LAB 11: CLIMATE CHANGE
Past, Present, and Future In this lab you will learn about the changes to Earth’s climate in the past, and the current and future global warming of the planet. You will then investigate the impacts of past, present and future climate change on glacial and coastal environments.
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LAB 11: CLIMATE CHANGE Past, Present, and Future
The Earth’s climate has been changing throughout its 4.6 billion-year history. These climatic shifts can be gradual or dramatic. Our planet has experienced numerous “Ice Ages”, when glaciers have advanced and large portions of North America have been covered in ice and global sea level dropped. Conversely, our planet has also undergone periods of warming, where global temperatures rise, ice melts, and sea level rises. Our planet is currently in a period of unprecedented global warming: global temperatures are rising dramatically, glaciers and ice caps are rapidly retreating and melting, and sea level is rising.
In this lab you will explore how Earth’s climate has changed in the past, and how current climate changes are affecting us presently and in the future.
PALEOCLIMATE Geologists have studied Earth’s past climate, or paleoclimate, and learned that temperature and sea level have changed dramatically throughout Earth’s history. We now have a good record of Earth’s paleoclimate from several sources, including tree rings, the rock record, fossils, and ice cores. Tree rings can give us a short-term record (past several thousand years) of past temperatures. Geologists can also piece together the paleoclimate from the rock record and fossils. For example, the occurrence of marine limestones at A- Mountain in Las Cruces tells us that, in spite of the arid climate and high elevation today, this part of New Mexico was once under an ocean. Animals live in distinct climates on Earth, so their fossils are good indicators of paleoclimate as well. For example, the fossils of wooly mammoths are commonly found in Michigan, indicating that the climate in Michigan was much cooler in the past. The chemistry of ice cores from thick ice sheets, like those in Greenland and Antarctica, provide detailed paleoclimate records. The ice in the cores is composed of many layers of snow and ice trapped over hundreds of thousands of years. It is these ice core records that have provided us with the most detailed look at temperature changes in Earth’s past (for example, the Antarctic ice cores are ~ 3 km long and record Earth’s temperature over the past ~800,000 years).
Using these datasets, geologists have pieced together Earth’s paleoclimate. We now know that Earth has been both much warmer and also much cooler in the past than it is today. The Earth has clearly experienced natural fluctuations in temperature over time. For example, the Earth’s climate periodically cools significantly, producing times of glaciations or “Ice Ages” that have occurred every 40,000-100,000 years during the past two million years. These Ice Ages were periods of global cooling, when glaciers advanced to lower latitudes. During the last Ice Age, which peaked ~21,000 years ago, an ice sheet extended from Greenland through Canada and into what is now the northern U.S. This was also a time of greater rainfall in the western U.S. and large lakes were present in now-arid regions, for example in Utah (Lake Bonneville) and New Mexico (Lake Otero, now the location of White Sands sand dunes!).
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Figure 1. Variations in global temperatures over the past 800,000 years. The large drops in temperature every ~100,000 years correspond with Ice Ages, which are separated by warmer “inter- glacial” periods. (from NASA)
Although much of Earth’s paleoclimate can be explained by natural fluctuations, our current climate is changing at an alarming rate. Overall, Earth’s climate had been cooling for the past ~50 million years, but in the past 100 years or so, global temperatures have increased dramatically (Fig. 2). This temperature increase is happening rapidly, and is occurring at the same time as concentrations of CO2 and methane (greenhouse gases) in the atmosphere are increasing at rapid rates. These increases are linked, and likely caused by human activities (increased burning of fossil fuels, increases in agriculture, deforestation, etc.). This global warming is an issue facing not only scientists, who are trying to model the future climate and searching for solutions to minimize the rise in global temperatures, but an issue that will impact all of us in our lifetimes, as we deal with the changes (e.g., changes in weather patterns, extreme weather, sea level rise) that come with it.
Figure 2. Variations in global temperatures over the past 1500 years. Note the rapid increases in global temperature in the last ~100 years. (from NASA)
IMPACTS OF CLIMATE CHANGE The impacts of a changing Earth climate are broad. Increases in global temperatures cause ice to melt and thus sea level to rise. These changes in turn affect precipitation patterns; some regions may get more rain, others may experience drought. Extreme weather events
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occur with greater frequency. All of these effects of a warming planet will clearly affect the human population of our planet – rising sea levels will displace low-lying coastal communities, farmers will need to adapt to changing temperatures and amounts of rainfall, and communities will be impacted by increased extreme weather events (hurricanes, tornadoes, heavy rainfall and subsequent landslides, etc.). We will explore just two of the areas affected by changing climate – glaciers and sea level – in the past, present, and future.
