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PWS 180: Section 3
How does human activity alter the climate system?
The worksheets, slides, and other materials for this section can be found in this Box folder: PWS180 shared.

Now that you know the primary controls on the Earth’s climate, we now are going to focus on what human activities are affecting the climate system. We will spend the next few weeks exploring how humans have already affected the atmosphere, land, and ocean, as well as what we know about the future trajectory of the Earth system.
  • This week, we are moving beyond how the Earth’s climate has worked before humans came on the scene. Starting a few hundred years, humans started influencing climate on a global scale. We will go over some of those early examples of human-climate interactions and read the most updated version of the extent of our interference today. There are fewer readings than usual, but they are somewhat longer. As always, take your time and ask questions in and out of class:

    1. Reading: Essay by Charles C. Mann on the “State of the Species.” This article takes an unconventional view of our status on planet Earth and the prospects for our future.
    2. Reading: BBC coverage of an important article on how European colonization of the Americas triggered a chain of events that contributed to the Little Ice Age.
    3. Reading: The IPCC Fifth Assessment Report (AR5), Topic 1: Observed Changes and Their Causes. You can download the report here or access the pdf in the shared Box folder. This week, we will read pages 35-54, which includes the Introduction to the topics sections and the first topic.
    4. Reading: Analysis and perspective on the AR5 by the Carbon Brief.

    Here are some additional readings for those who want to dig deeper:

    • The original, 2019 article by Koch and others on the Great Dying and its effects on climate (if you don’t have access, the pdf is in the shared folder).
    • A nice, nontechnical overview by Katherine Hayhoe of what is changing in the Earth’s climate and why a “few degrees” matters.

    Questions to guide (or at least to start) your reading:

    1. In Charles Mann’s article, why does Lynn Margulis say that the fate of every successful species is to wipe itself out?
    2. What do you think changed in humankind that allowed us to expand from our very small initial range ~100,000 years ago to begin filling the world ~50,000 years ago?
    3. Why do some paleontologists and evolutionary biologists think that all humans are so genetically similar?
    4. Biologically, why is there such a drive to consume and reproduce?
    5. Population growth of any species sometimes follows an “S” curve. What causes the two inflection points in that shape (i.e. why does growth accelerate so much and why does it eventually decelerate)?
    6. What is behavioral plasticity, and how does it relate to the future success or collapse of human civilization?
    7. How are population growth and consumption (total and per-capita) linked?
    8. In what ways is the task of constraining or directing human growth “unnatural” or surprising?
    9. How might the decline of slavery, misogyny, violence, and other forms of oppression inform our thinking about change in modern consumption and production patterns?
    10. What caused the “Great Dying” of indigenous people in the Americas during the 16th century?
    11. What did this continental catastrophe trigger in the terrestrial ecosystems and subsequently the atmosphere?
    12. The IPCC report defines risk as a product of hazard, vulnerability, and exposure. What does this mean?
    13. T/F High risk occurs when you have high probability outcomes with severe consequences.
    14. How does the IPCC assign different levels of certainty (likelihood) to the research it synthesizes?
    15. How much has global temperature changed since 1850?
    16. How much has minimum Artic Sea Ice changed since 1900?
    17. T/F Sea level has not yet changed since 1900, but if warming continues, it could rise substantially
    18. How much of the extra heat caused by anthropogenic climate change is in the atmosphere versus the ocean?
    19. What are the four most important anthropogenic greenhouse gases?
    20. How much is a gigaton of carbon? How does it relate to a gigaton of CO2?
    21. Globally, what economic sectors produce the most greenhouse gas?
    22. How can greenhouse gases account for more than the warming we have observed?
    23. T/F Climate change is primarily of concern because it could push certain vulnerable species over the edge.
    24. What is the difference between mitigation and adaptation regarding climate change?
    25. What is the cryosphere and why is it important to current human society?
  • This week, we are focusing on how human activity is reshaping the atmosphere and the climate system. What activities are causing the changes, how do we know it’s humans, and which humans are contributing the most?

