grew there. Sedi-
ment cores can show how big and wide streams were in decades past, and
diatoms can indicate inundation by fresh versus salt water. Each of these
records provides a different snapshot of climate conditions. Overall, they
point to how lucky modern settlers in California have been—and how
much change may be in store.
About 10,000 years ago, the ice ages that had frozen much of North
America beneath glaciers began to thaw. A warmer, drier climate melted
polar ice and raised sea levels until the ocean could enter the Golden Gate.
Conditions warmed so much that by 6,000 years ago, bristlecone pines
and other mountaintop species had retreated to the highest peaks, and the
Years (A.D.)
0
200
400
600
800
1000
1200
1400
1600
1800
2000
*1
2
3
4
5
6
7
8
9
10
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14
Inferred Wet Periods
Inferred Dry Periods
Bay marsh vegetation
Mono Lake droughts
Flood event (size indicates
relative magnitude)
Tree ring evidence
Bay sediments
Timing unclear
Lake deposits
Tree ring evidence
Period of numerous
large floods
Period of three large floods
Unconformity
Figure 4. Extreme climate events in California over the last 2,000 years. *Numbers
refer to references provided in the original research paper. (Frances Malamud-
Roam, redrawn by UC Press)
