How do we know about the climate 150,000 years ago?

Are scientists making stuff up?
Are they
using time
Climate data of the past
Actual Measurements
Humans have been
recording climate using
instruments for only the
past ~100-200 years
Instruments to record
temperature, wind, precipitation,
Climate data of the past
Historical Records
•Old journals describing natural disasters
•Agricultural records, for example when grapes were harvested
•Old records of when different plants were in bloom
•Voyage records
Bradley, R.S., 1991. Pre-instrumental
climate: how has climate varied
during the past 500 years?
Garcia et al. Manila Galleons Voyage Records
Climate data of the past
Paleoclimatologists use paleoclimate proxies.
proxy: An indicator of past climate. A proxy (meaning
“substitute”) is an indirect measure of climate, as
opposed to direct measures such as reading
temperature from a thermometer.
Just as Sherlock Holmes might infer the height,
weight, and other telltale features of a suspect from
a series of footprints, paleoclimatologists infer the
climatic conditions of the past from tree rings, ice
cores, layers of ocean sediments, fossils, and
similar proxy evidence.
Introduction to proxy data video
Span and Resolution
Span = how far into the past the proxy information goes
Resolution = how specific the climate information is in
terms of years
A higher resolution ca n give you information about a
specific year.
A lower resolution will show long-term changes that
occur over many years.
Span and Resolution of Proxy Sources
Time Limits of Various Proxy Data
(years past)
Where does proxy sampling occur?
location of proxy data
Ice Cores
Jim White: Stable Isotope Lab @ CU
Tree Rings
Canadian model
Hadley model
Combining all of the proxy data
Proxy data source
Tree Rings
2 Corals
3 Packrat Middens
4 Lake and Ocean
5 Pollen in lake
a sediments
5 Fossils
6 Ice Cores
Description of
how it is
Where is it
How far
does it
Station 1 – Dendochronology (Tree Rings)
1. Read the background information on tree rings. (see printed text)
2. Then click on the link below, You be the Dendochronologist and practice
making different width rings and matching exising data. Follow the
instructions on the page.
3. Complete your chart.
You be the dendochronologist
Station 2 - Corals
1. Read the text and watch the video. Click on coral video to link to the page.
coral video
2. Watch a short video (no sound) to see how the coral cores are collected.
3. Complete your chart
coral core collection (no sound)
How we measure past sea level from
Acropora palmata coral
Acropora palmata is a coral that
only grows in water that is less
than 5 meters deep.
Scientist drilling for coral
Therefore if it is found in a
location, you can infer that that
location was once under 5 meters
or less of water.
Stations 3 - Packrat Middens
Packrat Middens
Packrat Middens
Packrats, as their name implies, constantly collect all kinds of materials
from their surroundings. Their collections, called "middens", provide
clues to the past climates of the region. Packrat middens are clumps of
vegetation, insects, remains of vertebrates, and other materials
cemented together by crystallized packrat urine (referred to as amberat).
These rock-hard deposits can be more than 20,000 years old.
Packrat making a midden
Source: San Diego Natural History Museum
A sample of packrat midden
from Red Creek (RC2) that
dates to 3320 B.P. Needles of
lodgepole pine were recovered
from this midden found in the
lower basin.
A scientist examines a packrat midden.
Credit:W.G. Spaulding and National Oceanic and Atmospheric
Administration Paleoclimatology Program/Department of
Station 4 –Lake and Ocean Sediments
1. Watch the video and read the text. Click on the lake sediment proxy
link to view the video.
Lake Sediment proxy data video and text
more information and pictures on lake sediments
2. Complete your chart.
Collecting a lake sediment core
Station 5
Lake Sediments and Pollen
Station 6 – Ice Cores
1. Which proxy data would be appropriate for determining climate 1.5
million years ago?
2. Which proxy data would be appropriate for determining the climate
around Hawaii?
3. If you were wondering if there was an ocean in Colorado, which type
of proxy data would be appropriate?
4. Looking at your graphs, which type of proxies might have been used
and why?
5. In your journal, explain to a skeptic: “How scientists know about the
climate of the past.”
Ice: It’s more than just frozen water
What Can Ice Cores Tell us about
Past Climate?
Jim White short version video of ice
Earth’s climate changes. Although there is debate over what
causes this change, scientists agree that Earth’s climate has
changed and continues to change over time. One way to learn
about these changes is through the study of glacial ice cores. Ice
cores create a layered historical record of the climate over time.
Scientists drill deeper into older layers of ice; sometimes to a
depth of over 3,500 meters (2.2 miles).
By performing physical and chemical tests on ice cores,
scientists can create a snapshot of the Earth at single points in
time. Atmospheric gases, from hundreds to thousands of years
ago, are trapped as small bubbles within the ice.
Measurements of gases, including carbon dioxide, paint a
picture of the atmosphere at the time the gases were trapped.
How are they collected?
Figure 1. Ice Core Sampling. Image credit: Reto Stöckii, NASA GSFC
An ice core section
Where are they collected?
map of drilling sites
Side view showing dust & ash layers
(from drought years and volcanoes)
Melting a core sample
to release the trapped gases

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