    1. Listening (1 hour 26 minutes): Kate Marvel interview on the Ezra Klein show on climate models, uncertainty, and how to understand climate change. This interview is pretty wide ranging, and Dr. Marvel  goes into projections of future climate and potential individual and political responses to those changes. However, I think that Dr. Marvel does a marvelous job at making technical climate simulations understandable, and I think this interview provides an interesting starting point for the rest of the semester.
    2. Reading: The Wikipedia article on Global Warming Potentials. In typical Wikipedia style, this article efficiently presents the main concepts surrounding how we compare different greenhouse gases. This is a complex subject, but really important moving forward.
    3. Watching (5 minutes): The Denial 101 episode on Consensus of Evidence. This episode succinctly summarizes some of the ways we know that greenhouse gas increases and consequent warming are due to humans.
    4. Watching (9 minutes): Katherine Hayhoe on Fossil fuels and renewable energy. This episode explains how important fossil fuels have been in the past, and why it is so important that we transition to better sources of energy for the future.
    5. Reading: The World Resources Institute’s greenhouse gas emissions by countries and sectors. This WRI report provides detailed information about the sources of greenhouse gases. You could spend hours with their interactive figures and learn a lot. For the purposes of this week, focus on what economic sectors and what countries are producing the most greenhouse gases.
    6. Reading: The US Environmental Protection Agency’s webpage on sources of greenhouse gas emissions in the U.S. The EPA’s webpage is a clear and direct dashboard for emissions in the US. Feel free to click on the different tabs to get more detail about each sector.
    7. Reading: The Global Carbon Budget summary highlights. We will be reading full articles by the Global Carbon Project soon, but this week we are focusing on the summary updates for 2019. The article is very short but stuffed full of important information about the state of the carbon cycle.

    Additional readings:

    Questions to guide (or at least initiate) your reading and thinking:

    1. What is a climate model?
    2. What is climate sensitivity?
    3. How do we know that the increase in greenhouse gases and consequent warming are due to humans?
    4. What are CO2 equivalents and why do we use such convoluted units to understand greenhouse gas emissions?
    5. What is “global warming potential,” and why is it so different depending the gas and the timescale chosen?
    6. What was the total amount of greenhouse gases produced by humankind in 2019?
    7. At a global scale, what sectors of the economy are contributing the most to climate change?
    8. Are the same emissions patterns true within the U.S.?
    9. T/F Fossil fuels have always been a negative factor in human development.
    10. What percentage of cumulative greenhouse gas emissions have been produced by the U.S.?
    11. What percentage of current greenhouse gas emissions are produced by the U.S.?
  • This week, we are reading about changes through time in human emissions. How have we tried to reduce greenhouse gas emissions and how effective has it been? There are fewer readings than usual, but two of them are peer-reviewed articles. Make sure to give yourself enough time to process them and take careful notes.

    1. Reading: Wikipedia article on the Paris Agreement
    2. Reading: Peters et al. 2019. This article from the journal Nature Climate Change reports the detailed results of the Global Carbon Project’s 2019 report. Pay attention to how different sectors of fossil fuel are changing and in what regions the changes are happening. (PDF in the shared folder, if you don’t have access)
    3. Reading: Jackson et al. 2019. This article from the journal Environmental Research Letters compares greenhouse gas emissions with commitments from the Paris Agreement. Pay special attention to the global and regional trends over the past 20 years in greenhouse gas emissions.
    4. Watching: Global Weirding video on background on fluorinated gases, ozone, and climate change by Katherine Hayhoe. This video links a major environmental success (combatting the ozone hole) with current efforts to reduce greenhouse gas emissions.

    Additional readings:


    1. What are the global trends in greenhouse gas emissions over the past 50 years?
    2. What factors are preventing global greenhouse gas emissions from falling enough to meet the Paris Agreement?
    3. What countries are the biggest contributors of greenhouse gases?
    4. What are the trends of greenhouse gas emission for those countries?
    5. How much of an effect do you think the U.S. retraction from the Paris Agreement had on national and global climate response?
    6. How are the ozone hole and climate change connected?
    7. What is an example of solving a global environmental problem, or are we doomed to fail?
    8. T/F Fossil fuels have always been a net negative factor in human civilization.
    9. What are some proposed mechanisms for meeting the Paris Agreement?
    10. What is your sense for what the scientific authors we read this week believe about the prospect of limiting climate change to 2C or 1.5C (i.e. are they optimistic or pessimistic)?