How do we know about the temperature of the past? Are scientists just making this stuff up?
Goals:
Students will be able to define proxy data and provide specific examples of sources of proxy
data.
Students will understand that proxy data provides historical information about climate.
Hook
Minilesson
Practice
Debrief
Students pull out graphs from skeptic lesson, How do scientists know what the
temperature was in the year 1200?
Overview of different type of proxy data (see Randy’s link below for a short reading)
Define resolution and span
Explain stations and how to complete the charts with span, resolution, and brief
description.
Students rotate between stations and complete readings and interactive to complete a
chart. All students complete tree ring plus 1-2 other stations
Give students a scenario and have them choose a method to use and justify why it’s
appropriate in a small group
Resources:
http://eo.ucar.edu/staff/rrussell/climate/paleoclimate/paleoclimate_proxies.html (background on
proxies from Randy’s page)
http://www.outsourcesolutionsllc.com/science.html (purchase tree cookie)
Tree rings
Photos http://www.rmtrr.org/gallery.html
Activity http://www.windows2universe.org/earth/climate/dendrochronology_build_tree.html
http://www.windows2universe.org/earth/climate/treering_cores_align.html
Boring a tree ring core
Sawing a tree cross section
Tree rings
Background on Tree Rings
Trees contain some of nature's most accurate evidence of the past. Their growth layers, appearing
as rings in the cross section of the tree trunk, record evidence of floods, droughts, insect attacks,
lightning strikes, and even earthquakes.
Each year, a tree adds to its girth, the new growth being called a tree ring. Tree growth depends
upon local conditions such as water availability. Because the amount of water available to the
tree varies from year to year, scientists can use tree-ring patterns to reconstruct regional patterns
of drought and climatic change. This field of study, known as dendrochronology, was begun in
the early 1900s by an American astronomer named Andrew Ellicott Douglass.
A tree ring consists of two layers:

A light colored layer grows in the spring

A dark colored layer in late summer
During wet, cool years, most trees grow more than during hot, dry years and the rings are wider.
Drought or a severe winter can cause narrower rings. If the rings are a consistent width
throughout the tree, the climate was the same year after year. By counting the rings of a tree, we
can pretty accurately determine the age and health of the tree and the growing season of each
year.
Modern dendrochronologists seldom cut down a tree to analyze its rings. Instead, core samples
are extracted using a borer that's screwed into the tree and pulled out, bringing with it a strawsize sample of wood about 4 millimeters in diameter. The hole in the tree is then sealed to
prevent disease.
Computer analysis and other methods have allowed scientists to better understand certain largescale climatic changes that have occurred in past centuries. These methods also make highly
localized analyses possible. For example, archaeologists use tree rings to date timber from log
cabins and Native American pueblos by matching the rings from the cut timbers of homes to
rings in very old trees nearby. Matching these patterns can show the year a tree was cut, thus
revealing the age of a dwelling.
To investigate the extent, speed, and effects of historical climate changes locally and globally,
scientists rely on data collected from tree rings, ice cores, pollen samples, and the fossil record.
Computers are used to detect possible patterns and cycles from these sources. In
dendrochronology, large databases allow scientists to compare the ring records of many trees,
construct maps of former regional climates, and reveal when, where, and how quickly the
climates changed. These historical records are extremely valuable as we struggle to understand
the extent and nature of any possible future climate change.
Fire scars on a tree
Coral
Short overview video of proxy and corals
http://www.windows2universe.org/earth/climate/coral_proxy_climate_nsf.html
Lake Sediments
http://www.windows2universe.org/earth/climate/lake_sediment_proxy_climate_nsf.html
Pollen
Reading with bags of pollen and dirt, very abbreviated version of activity
Evidence found in the fossil record indicates that in the distant past, the earth's climate was very
different than it is today. There have also been substantial climatic fluctuations within the last
several centuries, too recently for the changes to be reflected in the fossil record. Since these
changes are important to understanding potential future climate change, scientists have
developed methods to study the climate of the recent past.
Although human-recorded weather records cover only the last few hundred years or so,
paleoclimatologists and paleobotanists have found ways of identifying the kinds of plants that
grew in a given area, from which they can infer the kind of climate that must have prevailed.
Because plants are generally distributed across the landscape based on temperature and
precipitation patterns, plant communities change as these climatic factors change. By knowing
the conditions that plants preferred, scientists can make general conclusions about the past
climate.
How do paleobotanists map plant distribution over time? One way is to study the pollen left in
lake sediments by wind-pollinated plants that once grew in the lake's vicinity. Sediment in the
bottom of lakes is ideal for determining pollen changes over time because it tends to be laid
down in annual layers (much like trees grow annual rings). Each layer traps the pollen that sank
into the lake or was carried into it by stream flow that year.