Glaciers Glaciers are flowing bodies of ice that form from the accumulation and compaction of snow. They range in size from relatively small ice masses in the valleys of mountain ranges (Fig. 3) to massive ice sheets like those currently covering Greenland and Antarctica. Glaciers can be found everywhere from the poles to the equator – as long as temperatures are cold enough to maintain ice year round (high latitudes, high elevation), glaciers can form.
Figure 3. The retreating Schoolroom glacier, Grand Teton National Park (photo: E. Johnson) Although glaciers may seem like large, immobile features, glaciers are actually in motion. Snow falls, accumulates and compacts on the upper parts of the glacier (zone of accumulation), creating new ice (Fig. 4). Below snowline (equilibrium line), the glacier is melting (zone of wastage). This accumulation at high elevation and melting at low elevation results in the glacier flowing down slope. As glaciers flow, they transport sediment that is incorporated at the base of the glacier and sediment that has fallen on top of the glacier. This sediment is deposited in thick ridges on the sides of the glacier forming lateral moraines, and at the toe of the glacier in a terminal moraine (Fig. 3).
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Figure 4. Cross-section of a glacier. The equilibrium line (also snowline) divides the zone of accumulation from the zone of wastage (or melting).
Although glacial ice always flows downhill, glaciers as a whole can either advance or retreat. Glaciers advance when the amount of accumulation (snowfall) is greater than the amount of wastage (melting). In this case, the length of the glacier increases and the toe of the glacier advances. Glaciers retreat if the amount of wastage is greater than the amount of accumulation, and the toe of the glacier will move uphill and the length of the glacier decreases. If the amount of accumulation and wastage are equal, the size of the glacier will be constant. You can imagine then how increasing global temperatures can affect glaciers: higher temperatures shift the equilibrium line (snowline) to higher elevation and thus cause glaciers to retreat.
Glaciers also provide us with a look into the Earth’s past climate through their deposits. Geologists can map out the moraines left behind by glaciers and estimate how much glaciers have retreated or advanced in the past. What’s more, we can use this information to estimate past temperatures. The equilibrium line is a snow line that is located about halfway between the top of a glacier and the toe of a glacier (Fig. 4). The location of this line can tell us the elevation of the freezing point (0°C, or 32°F) on any given glacier. By using the elevation of the terminal moraine (at the toe/base) of a retreated glacier and the elevation of the top of the glacier we can estimate where the equilibrium line was in the past. Temperature varies with elevation by approximately 2°C/300 m (so, if you were hiking up in the mountains, you would expect the temperature to drop by about 2°C for every 300 meters of elevation you climb).
Sea Level Sea level fluctuates with the changes in Earth’s climate. In times when the climate has been cooler sea level was lower. For example, during the last glacial maximum 21,000 years ago sea level was ~120 m lower than it is today. When the climate cools, the amount of ice on Earth increases and sea level drops because water becomes locked up as ice on land. When the climate warms, ice on land (glaciers) melts, and sea level rises. Warming global temperatures have a double impact on sea level: not only does more ice melt, but the ocean waters warm and expand (warm water takes up a larger volume than cold water), increasing sea level even further.
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The impacts of sea level rise and fall on coastlines depend on the slope of the shoreline at the coast. As illustrated in Figure 5, you can see that if sea level were to rise one meter (the upper-estimate of sea level rise by 2100), coastlines with steep slopes or sea cliffs will not be impacted as dramatically as those with low slopes.
Figure 5. The effect of a rise in sea level of 1 m on a coastline with a steep slope (left) and with a low slope (right). With a low slope, the new shoreline will move farther inland.
NAME:_____________________________________
ASSIGNMENT PART ONE: PALEOCLIMATE AND GLACIATION IN THE TETON RANGE, WYOMING
1. Use the map in the lab manual (see the color version in the online version of the lab) to look at the extent of the Teton Glacier. a) Find the Teton Glacier on the topo map (also consult with color images
provided in the intro presentation). What is the bottom elevation of the glacier?
b) What is upper elevation of the glacier?
c) What is the elevation of the equilibrium line (refer to Figure 4 and the text on p. 159)?
2. During the last Ice Age the Teton Glacier occupied the valley labeled “Glacier Gulch” on the map. a) Find the ancient terminal moraine for the Teton Glacier, which marks the toe of
the glacier in the past. Describe its location on the map. (HINT: the moraine sediment is commonly more heavily forested). What was the bottom elevation of the glacier?
b) Assuming that the ancient Teton Glacier extended up to the top of the ridge above the modern Teton Glacier, what was the approximate elevation of the top of the glacier?
c) What was the elevation of the equilibrium line?
