EM SC 470
Applied Sustainability in Contemporary Culture

Climate Change

Climate change is widely considered the single most important sustainability issue today, if not the most pressing. If the climate continues to change, the impacts will likely be catastrophic and on a global scale. Also, climate change will likely impact all of the other sectors of sustainability and society. Because of this, I want to make sure you understand a lot of the key issues surrounding what we know and don't know, and so have included the entire EM SC 240N Climate Change lesson page. If you can answer all of the following questions in detail, then you are in pretty good shape for this part of the lesson. 

Learning Objectives Self-Check

Read through the following statements/questions. You should be able to answer all of these after reading through the content on this page. I suggest writing or typing out your answers, but if nothing else, say them out loud to yourself.

 Briefly describe what the following terms mean: greenhouse effect, enhanced greenhouse effect, greenhouse gas, anthropogenic, anthropogenic climate change.
 How do greenhouse gases keep the earth's surface warmer than it would be without them?
 Between carbon dioxide and methane, which is a more potent greenhouse gas, and which one are scientists more concerned about?
 Provide 2 reasons why we know that humans have caused an increase in global carbon dioxide levels.
 Describe one specific way that climate change is an equity issue.
 Is there 100% scientific consensus that climate change is being caused by humans?
 What is the "precautionary principle," and how does it relate to climate change?

First, a few important terms:

  • Greenhouse effect: the term used to describe the phenomenon whereby infrared heat warms the lower atmosphere of the earth or another planet due to the gaseous content of the atmosphere.
  • Enhanced greenhouse effect: This occurs when the magnitude of the greenhouse effect is enhanced by human activity, due to the emission of greenhouse gases at an unnaturally high level.
  • Greenhouse gas: a gas that absorbs infrared radiation and contributes to the greenhouse effect.
  • Anthropogenic: caused by humans.
  • Anthropogenic climate change: the component of climate change that is believed to be caused by humans.

The following article from the U.S. National Aeronautics and Space Administration (NASA) explains a lot of the basics regarding the terms listed above.

Fact 1: The Greenhouse Effect is Settled Science

The greenhouse effect is a universally accepted natural phenomenon, and carbon dioxide (CO2) is one of the primary greenhouse gases. Without it, life on earth would not be possible. The video below from NASA does the best job of succinctly explaining the greenhouse effect of any video I've found. It is not the most high-tech video out there, but don't let that distract you from the content. (For those of you who have been around long enough to remember a teacher popping a tape into a VCR player connected to one of those big CRT televisions, this may spark some memories.)

The Greenhouse Effect
Click Here for Transcript of The Greenhouse Effect Video

Earth's greenhouse effect greatly affects climate. See if you can describe how carbon dioxide and water vapor cause Earth's greenhouse effect. Also, see if you can describe how the greenhouse effect maintains the surface temperature of Earth.

Scientists have long known that the presence of an atmosphere keeps the surface of the planet warmer than it would be without an atmosphere. In fact, without an atmosphere, the surface of the earth would be about 30 degrees Celsius cooler than it is now. In order to understand why, we need to consider the surface of the earth and its atmosphere separately. Because there is a radiative equilibrium we know that the planet emits enough longwave radiation into space to equal the solar radiation absorbed by it. However, most of the longwave radiation that is emitted by the planet into space is emitted by the atmosphere rather than the surface of the earth beneath it. Although the surface of the earth does emit longwave radiation, only about 10 percent of this radiation passes through the atmosphere and escapes into space. The rest is absorbed by clouds and by greenhouse gases in the atmosphere.

There are many greenhouse gases but the most abundant greenhouse gases are water vapor and carbon dioxide. Shortwave radiation from the Sun passes through greenhouse gases, but longwave radiation is absorbed by them. Greenhouse gases absorb longwave radiation that is emitted by the surface of the earth. Subsequently, they re-emit the energy as longwave radiation in all directions. About half of the re-emitted longwave radiation does escape into space and contributes to the planet's radiative equilibrium. About half of the longwave radiation emitted by the gases is directed back toward the surface of the earth. As a result, a continual exchange of longwave radiation takes place between the surface of the earth and the atmosphere above it. The longwave radiation contained in this exchange causes the warming effect known as the greenhouse effect.

This phenomenon is known as the greenhouse effect because, like the glass in a greenhouse, the atmosphere traps some of the energy beneath it. The greenhouse effect produces a warmer climate on earth than would be possible without an atmosphere.