To look at the "pollen history" of a lake, scientists collect long cores of lake sediment, using
tubes approximately 5 centimeters (cm) in diameter. The cores can be 10 m long or longer,
depending upon the age of the lake and amount of sediment that's been deposited. The removed
core is sampled every 10 to 20 cm and washed in solutions of very strong, corrosive chemicals,
such as potassium hydroxide, hydrochloric acid, and hydrogen fluoride. This harsh process
removes the organic and mineral particles in the sample except for the pollen, which is composed
of some of the most chemically resistant organic compounds in nature. Microscope slides are
made of the remaining pollen and examined to count and identify the pollen grains.
Because every plant species has a distinctive pollen shape, botanists can identify from which
plant the pollen came. Through pollen analysis, botanists can estimate the composition of a lake
area by comparing the relative amount of pollen each species contributes to the whole pollen
sample. Carbon dating of the lake sediment cores gives an approximate age of the sample.
Scientists can infer the climate of the layer being studied by relating it to the current climatic
preferences of the same plants. For example, they can infer that a sediment layer with large
amounts of western red cedar pollen was deposited during a cool, wet climatic period, because
those are the current conditions most conducive to the growth of that species.
Why are scientists who study climate change interested in past climates? First, by examining the
pattern of plant changes over time, they can determine how long it took for plant species to
migrate into or out of a given area due to natural processes of climate change. This information
makes it easier to predict the speed with which plant communities might change in response to
future climate change. Second, by determining the kinds of plants that existed in an area when
the climate was warmer than at present, scientists can more accurately predict which plants will
be most likely to thrive if the climate warms again.
Packrat Middens (from windows to the universe
http://www.windows2universe.org/earth/climate/CDcourses_investigate_climate.html&edu=high)
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.
Several species of packrats live in the arid
deserts of western North America. Before
scientists began examining middens, little
was known about the past climates of desert
regions of North America, for other
paleoclimate proxies such as tree rings, fossil
pollen, ice and coral cores, and lake and
ocean sediments are either absent from these
regions or are too sparse to provide adequate
data. The peculiar middens turned out to be
gold mines of data for climate researchers!
A scientist examines a packrat midden.
Materials encased in middens are often
remarkably well-preserved. Scientists are
often able to sequence DNA from vegetation
in middens, providing them with
extraordinarily detailed insights to the
evolution of plant communities, which in turn are good indicators of climatic conditions. Other
astonishing artifacts have been discovered in middens. A midden from Utah contained a bone
from a camel that, though once widespread in North America, had gone extinct more than 12,000
years ago.
Credit:W.G. Spaulding and National Oceanic and Atmospheric
Administration Paleoclimatology Program/Department of Commerce
Packrats are not the only animals that produce middens. These peculiar structures are also
created by four families of rodents in South America (including a close relative of the
Chinchilla), a stick-nest rat in Australia, a hyrax (a distant relative of elephants) in Africa and the
Middle East, and a rock-dwelling vole in central Asia. Middens from these creatures are helping
scientists reconstruct the former extent of vegetation in arid regions around the globe, and to
infer the corresponding climate histories of those regions.
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.
Feces midden
Ice: it’s more than just frozen water
Time: 1-2 60 minute periods
Goals:
Students will make observations and gather data about simulated ice core samples.
Students will make inferences about climate change based on their data.
Students will analyze historical climate data (specifically CO2 levels) to identify trends, patterns,
and outliers.
Lesson Sequence:
Hook
Video show short version of Jim White video, show a graph
We are going to model what scientists do
MiniReview proxy data
lesson
Go over where, how, what we can learn
Read background in student text and students answer questions 1-2
Explain analysis procedure as a simulation for real data collection
Practice
Take measurements (depth of layer, observations of solids and color and mass if you have
a scale and can separate layers) skip volume and record the data. Answer questions 2
(discuss in group), 3 (written)
Procedure modification – put a layer of oil between ice layers to allow for easier separation
Mini
Read more of student text
Lesson
Explain how to graph,
Practice
Students graph and answer questions 5 as a class and look at graph 2 and answer question
1
Debrief
What did we learn about past climate? What is this simulating? How do you think scientists
use this data?
Resources:
NASA lesson plan
http://www.nsf.gov/news/special_reports/science_nation/icecores.jsp (show short
version as intro)
http://www.mos.org/soti/icecore/cores.html (ice core drilling photos)
http://nicl.usgs.gov/ant.htm (map of cores)
http://www.youtube.com/watch?v=eC1JtFQcvD0&feature=related (need to cut back from
6 min – show drilling
http://www.youtube.com/watch?v=OmGNaSHDWGU&feature=related (need to
condense)
http://www.windows2universe.org/earth/climate/ice_core_proxy_climate_nsf.html (video has
Jim White in it)