Instructors:

Peter Huybers and Eli Tziperman

TF:

Aleyda Trevino

Time:

Wednesday, 3-5:45pm.

Location:

Museum of Comparative Zoology, 4th floor, 440 (Harvard University Center for the Environment)

Bibliography:

Papers are posted on the course web page and linked from this document.

Announcements:

Last updated November 28, 2021. Feel free to write, call or visit us with any questions.

Want to be an informed climate skeptic? Come learn from other people’s mistakes…This reading course seeks to provide an overview of the science of global change thorugh a survey of current scientific debates. Topics are specifically chosen for their relevance, interest, and open-ended nature. No correct answer is likely to emerge, but we hope that you will become scientifically better informed regarding relevant climate topics. An initial list of topics are provided below, but this can be revised according to current events and student interests.

Prerequisites: This broad survey course is designed to be accessible to upper level undergraduate students who have a scientific background. APM21A and APM21B, or equivalents, or permission of instructor, are required.

Presentation: Each group of 2-3 students will be responsible for preparing and making both a preview presentation and a full presentation regarding a few of the subjects. The preview presentation is ~5 slides, 10 minute long, and is given the week before the subject is discussed in class. The purpose of this brief presentation is to motivate the subject, explain its importance, and especially help the other students understand the reading material by providing them some guidance and explanation about the paper(s) and the relevant background. The full presentation is ~30 slides long and is to be used during the discussion. Please provide some background for the other students and then get to the actual scientific topics within ~5 slides. The purpose of this presentation is to guide and excite discussion, rather than to lecture. Not actually covering all 30 slides during class time would be just fine. Presentations are to based upon the assigned reading and augmented with additional material. See course requirements and guidelines here, writing and presentation guidelines here, example slide here and an example presentation here.

Position paper If not part of the group making a full presentation in a given week, students are asked to bring a one-page position statement (12pt single space) to class based upon the assigned reading where the first part outlines the overall issue and the second provides an initial judgement on the topic.

Grading: Based on presentations (30%), discussion and participation (30%), and position papers (40%). If you must miss class, which obviously makes participation impossible, please obtain our permission ahead of time.

(All reading material is hosted here)

See links for all topics on following pages.

1. Jan 30, First meeting: we start by watching the “skeptics”: the movie “An Inconsistent Truth”, or “The great swindle of global warming;” please prepare by perusing “the climate of man” in the Intro and background folder, or watch Steve Goreham.
2. Feb 6: Arctic sea ice melting
3. Feb 13: Hurricanes
4. Feb 20: Ocean heat uptake is increasing
5. Feb 27: Sea level rise acceleration during 20th century
6. March 6: Sahel droughts
7. March 13: Western U.S. forest fires
   

   March 20: spring break.
   

8. March 27: Cosmic-rays
9. April 3: Antarctic ice sheet instability
10. April 10: Ocean acidification/ coral bleaching
11. April 17: Social Upheaval
12. April 24: Geoengineering
13. May 1: Last class

1. Radiative Balance What is Earth’s net radiative forcing? Read Trenberth and Fasullo (2012), who can’t find the extra heat accumulating from Earth’ radiative imbalance, and then Loeb et al. (2012) who argue that the heat budget balances to within uncertainty. readings.
2. Cosmic Rays: Is global warming due to a change in cosmic rays? First, note the striking(…?) Similarity between the globally averaged temperature and the curve showing cosmic rays arriving to the Earth, 1-global-temperature-vs-cosmic-rays.pdf, although note that this looks much less convincing with updated data shown there. A non-technical summary of the issue from a few years ago is given in 2-RealClimate-cosmic-rays-still-not-convincing.pdf. The two readings this time are somewhat technical, you only need to read the highlighted parts: First, 3-Dunne-etal-2016.pdf discusses a very thorough experimental and modeling study of the effects of cosmic rays on clouds and conclude that the effect is negligible. However, 4-Svensmark-etal-2017.pdf discuss a theory and an experiment which they believe show an important effect of cosmic rays on climate. readings.
3. CO₂ saturation: Isn’t the atmosphere saturated with respect to longwave trapping by CO₂ anyway? If so, additional CO₂ cannot absorb more heat and wont enhance the greenhouse effect, so nothing to worry about? This issue started with the debate between Arrhenius (calculated the expected warming due to CO₂ doubling) and Angstrom Jr (measured the radiative effect of additional CO₂ and concluded that it’s negligible). Read the two RealClimate blog entries. readings.
4. The infrared (LW) ”iris effect”: will cloud feedbacks prevent global warming? Background: The iris effect is a proposed cloud feedback that may reduce global warming. Does it work? (1) Read the short wikipedia entry; [optional, see Lindzen et al BAMS paper under the more/ directory]. (2) Lindzen and Choi (2009) try to make the case for an Iris based on present-day observations. (3-4) Trenberth et al (2010 paper and a brief RealClimate summary by the same authors) criticize them. And finally (5) Lindzen and Choi try again, addressing the criticisms they received, claiming their results are still robust. readings.
5. Why is the stratosphere cooling? readings.
6. Climate sensitivity: How sensitive is temperature to radiative forcing? Wikipedia gives an overview of what is meant by the term “climate sensitivity”. Note the distinction between transient climate sensitivity and equilibrium climate sensitivity. Then read the 1979 National Academies report on climate sensitivity whose estimate has generally stuck (Charney et al., 1979), and then contrast this with one recent estimate that is lower (Aldrin et al. 2013). readings.

