Global Climate Change

All answers should be in BLUE font. Answers not in blue will not be graded.

In this lab you will:
• Examine the basic driving forces behind Earth’s climate system and how the release of greenhouse gases by human activity is disrupting the system. You will also explore some of the expected consequences of climate change and proposed strategies for mitigating the impacts.

Background Reading and Needed Supplies
Prior to doing this exercise you should read Chapter 16, Global Climate Change in the textbook.

Part I – Earth’s Climate System
As described more thoroughly in Chapter 16 of the text, Earth’s climate system is very complex and changes over geologic time. However, the system does not change on its own, and what’s most worrisome today is that it is changing at an unprecedented rate. Climate scientists have learned that the system responds to so-called climate drivers or forcings. They have identified the major drivers, and now have a pretty good understanding of how and why the climate system changes. Moreover, the vast majority of climate scientists have concluded that the release of greenhouse gases by human activity is the primary driving force behind the rapid changes currently being observed. In this section we will examine some of the key aspects of Earth’s climate system and why it is undergoing such rapid change.

1) Figure 8.1 shows how solar radiation strikes Earth’s surface and is converted into heat energy. Explain how greenhouse gases trap some of this energy and help warm the planet.

Figure 8.1. Conceptual model illustrating how solar radiation strikes Earth’s surface and is converted into heat energy. Greenhouse gases in turn trap some of this heat and warm the atmosphere. (rei22967_16_07)

2) Describe how the global average surface temperature (land and water) should adjust when the concentration of greenhouse gases change over time.

In addition to the greenhouse effect and small changes in solar output, scientists have discovered that variations in Earth’s orbit also force the climate system to change. As described in the textbook, there are the basic orbital changes that affect the intensity and timing of Earth’s seasons: 1) shape of the orbit (eccentricity), 2) tilt of the axis, and 3) wobble in the axis (precession). As illustrated in Figure 8.2a, these three parameters operate over different time scales. This results in periods where all three parameters act together and push the climate system towards a warmer state, and at other times they act together and push the system towards a cooler state. Scientists have shown that these so-called Milankovitch Cycles are what trigger the glacial and interglacial cycles found in Earth’s climate history (Figure 8.2b) for the past several million years.

(A) (B)
Figure 8.2. Plot (A) shows how variations in Earth’s orbit periodically coincide and act together to push the climate system towards either a warmer or cooler state. Graph in (B) showing glacial cycles in Greenland’s temperature and carbon dioxide record over the past 450,000 years. (A: rei22967_16_09, B: rei22967_16_22)

3) Based on the Greenland’s temperature and CO2 record shown in Figure 8.2b, describe the relationship between the two variables. In other words what happens to CO2 when temperatures are warmer, and what happens when temperatures are cooler?

4) Describe how global temperature changes affect plant growth, and how this in turn would affect atmospheric CO2 concentrations.

You may have noticed in the previous questions that when global temperatures change, some parts of the climate system respond in ways that reinforces or amplifies the initial change. Scientists refer to such processes as climate feedbacks. A positive feedback is one that reinforces or amplifies the initial change, such as releasing CO2 from a warming ocean, which then leads to additional warming. In contrast, a negative feedback is one that reduces or minimizes the initial change. An example here would be when temperatures rise, more CO2 is removed from the atmosphere by plants, which acts to reduce the warming.

One of the most powerful climate feedbacks is related to changes in the amount of snow and ice covering Earth’s oceans and land surface. As illustrated in Figure 8.3, when electromagnetic radiation from the Sun strikes the Earth, some of it is reflected back into space and the rest is absorbed and converted into heat energy. Notice in the figure that in areas covered by light material (snow and ice), most of the radiation is reflected, hence, very little solar heating takes place. In contrast, very little radiation is reflected in areas with dark surfaces (vegetated land and open water), so most of it is converted into heat.

Figure 8.3. Illustration showing how the amount of reflected versus absorbed solar radiation varies depending whether the surface is light colored (snow and ice) or dark (water and land). (rei22967_16_11)

5) Assuming that global temperatures continue to rise, describe how this will affect the relative amounts of snow and ice covered areas versus that covered by vegetated landscapes and open water.

