Climate is an average of the long-term weather

| March 14, 2016

6

Climate Change
Bradley Deline

6.1 Introduction
Climate is an average of the long-term weather patterns across a geographic area, which is a complicated metric controlled by factors within the lithosphere, atmosphere, cryosphere, hydrosphere, biosphere, and anthrosphere as well as factors
beyond our own planet. It is helpful to separate out humans from other life (anthrosphere verses biosphere) for several reasons, primarily because many of our activities are unique amongst life (industrialization) and it is helpful in understanding our
role in climate change. Therefore, the science examining past, current, and future
climate is extremely complex and interdisciplinary. You may not think of climate
as a geological field of study, but the history of climate is recorded within rocks, the
current climate is altered by geologic events, and future climate will be influenced by
our use of geological resources such as fossil fuels. In addition to the complex nature
of this subject, it is also one, if not the most, important scientific fields of study both
in terms of understanding the dynamics and implications of future climate change
as well as attempting to combat or mitigate the potential effects.
Though the basic science behind climate and climate change has been well
studied to a point of near consensus within the scientific community, there is still
significant debate amongst the broader population. This is likely related to many
factors beyond science including economics, politics, the portrayal of the science
by the media, and the overall public’s scientific literacy. Gaining a better understanding of this issue is difficult given the enormous wealth of information and
disparity in scientific literacy. This lab will explore this issue by examining climate
data as well as how we, as scientists or scientific minded citizens, make interpretations and conclusions regarding data, how it is presented, and how it relates to our
understanding of the world around us.

6.1.1 Learning Outcomes
After completing this chapter, you should be able to:
• Describe the climate system and how different variables are related
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• Discuss how ancient climate patterns are reconstructed
• Plot, interpret, and explain the patterns in climate proxy data focusing
on the sea ice extent in the North and South Poles
• Describe how heat is transported across the earth and how this can
relate to local climate
• Describe the information needed to make conclusions regarding
scientific patterns and how climate models should be constructed

6.1.2 Key Terms
• Albedo

• Ice Extent

• Climate Proxies

• Negative Feedback

• Climate System

• Ocean Gyres

• Greenhouse Gases

• Positive Feedback

6.2 The Climate System
As was previously mentioned, climate is the long-term weather pattern across a
region. It is important to emphasize the long-term portion of the definition to establish that climate is different from weather. Weather is the local and short-term patterns in temperature, humidity, precipitation, atmospheric pressure, wind, and other meteorological variables. As you well know, weather fluctuates throughout the
day, week, month, and year such that it is difficult to see any trends beyond the random noise in the system. If you take a long-term view of weather we can begin to see
patterns across time and geography that help to better understand and identify the
factors that influence the climate system. The climate system is the interconnected network of variables that influence the earth’s
climate, which includes components from the lithosphere, atmosphere, hydrosphere, cryosphere, biosphere, anthrosphere, and solar system.
The heat that feeds this system comes from two
primary sources. First, there is heat radiating from
the Earth itself, which is coming from the decay
of radioactive material and residual heat from the
formation of the earth. This heat is not distributed
equally, with more heat escaping in areas where Figure 6.1 | The Earth’s shape influences the angle at which the sun’s
the crust is thinner, such as divergent boundaries. rays hit the surface from perpendicular at the equator to parallel at
More significantly, the earth receives heat from the poles. This creates large climate
solar radiation. Again, this heat is not distributed differences across the Earth.
Author: Bradley Deline
equally across the earth’s surface and the amount Source: Original Work
of energy received is related to the angle at which License: CC BY-SA 3.0