In summary, water vapor and carbon dioxide allow solar energy to penetrate Earth's atmosphere but prevent much of the longwave radiation emitted by the surface of the earth from escaping to space. This trapping of longwave energy is called the greenhouse effect and enhances the surface temperature of the earth.

Credit: NASA

In a nutshell:

  • Greenhouse gases (GHGs) allow shortwave radiation to pass through them, but absorb longwave radiation and re-radiate it in all directions after they absorb it. This is simply a physical property of certain gases. Nature just doing its thing.
  • Sunlight is mostly shortwave radiation, so passes through the GHGs on its way toward the earth's surface.
  • If the shortwave radiation is reflected on or near the earth's surface (e.g., by clouds, water, physical objects), it passes back through the GHGs, because it is still shortwave. It goes back out to space.
  • If the shortwave radiation is absorbed on or near the earth's surface (e.g., by your skin, water, soil, other surfaces) then it is radiated as longwave radiation. (This is radiant/electromagnetic heat transfer that was mentioned in Lesson 1, by the way!)
  • If this longwave radiation hits a GHG molecule on its way out, it is absorbed and re-radiated in all directions.
  • Some of that longwave radiation (about 50%) heads back towards the earth's surface. This results in warming that would not occur if the GHGs were not in the atmosphere.

The following gases contribute to the greenhouse effect: water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs). There are a lot of details about each, but the main focus of anthropocentric climate change is carbon dioxide and methane because they play the largest role in the climate impact that most scientists believe humans are having.

Note that methane is considered approximately 30 times as powerful as carbon dioxide in terms of causing increased warming (over a 100 year period). Methane is the primary component of natural gas and is what gives natural gas its energy. If natural gas is burned, it releases about half as much CO2 as if you burn an equivalent amount of coal. But if natural gas leaks or is otherwise emitted, it is about 30 times more potent than carbon dioxide. Despite this, carbon dioxide reduction is the main focus because it is far and away the biggest contributor to anthropogenic greenhouse gas emissions impact.

Fact 2: Carbon Dioxide Levels are Increasing Due to Human Activity

There are a few fundamental things to know in regards to the carbon dioxide content of the atmosphere.

  • First, the amount of CO2 in the atmosphere is measured in parts per million (ppm). A concentration of 1 ppm means that there is one unit of mass of fluid for every million units of mass of the enveloping fluid. The current concentration of carbon dioxide is a little more than 400 ppm. (FYI, this means that if you took 1 kg of air, there would be about 400/1,000,000 kg, which is 0.0004 kg or 0.4 g of CO2 in that kg of air.)
  • Second, the atmosphere is considered the same everywhere you go on earth. Localized variations occur, but the current CO2 concentration s considered to be effectively the same no matter where you are on earth.

We have been directly measuring the atmospheric concentration of CO2 since 1958 in the Mauna Loa Observatory in Hawaii, and have seen it increase steadily since then (see Figure 3.1 below). This is known as the Keeling curve and is named after Andrew Keeling, who initiated the measurements.

Atmospheric concentration of carbon dioxide since 1958, as measured at the Mauna Loa Observatory in Hawaii.
Figure 3.2: Direct measurements of atmospheric CO2 levels have been made since 1958. They have been rising steadily since then. The trend is undeniable.
Click for a text description
The chart illustrates the fact that since 1958, atmospheric levels of CO2 have risen steadily. In 1958, there was about 315 ppm, and by the summer of 2018 has risen to nearly 410 ppm.
Credit: Public domain image (NASA)

We also know with a very high level of certainty the concentration of the ancient atmosphere through time, as well through proxy measures such as ice core samples from ancient ice (click here for some links to explanations of how this is done by clicking on the CO2 Past at the top of the page). The current levels of CO2 are almost certainly unprecedented in the past 800,000 years (credit: National Academy of Sciences). The chart below depicts the carbon dioxide levels in the atmosphere for the past 400,000 years.

Atmospheric concentration of carbon dioxide for the past 400,000 years.
Figure 3.3: Atmospheric concentration of carbon dioxide for the past 400,000 years.
Click for a text description
The chart illustrates the fact that for 650,000 years atmospheric levels of CO2 fluctuated up and down but never rose above 300 ppm until 1950. Levels have continued to rise since then. The current CO2 level depicted on the chart is nearly 400 ppm (as of July 2013).
Credit: Public domain image (NASA)

It is an established fact that the burning of fossil fuels releases carbon dioxide and that the concentration of carbon dioxide has been increasing rapidly since around the beginning of the Industrial Revolution in the late 1700s. The Industrial Revolution is characterized by the increased use of fossil fuels - first coal, then oil, then natural gas. All of these non-renewable energy sources release CO2 when burned, and aside from minor natural occurrences like volcanic eruptions, are what has primarily caused the increased carbon dioxide concentration over the past 200+ years.