3. The location of the equilibrium line in the past compared to today can allow us to estimate how temperature has changed over time. a) What is the elevation difference between the two equilibrium lines (past and
present) in meters? (remember that 1 ft = 0.3048 m)
b) Remembering that the equilibrium line is the height of average annual freezing temperature (0°C), what is the temperature change (in °C) associated with this change in the equilibrium line?
110°45’W110°46’W110°47’W110°48’W
43° 44’N
0 1 2 3 40.5 km Contour interval = 80 ft
Topographic map of the Grand Teton area (portions of the USGS Grand Teton and Moose 7.5′ quadrangles)
Contour interval = 20 ft
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NAME:_________________________________________
ASSIGNMENT PART TWO: MODERN AND FUTURE GLACIAL RETREAT Answer the following questions using the Google Earth images of the Coleman Glacier on Mt. Baker, a volcano in the Cascade range of Washington. These images appear on the following page of the lab pdf file provided on Canvas.
4. The Google Earth images provided show a satellite image of the Coleman Glacier
taken in August of 1993 and in July of 2013. Measured on the image, the glacier has retreated approximately 2.9 cm. The 300 m scale bar also measured on the image is 3.7 cm long. Using these values, about how far did the glacier retreat from 1993-2013? (show your work and provide your answer in meters)
5. What is the rate (distance over time) of retreat of the Coleman glacier over this time period? (show your work)
6. The remaining Coleman glacier is about 4200 m long. If the rate you calculated above was to continue unchanged, in how many years might the Coleman glacier disappear? (show your work)
August, 1993
July, 2013
2001000 300 m
2001000 300 m
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NAME:_________________________________________
ASSIGNMENT PART THREE: CHANGES IN SEA LEVEL The following questions relate to changes in sea level in the past and future around Florida.
7. Below is a graph showing monthly average sea level observed in Key West, Florida
from 1913 through 2014. The line on the graph below shows the approximate average sea level rise over this time period.
8. Using the line drawn above, calculate the rate of sea level rise in millimeter s
per year over this time period, in other words, the slope of your line (recall that slope, in this case, is change in sea level divided by the time over which that change occurred). Show your work.
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NAME:_________________________________________
9. If the rate you calculated for the 100 years shown in the graph continues, what is
the expected sea level rise for southern Florida 100 years from now?
10. Scientists have estimated that, globally, sea level could rise by as much as one meter by 2100. a) How does this compare to what you calculated in #9?
b) What process could cause the rate of sea level rise to increase in the future?
11. The map on the following page in the lab manual shows a portion of southeastern Florida. See the page after that in the online lab manual for possible answers.
a) Sea level is expected to rise by as much as 1 m by 2100. (NOTE: the contour lines are shaded, and in centimeters where visible). Look at the lines drawn on the map, and give the letter of line that best represents the position of the shoreline if the sea level were to rise by 1 m.
b) How would this rise in sea level affect local infrastructure?
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HOMESTEAD FLORIDA CITY
80°10’W80°14’W80°18’W80°22’W80°26’W
25° 32’N
25° 28’N
25° 24’N
25° 20’N
25° 16’N
25° 12’N
25° 8’N
0 5 102.5 km
Elevation meters
0 0 – 0.4 0.4 – 0.8 0.8 – 1.2 1.2 – 1.6 >1.6
HOMESTEAD
FLORIDA CITY
80°10’W80°14’W80°18’W80°22’W80°26’W
25 °3
2′ N
25 °2
8′ N
25 °2
4′ N
25 °2
0′ N
25 °1
6′ N
25 °1
2′ N
25 °8
‘N
0 5 102.5 km
Elevation meters
0
0 – 0.4
0.4 – 0.8
0.8 – 1.2
1.2 – 1.6
>1.6
A
B
C D
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NAME:_________________________________________
12. Use the contour map of Florida and the ocean floor on the next page to answer the
questions below. See the page after that in the online lab to see the shoreline choices for both (a) and (c). a) Based on the maps on the following pages, which of the lines (A through E) best
shows the outline of the land during the last Ice Age when global sea level was about 130 meters lower than today?
b) Which side of the continental shelf offshore of modern Florida has a steeper slope, and how would this have affected prehistoric people living near the shoreline during the transition from the last Ice Age to modern sea level?
c) Now, imagine that global warming continues un-checked into the future. If ALL of the ice on Earth were to melt, sea level could rise by ~80 meters! If glacial melting continues into the future until sea level rises by 30 m, where would the shoreline be? Using the maps on the following pages of the online lab handout, which of the lines A through E best shows the position of the Florida shoreline if sea level rose 30 m above the modern level?
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