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the solar radiation hits the surface of the earth (Figure 6.1). If the solar radiation
hits perpendicular to the surface more heat is absorbed than if it hits at an oblique
angle, which is why the tropics are warmer than the poles.
The material on the Earth’s surface is also important in that materials react
differently to solar radiation. Some materials, normally dark in color, absorb and
reradiate heat, most of which is retained at the surface of the planet. You are likely familiar with this if you have ever walked barefoot on dark concrete or asphalt
in the summer. Other materials, that are shiny or light in color, reflect the solar
radiation off the Earth’s surface. Materials such as snow or ice are particularly
effective at reflecting solar radiation. This is the reason Arctic explorers must use
eye protection to avoid snow blindness. The proportion of solar radiation that is
reflected off the Earth’s surface is called albedo, which can vary depending on the
type of ground cover. For instance the Earth’s albedo is higher when it is covered
with large expanses of glacial ice and thus the amount of sunlight absorbed and the
temperature measured are lower.
Once heat is reradiated off of the Earth’s surface it travels up into the atmosphere. Certain gases in Earth’s atmosphere, called greenhouse gases, allow sunlight to pass but absorb terrestrial energy and radiate it in all directions including
back to the surface of the Earth. These gases, such as water vapor, carbon dioxide,
and methane represent a tiny, though important fraction of the material in the atmosphere. Different greenhouse gases vary both in how effectively they absorb and
reradiate energy and their relative proportions in the atmosphere, such that a higher
concentration of potent greenhouse gases can retain more thermal energy within the
atmosphere. The rest of the reflected and radiated energy escapes from the atmosphere and dissipates into space.
Several factors can influence the simplified version of the climate system described above. The amount of radiation produced from the sun varies over time. In
addition, the shape of our orbit around the sun varies over time from more circular
to more elliptical because of the gravitational influences from other planets in our
solar system. The angle at which solar radiation hits the planets’ surface is influenced by the tilt and wobble of the Earth’s axis. The distribution of water, ice, snow,
vegetation, and other materials on the Earth’s surface control the Earth’s albedo and
can change over time. The proportion of greenhouse gases can change dramatically
depending on the rate of plate motion as well as the amount of volcanism, photosynthesis, weathering of rocks, burning of fossil fuels, and many other factors (to
examine trends on climate and carbon dioxide levels see Figure 6.5 later in the lab).
The efficiency of the transportation of heat across the surface of the Earth also influences climate. Heat is transferred across the surface of the planet by wind,
ocean currents, and storms. Therefore, the position of the continents as well as air
and ocean currents affect climate and can change over time. The components in our
atmosphere are also important, including water vapor and aerosols (dust). Water
vapor in the atmosphere is a greenhouse gas, can reflect incoming solar radiation,
and is the source of precipitation. Aerosols can come from the Earth’s surface, ash
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from volcanoes, and the burning of
fossil fuels and can alter climate by
reflecting incoming solar radiation
before it reaches the Earth’s surface.
There are numerous additional factors that also have some level of effect
on the climate system.
At this point you should be able
to recognize the complexity of the climate system based on the number of
variables and how those variables can
change over time. It is also important
to recognize that all of these variables
are connected. For instance, if a volcano erupts it adds some thermal energy to the climate system; it produces aerosols that block solar radiation
from hitting the Earth’s surface, and
produces greenhouse gases that retain heat. Notice that these factors do
Figure 6.2 | A simple diagram showing the relationship benot all influence climate in a consis- tween two variables with either positive or negative feedback
following a positive (A) or negative (B) initial change.
tent way. The change of one variable Author: Bradley Deline
as the result of another is called feed- Source: Original Work
back, which can be either positive or License: CC BY-SA 3.0
negative (Figure 6.2). Positive feedback reinforces the initial change no matter
the direction of that change. For instance, if the Earth warms, ice melts and reduces
the albedo, which causes even more warming. This can also occur in the opposite
direction, if the Earth cools, ice forms and increase the albedo, which causes more
cooling. Negative feedback counteracts the initial change no matter the direction of the initial change. For instance, if the Earth warms, more area becomes arid
resulting in an increase in the amount of dust in the atmosphere, which reflects
solar radiation causing cooling. Again the opposite works, if the Earth cools, less
area is arid resulting in a decrease in the amount of dust in the atmosphere, which
causes warming. Therefore, an understanding of the climate system requires an
identification of all of the important climate variables, how they are related to each
other, the speed at which they can change, and the magnitude and direction of
change of each feedback loop. The ideal way to gain a better understanding of the
climate system is to study it through geologic history.