6) Based on Figure 8.3, describe how the loss of snow and ice cover will affect the amount of solar of heating on the planet as a whole. Explain how this change would then affect the remaining amount of snow and ice cover. Include the role of climate feedbacks in your answer.

Recall that variations in Earth’s orbit over time (Milankovitch Cycles) create small increases and decreases in Earth’s heat balance. These small temperature changes are then amplified by positive feedbacks, which eventually send the planet into either a glacial (cold) or interglacial (warm) period. Finally, negative feedbacks act to keep the warming or cooling trend from spiraling out of control, thereby allowing the planet to reach a new state of semi-equilibrium in either a warmer or cooler state. The fact that Earth’s climate system moves between cooler (glacial) and warmer (interglacial) states of semi-equilibrium is well documented in the 800,000 year Antarctic ice-core record shown in Figure 8.4. For example, notice how temperatures (blue) pretty much stay within the dashed lines that represent the system’s upper (interglacial) and lower (glacial) operating limits. Likewise, both methane (green) and carbon dioxide (red) tend to stay within their own set of upper and lower operating limits.
Figure 8.4. A deep ice core from Antarctica revels variations in temperature (blue), methane (green) and carbon dioxide (red) over the past 800,000 years. Dashed lines represent the upper (interglacial) and lower (glacial) operating limit of each parameter. (rei22967_16_26)

7a) Look at the temperature (blue) curve in Figure 8.4 and, based on the discussion above, describe what initially causes the climate system to move from a glacial state (lower dashed line) and towards a warmer interglacial state (upper dashed line)?

b) After the climate system is nudged out of the glacial equilibrium and begins to warm, explain what keeps pushing the climate system towards a warmer state.

c) What ultimately keeps the system from continuing to warm beyond the upper (interglacial) operating limit of the system?

8a) Based on the Antarctic record shown Figure 8.4, what have been the lower and upper concentration limits of carbon dioxide (CO2) in the atmosphere for the past 800,000 years?

b) Similarly, what have been the lower and upper concentration limits of methane (CH4) over the past 800,000 years?

c) What were atmospheric CO2 and CH4 concentrations in 2015?

9) Clearly, the atmospheric concentrations of CO2 and CH4 are currently way above their upper operating ranges over the past 800,000 years. Based on what you learned so far in this exercise, describe how the climate system will most likely respond to this large and rather sudden input of greenhouse gases.

Some people claim that the modern rise in global temperatures shown in Figure 8.5a is caused by changes in the output of solar energy from the Sun. However, scientists who study the Sun have demonstrated that the variation in solar output cannot account for the modern temperature rise. Moreover, other scientists have shown that the rise can easily be accounted for by the increased concentration of greenhouse gases shown in 8.5b. Note that along with water vapor, the major greenhouse gases are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).

(A) (B)
Figure 8.5. Graph (A) shows the modern rise in average global surface temperatures, and (B) shows the sudden and dramatic rise in greenhouse gas concentrations since the industrial revolution. (A: rei22967_16_02, B: rei22967_16_03)

10). Notice in Figure 8.5b how the spike in greenhouse gas concentrations began around 1800, which coincides with the beginning of the Industrial Revolution. List 3 human-related factors that have contributed to this sudden increase in greenhouse gas concentrations.

11) Explain how deforestation and the accompanying feedback mechanisms contribute to the changes in greenhouse gas concentrations.

Part II – Consequences of Global Warming
As described in the textbook, humans are facing many serious consequences related to global warming and climate change. As shown in Figure 8.6, global warming is causing the planet’s climate system to shift to a higher energy state, resulting in more hot weather events and fewer cold events. In addition to temperature changes, scientists are documenting changes in precipitation patterns, an increase in the frequency and intensity of storms and droughts, changes in the timing of the seasons, shifting of biomes towards the poles, and accelerated sea level rise. In this section we will examine just a few of the expected consequences associated with this shift to a higher energy state.