In short, energy is the primary culprit in anthropogenic greenhouse gas emissions. In fact, according to the International Energy Agency, two-thirds of global anthropogenic greenhouse gas emissions are due to energy use and production (Credit: IEA, "Energy and Climate Change," World Energy Outlook 2015). This boils down to the fact that we are emitting carbon dioxide and other greenhouse gases at rates faster than can naturally be absorbed. This causes an imbalance, and thus the concentration increases.

Mythbusting: The Global Carbon Cycle

It is not unusual to hear something like the following as a reason to be skeptical of anthropogenic climate change: "The earth naturally emits WAY more CO2 than humans do. The emissions are so relatively small that they cannot have an impact on CO2 concentrations, never mind climate change."

The earth does, in fact, emit significantly more CO2 than humans do! The image below is from the Intergovernmental Panel on Climate Change's (IPCC) most recent report, called the Fifth Assessment Report or simply AR5. This is an illustration of the global carbon cycle. Carbon, like most other elements, is constantly moving around the earth, e.g., being emitted and absorbed by oceans, being taken up by plants, being released by decaying plants, being released by volcanoes, etc. The carbon cycle illustrates this process. (Don't worry about analyzing this image if you don't want to - it's pretty dense, and you do not need to know any of the numbers.)

This image shows an illustration of the various sources and sinks of carbon dioxide. The natural emissions are significantly higher than the anthropogenic emissions.
Figure 3.4: The global carbon cycle, by major source. Note that anything red indicates an anthropogenic source. See page 7 of this report for a resizable image. (Link to a text version of Figure 3.3 that opens in a new tab.)
Credit: Intergovernmental Panel on Climate Change Fifth Assessment Report, Figure 6.1.

This is a pretty busy image, so I'll summarize it for you:

  • Humans directly cause about 9 billion tonnes (Gt) of carbon to enter the atmosphere each year.
  • Natural emissions are on the order of 170 Gt per year.

Hmm, okay, so there are way more natural than anthropogenic emissions. So why care so much about the measly 9 billion anthropogenic tonnes? As it turns out, if there were no anthropogenic emissions, the carbon cycle would likely even out, or perhaps even cause a reduction in carbon in the atmosphere. There are many natural processes that absorb carbon, mostly oceans, and vegetation. According to the IPCC, the total increase in carbon in the atmosphere is only about 4 Gt per year (including anthropogenic emissions). If you do a little math it becomes apparent: if that 9 Gt of emissions caused by humans were not there, then there would likely be no increase in overall concentration. Even though the relative contribution is small, anthropogenic emissions throw the global carbon cycle out of whack.

One good analogy of this process is weight gain. Let's say you average around 2,000 calories of food intake each day, and on average you burn off the same amount each day. If this continues over time, you will not gain weight. But if you add one extra 100 calorie snack each day, it will throw this balance out of whack. Even though you are only increasing your calorie intake by a measly 5%, over time this will cause weight gain. Well, it appears that the earth has put on some serious carbon weight in the past ~200 years, and it is almost entirely due to the extra human emissions!

Fact 3: The Climate Is Warming

Humans have been taking direct temperature measurements since about 1880. There has been an upward trend in global temperature since around 1900, and the increase has become very sharp since about 1980.

Graph of global temperature trends since 1880, it shows a rather steady increase
Figure 3.5: Global average temperature since 1880 (the blue and red lines). Note the sharp increase since around 1980 and the overall upward trend since 1900. The black line indicates carbon dioxide concentration, with the ppm scale on the right.
Credit: NOAA

According to NASA:

"Seventeen of the hottest 18 warmest years in the 136-year record all have occurred since 2001, with the exception of 1998. The year 2016 ranks as the warmest on record."

Based on this evidence (which has been corroborated by other scientific sources) and Figure 3.4 above, it is clear that the global temperature has been increasing since humans have been measuring it on a global scale, and it appears that the warming is accelerating.

One note of caution: The earth operates in cycles of thousands and millions of years, so less than 150 years of warming is not undeniable evidence that the climate will continue to warm. However, the correlation that is observed between increased CO2 levels and temperature, along with what we know about GHGs, is troubling.