6.3 Climate Proxies and The Climate Record
The first method most students think about when we talk about recording climate is using a thermometer to directly measure temperature. There are actually a

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few problems reconstructing climate patterns this way, including that a thermometer gives a very local signal and more importantly, thermometers are a relatively
recent invention. Given that direct observations do not give us the long-term trends
needed to establish climate change or patterns, we must look at a natural recorder
of climate called a climate proxy. As climate changes it affects the deposition of
sedimentary rock, rock chemistry, and fossil organisms that scientists can detect in
order to reconstruct ancient climate patterns, in a field called paleoclimatology. An
individual climate proxy may not give a clear signal of global climate for a couple
of reasons. First, proxies show a history of the area in which they were formed, not
of an entire region. Second, an individual proxy, which may have a long or a short
record, can record the short-term variability of weather events. And third, most
climate proxies are influenced by multiple factors. For instance, the thickness of
tree rings (dendrochronology) is a wonderful proxy for temperature. Trees grow
more in warmer years (producing thicker rings) and less in colder years (producing thinner rings). However, a tree could also grow slowly because of a drought or
because of an infestation of pests even if it was a warm year.
If all of the individual proxies show local patterns, with some degree of weather
related noise, and possibly influenced by other factors, how do we then reconstruct
long-term global temperature records? The answer lies in increasing the size of the
dataset. If temperature is the most important variable influencing the proxies, and
we combine hundreds to thousands of individual proxy records, an overarching
pattern emerges from the noise. Again, an individual proxy record may be contrary
to the overall trend, but that is expected since a local region can have a cold winter
in the midst of an overall hot year for the planet. To illustrate this consider the following: say we want to reconstruct overall economic patterns over the past few hundred years in the United States of America. We could examine lots of proxies for
economic growth, such as employment, the stock market, individual wealth, or
rates of home ownership to name a few. If we only looked at one of these proxies we
likely would not get a clear picture of change. Also, if we only looked at Macon,
Georgia, for example, we would be unlikely to see a trend that mimics the entire country. For instance if a new factory
opened outside of Macon, GA that would
be a huge economic benefit for the city,
but not for the country overall. Again, the
more data we have, whether it is for economics, or climate, or any other complex
system, the clearer the signal becomes
over the local and random noise.
One of the most commonly used cliFigure 6.3 | Short segment of an ice core that
mate proxy is the measurement of oxy- records ancient climate patterns.
gen isotopes. As you may remember Author: Ludovic Brucker, NASA
from chapter one, isotopes are atoms of Source: Wikimedia Commons
License: Public Domain