Figure 8.6. Climate is the statistical variation in daily weather events, where the number of days of cool weather roughly equals the number of warm days. Global warming is causing a shift in climates worldwide, resulting in more hot weather events and record highs. (rei22967_16_24)

12a) Explain the basic reason why global warming is causing heavy precipitation events to occur more frequently.

b) Describe how this leads to increased flooding.

c) Who is at risk for increased flooding?

d) Think back to your flood hazards lab and the reasons why people live in areas that have a potential for flooding. Select one of your lines of reasoning and explain whether or not that reason is enough to keep people living in these areas even though the risk for flooding is increasing.

Figure 8.7. Map showing the current locations of major deserts (gray) and vulnerability of different areas to undergo desertification. As global temperatures increase, existing deserts are expected to expand. (rei22967_16_31)

13a) If heavy rains occur more frequently, explain how it’s possible for droughts to occur more often and with greater intensity. Use Figure 8.7 to help you with your answer.

b) What will happen to the aquifers in places that experience prolonged droughts?

c) What will people do for water in these regions? Is this solution sustainable?

When the average global temperature changes, so too does the volume of glacial ice being stored on the planet’s landmasses. During cool (glacial) periods, sea level falls as additional water is removed from the oceans and stored as glacial ice. Sea level then rises when the climate enters a warm (interglacial) period and the ice begins melt. Of course, whenever sea level changes, the position of the shoreline changes. Shorelines naturally advance (shift seaward) when sea level falls, then retreat (shift landward) as sea level rises. There is nothing really special then about the position of today’s shoreline. The problem is that humans have grown accustomed to today’s shoreline.

Although the climate system has been relatively stable for the past 10,000 years, sea level has continued to slowly rise as the climate moved from an ice age to the current interglacial period. For example, the amount of sea level rise from 1900 to 2000 was only 0.6 feet (0.2 m). One of the major concerns today about global warming is that sea-level rise is accelerating because of the rapid melting of glacial ice and thermal expansion of the oceans. If all of the remaining ice were to melt, sea level would rise an additional 260 feet (80 m). Currently, the worst-case scenario predicted by climate scientists is a 33-foot (10 m) rise over the course of a few centuries. Were this to occur, major population centers and massive amounts of infrastructure around the world would be inundated, creating a human catastrophe of unprecedented portions. In order to get a better sense of the potential problems associated with accelerated sea level rise, we will examine the projected shoreline changes for southern Florida shown in Figure 8.9. Note that the changes here represent the worst-case scenario of a 33-foot (10 m) rise in sea level over a several hundred year period.
(A) (B)
Figure 8.9. Relief map (A) of the current shoreline in southern Florida, and (B) the shoreline associated with a 33-foot (10 m) sea-level rise. (Courtesy of NASA). (rei22967_16_11)

14) Assuming sea level will rise slow enough to allow people and businesses to relocate inland in an orderly manner, list and explain at least 2 problems such a move would entail.

15) How will coastal hazards change with rising sea level?

Part III – Mitigating Climate Change
If the world could somehow immediately stop all greenhouse gas emissions, what we’ve already released into the atmosphere will continue to warm the planet for decades, or even longer. However, as illustrated in Figure 8.10, what we can do is to minimize the consequences of additional global warming by dramatically reducing our emissions as quickly as possible. In particular, we desperately need to prevent the climate system from reaching the point where positive feedbacks cause the warming to accelerate beyond our control.

(A) (B)
Figure 8.10. Future CO2 emission scenarios (A) based on an emission reduction strategy that makes use of individual reduction wedges or triangles. Projected global warming (B) under continued emission trend (red) and reduced emission (B) strategy. (A: rei22967_16_40, B: rei22967_16_19)

16) What could we do to not reduce emissions, stabilize emissions, and reduce emissions? For each strategy, also list what it will take for the human population to implement that action.

17) Since the rise in greenhouse gas concentrations has been shown to be the primary cause of global warming, describe 3 ways that correspond with the factors you listed in question 10 in which humans could reduce the concentrations of these gasses in the atmosphere.

18) If climate change does not slow down, what do you think will happen to life on Earth?

Sample Solution