Fact 4: If Climate Change Occurs as Many Scientists Believe, the Results Will Almost Certainly Be Catastrophic

There is wide consensus that if the climate continues to change and CO2 levels continue to rise the results will not be good (okay, "not good" is a pretty big understatement). As the Intergovernmental Panel on Climate Change (IPCC) stated in their 2007 report: "Taken as a whole, the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time" (Credit: IPCC, quoted by NASA). This is a stuffy way of saying that "things will probably be really bad and continue to get worse."

The link below outlines some of the possible impacts, some of which have already begun to occur. Note that I am not saying that all of these things will happen, even if climate change continues, but it is meant as a survey of some of the most commonly cited negative impacts of climate change. Also note that some of the likely consequences may be positive in some areas, including extended growing seasons in cool climate zones and some increased growth of plants due to extra carbon being available, but the overall impact will very likely be overwhelmingly negative.

It is also very important to note that the most vulnerable to these impacts will be low-income and otherwise marginalized people all over the world. As the IPCC states in their 2014 assessment:

"(Climate change) risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development" (IPCC, Climate Change 2014 Syntheses Report, p. 13).

Translation: the people with little power and/or resources will be disproportionately affected by climate change, regardless of whether they live in a low- or high-income country. This is thus an important social and environmental justice issue!

Fact 5: There is Broad Scientific Consensus that Humans are Most Likely the Primary Driver of Observed Climate Change

Multiple reports in peer-reviewed journals have found that at least 97% of scientists actively publishing in the climate field agree that the climate change observed in the past century is likely due to human influence, i.e., it is anthropogenic. See these links to some studies. In 2015, 24 of Britain's top "Learned Societies" - groups of scientific experts, basically - wrote a letter urging that we need to establish a "zero-carbon world" early in the second half of the 21st century. In the past 15 years, 18 U.S. scientific associations have confirmed that climate change is likely being caused by humans. Big players in the private sector are concerned as well. For example, CEOs from 43 companies in various sectors (with over $1.2 trillion of revenue in 2014) signed an open letter urging action in April of 2015. Even Exxon Mobil states as their official position on climate change (as of the summer of 2018) that:

"The risk of climate change is clear and the risk warrants action. Increasing carbon emissions in the atmosphere are having a warming effect. There is a broad scientific and policy consensus that action must be taken to further quantify and assess the risks."

Exxon Mobil, the world's largest publicly traded oil and gas company, is not known to be a friend of carbon reduction advocates. In fact, a study published in August of 2017 found that they systematically misled the public for nearly 40 years about the dangers of climate change, even though they acknowledged the risks internally. Yet even they assert that emissions should be reduced.

Putting it All Together

Let's consider these facts together:

  1. We know that the greenhouse effect warms the planet and that carbon dioxide is a greenhouse gas.
  2. We know that humans are emitting greenhouse gases at a rate that is increasing their concentration in the atmosphere.
  3. We know that the global climate is warming.

These three facts alone indicate that there is likely a problem. But, on top of this, you add that:

  • The vast majority of active climate scientists agree that climate change is a problem and that climate change is at least very likely being caused by humans. So, the people that we trust to understand the climate widely agree that it is a problem.
  • Finally, if climate change is happening, then the results will likely be devastating and on a global scale.

Even if we are not certain that humans are impacting the climate (we can never by 100% certain because we only have one planet to run this global "experiment" on), it is probably worth taking the precaution to prevent it if it is true. Yes, it is possible that so many climate experts are wrong - it is a rare occurrence that so many experts are wrong, but there is a possibility, however slim. And yes, we do not know for a fact that humans impact the climate, though basically all signs point to it being the case. And yes, there will be costs associated with making the change to a low-carbon society. But why do people buy life insurance? What about fire insurance? As silly as it sounds, what about buying an extended warranty on a new piece of electronics, or extra insurance for a rental car? The point is that even though the likelihood of using those insurances is minimal - probably less than the likelihood that climate change is caused by humans - people are willing to pay the cost in order to avoid catastrophe. The same could be said of climate change. Taking steps to avoid the worst-case scenario, or perhaps something near the worst-case scenario, is known as the precautionary principle. This may cost money or other resources in the short term, but is seen as worth it because of the situation it may prevent.

One quick addendum to this: If steps are successfully taken to reduce climate emissions to a sustainable level, it is very likely that there will also be cleaner air, less environmental damage, more energy security (not being dependent on another country for energy), and probably more active/healthy citizens. Something to think about.

Further Reading - OPTIONAL

If you are interested in reading more about this topic, here are some suggested readings.

Optional (But Strongly Suggested)

Now that you have completed the content, I suggest going through the Learning Objectives Self-Check list at the top of the page.