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the same element that differ in their weights because of differences in the number
of neutrons in the nucleus of the atom. Multiple isotopes of oxygen are stable,
meaning they do not radioactively decay over time. Oxygen has two stable isotopes
that occur in a constant ratio on Earth. However, certain minerals (like calcite or
ice) prefer one of the isotopes over the other within their crystal structure (a slightly larger or smaller atom fits better). This preference results in a ratio of oxygen
isotopes that is different from the ratio found in other materials; this difference is
called fractionation. The amount of fractionation in oxygen isotopes is temperature dependent, such that the mineral calcite has a different ratio of oxygen isotopes if it was formed in near freezing versus warm water temperatures. Using
oxygen isotopes we can get climate records from many different sources, including
coral, clams and other mollusks, the skeletons of single-celled organisms, and ice
cores to name a few. Ice cores (as shown in
Figure 6.3) can contain a wealth of climate
data in addition to temperature data from
oxygen isotopes, such as air bubbles that record the levels of greenhouse gases, concentrations of windblown aerosols, and ash from
volcanic eruptions.
Other proxies include the extent of glacial sediment, sea level curves, pollen (palynology), and fossils. For instance, climatologists have used several features within
fossil plants to reconstruct climate, largely
because these organisms are sensitive to climate. These proxies include the thickness of
tree rings, the shape of the leaves (toothier
leaves are more common in colder climates),
and the density of pores on leaf surfaces
(more pores are needed with lower concentrations of carbon dioxide, which is necessary for photosynthesis).
As was mentioned before, by combining
hundreds to thousands of individual climate Figure 6.4 | Distribution of individual climate
records we can start to gain insight into over- proxies used in the construction of Figure 5.
all climate trends. For instance, the Intergov- Image from the National Ocean and Atmospheric
Administration.
ernmental Panel on Climate Change (IPCC) Author: NOAA
and the National Oceanic and Atmospheric Source: NOAA
Administration (NOAA) regularly compile License: Public Domain
multiple types of proxy records from across the world (Figure 6.4) to reconstruct climate patterns (Figure 6.5). The accuracy of the climate records very much depends
on the time frame being considered, with more certainty in the patterns of the recent
past (Cenozoic) and less the further back in geologic time we are examining.
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Figure 6.5 | Climate reconstruction over the last 1300 years using multiple climate proxies (different colored
lines) from “Climate change 2007: the physical science basis”; Contribution of Working Group I to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change Jansen, E. J. Overpeck, K. R. Briffa, J.
C. Duplessy, F. Joss, V. Masson-Delmotte, D. Olago, B. Otto-Bliesner, W. R. Peltier, S. Rahmstorf, R. Ramesh, D.
Raynaud, D. Rind, O. Solomina, R. Villalba, and D. Zhang.
Author: NOAA
Source: Wikimedia Commons
License: Public Domain

The climate proxy we will focus on for this lab is the extent of sea ice coverage
on the North and South Polar ice sheets. This is an easy proxy to assess from satellite images and is measured as the size of the ice sheet in million square kilometers. This proxy isn’t a perfect indicator of global climate change, but it is easy to
understand that a warming of the Earth is likely to cause a decrease in the amount
of ice at the poles and thus a decrease in the ice extent, while a cooling event will
cause an increase in ice production. Ice extent is simply the amount of geographic
area covered by a glacier as measured from satellites.
There is debate surrounding the interpretation of individual proxies and the
resulting climate records, which largely stems from the economic and political aspects of climate change. This current lab was constructed following a discussion
with a student regarding the information presented in several climate articles. The
discussion focused on how scientific data is presented to the public and how we
should make conclusions based on presented data. In considering information
that we are presented with it is important to consider 1) the source of the data, 2)
how the data was collected, 3) how the data is presented, and, most importantly 4)
what are the reasonable conclusions you should make from the data independent
of the opinions expressed alongside of the data.

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6.4 Lab Exercise
As with Chapter 4, you will be expected to input your answers to this lab in several ways. There will be a couple of multiple-choice questions, but for the majority
of the lab you will write your answers in the provided text box. This allows you to
show your work in the questions requiring calculations as well as allowing you to
answer open-ended questions thoroughly with multiple sentences. You will be expected to use correct grammar and complete sentences in your answers.

Materials
All of the data provided in the lab comes from the National Snow and Ice Data Center (NSIDC), housed at the University of Colorado. The data presented in
this lab can be freely downloaded from them at nsidc.org. The original discussion
was focused on a widely circulated though unattributed article entitled “Antarctic
Sea Ice for March 2010 Significantly Greater Than 1980” published in April 2010
(climatechangehoax.com). For the dataset presented in this article as well as the
following datasets, do the following before answering each set of questions: graph
the data, connect the data points to better see the pattern through time, estimate
the best fit line, and calculate the slope of the best fit line. Make sure to think about
the data before you estimate the line of best fit so that your line falls within the data
and is consistent with the trend in the data. An example of this process is shown
in Figure 6.6.

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Figure 6.6 | Steps needed to analyze the ice extent data to visualize patterns: place a line of best fit,
and calculate the slope of that line.
Author: Bradley Deline
Source: Original Work
License: CC BY-SA 3.0

Part A – Original Data
First, we want to take a closer look at the data presented in the original article
(“Antarctic Sea Ice for March 2010 Significantly Greater Than 1980”) and interpret the
data. Feel free to read the article, but it isn’t needed to complete the assignment or
understand the patterns it is presenting. The data, which is included to the left of
the graph below, is the extent of Antarctic sea ice in millions of square kilometers
as measured in March of 1980 and 2010. This data is accurate and is consistent
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with data that can be downloaded from NSIDC. To do this, follow the instructions
in Figure 6.6. In this case, steps two and three are the same and you can easily calculate slope using the original data.

1. Based exclusively on the data provided and your graph, what conclusion would
you make regarding climate change?
a. Sea ice is expanding, which indicates an increase in temperature
b. Sea ice is expanding, which indicates a decrease in temperature
c. Sea ice is contracting, which indicates an increase in temperature
d. Sea ice is contracting, which indicates a decrease in temperature
2. What is slope of the line of best fit for this data?
a. 0.008 million square kilometers per year
b. 0.05 million square kilometers per year
c. -0.05 million square kilometers per year
d. 0.017 million square kilometers per year
e. -0.17 million square kilometer per year
f. 0.033 million square kilometer per year

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3. Even though the above data is accurate, give and explain two reasons why this
dataset might lead you to an incorrect conclusion regarding global climate change.

Part B – South Pole Sea Ice Extent
Below is an expanded dataset showing Antarctic sea ice (Figure 6.7) extent measured during
March 1980 through 2012 again downloaded
from NSIDC. Only the even numbered years are
presented, but the addition of odd years does not
alter the trend in the data. Following the instructions in Figure 6.6, graph the data, draw a line of
best fit, and calculate the slope of the line.
Figure 6.7 | Map of Antarctica showing
the extent of the polar ice cap and the
extent of the floating ice shelves.
Author: USGS
Source: Wikimedia Commons
License: Public Domain

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4. What is the slope of the line of best fit you estimated for this data set? Make
sure to show your work.

5. What conclusion about climate change could you make from this dataset? How
does your result for the extended dataset compare to the results from the data
presented in the article (Part A)?

Part C – North Pole Sea Ice Extent
Next, we will examine the ice extent patterns of the northern Arctic polar ice
sheet that is located around Greenland (Figure 6.8). The ice extent data is from
March 1980 through 2012, for even numbered years, again downloaded from
NSIDC. Following the instructions in Figure 6.6, graph the data, draw a line of best
fit, and calculate the slope of the line.

Figure 6.8 | Map of Greenland showing the extent of
the polar ice cap.
Author: Eric Gaba
Source: Wikimedia Commons
License: CC BY-SA 3.0

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6. What is the slope of the line of best fit you estimated for this data set? Make
sure to show your work.

7. What conclusion on climate change could you make from this dataset? How
does your result for the North Pole compare to that of the South Pole (Part B)?

6.5 Heat Transport and Ocean Currents
As was mentioned earlier in the lab, the tropics are warmer than the poles because of differences in the angle at which solar radiation impacts the Earth (Figure
6.1). Very little solar radiation reaches higher latitude areas because the solar radiation comes in almost parallel to the Earth’s surface. Therefore, most of the thermal energy at higher latitudes comes from the movement of heat from the tropics.
Heat is transported across the Earth’s surface through wind currents, storms, and
ocean currents. In particular, large circular ocean currents, called gyres, appear
to have a significant impact on the geographic distribution of heat on Earth and
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tive in melting polar ice in that they melt the sea ice from below. In addition, an
examination of ocean current patterns will assist in explaining the patterns of sea
ice extent you graphed earlier as the earth is warming (Part B and C).

6.6 Lab Exercise
Materials
A visualization of the ocean currents can be seen by downloading the file
“ocean_currents.kml” either from your course’s website or directly from the Science on a Sphere page from NOAA (sos.noaa.gov/kml/). Once you download the
file you…
Tutorials for thi

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