   Atmosphere

7. Heat waves: Are they due to global warming, or just a statistical fluke? Start with the NYTimes article on the Russian heat wave. Then Read Dole et al (2011) suggesting that this has nothing to do with global warming. Then, from Otto et al (2012) who try to provide a more refined view, read the introduction and conclusions and the discussion around Figure 4. [Optional: the rest of Otto et al, and Rahmstorf and Coumou (2011) in the more folder, claiming that this heat wave would have been very unlikely without global warming]. readings.
8. Extreme precipitation and floods: will intense rain events become even more intense, leading to more floods? The physics behind this projection seems robust (at least outside the tropics), but have we seen this increase in flooding already? Can recent dramatic floods be attributed to this anthropogenic effect? readings.
9. Mid tropospheric warming: Is the upper troposphere warming more than the surface? Why is this expected in principle? Is the model prediction for such warming (especially in the tropics, 200–300mb) exaggerated relative to radiosonde satellite observations? Read first Douglas et al (2008) making the case that models are badly biased. Then the RealClimate entry explaining that this debate is not new and that the model-radiosonde discrepancy has already been resolved. Finally, read Santer et al (2008) trying to make the case that models are now consistent with observations (look carefully at their figure 6, are you convinced that the models are absolutely great?) readings.
10. Jet stream waviness and cold winters: could global warming and the loss of summer sea ice lead to cold winters in North America via induced strong waviness of the atmospheric jet stream? read the perspective piece by Wallace et al. (2014) and make a note of the arguments that they raise against the notion of Arctic sea ice influencing mid-latitude weather. Then read Francis and Vavrus (2012) and the counter-argument by Barnes (2013). Finally, read thedot.earth entry, which includes some back and forth between the various authors. Optional: folder with articles from the popular press. readings.
11. Sahel Droughts: will the Sahel become drier or wetter? First, read Thomas and Nigam (2018) who discuss drying and expansion of the Sahara and discrepancies between their observational estimate and climate model simulations. This is a long paper, and you need only read the parts that are highlighted. Second, read Schewe and Levermann (2017) for a discussion of how climate model simulations indicate a wetter Sahara in the future. readings.

    Oceans

12. Ocean heat uptake is increasing? Models suggest that ocean heat uptake should be accelerating — do the data show that it is? Is the ocean absorbing heat faster than previously estimated? Does it save us from extreme warming? readings.
13. did sea level rise start accelerating? in recent decades due to anthropogenic global warming, or did it start accelerating 200 years ago due to natural reasons? readings.
14. (older debate) Sea level rise after last glaciation: From where did rapid rise in sea level during the last deglaciation originate? Read a very short introduction on uncertainty in future sea level and an event known as Meltwater Pulse 1a. Then read Clark et al. (2002) on “fingerprinting” the source of Meltwater Pulse 1a to Antarctica. If interested, skim the recent New Yorker piece on how sea level rise is affecting Southern Florida. Recent references that build on Clark et al. (2002) are in the More directory, along with the full IPCC chapter on sea level. readings.
15. (older debate) will sea level rise exponentially? read the executive summary and section 13.8 from the IPCC report. Then the highlighted parts of the controversial Hansen et al (2015) paper claiming that the sea level will rise much more than predicted by the IPCC. Finally, read [3,4] for some of the reactions to this paper. readings.
16. Ocean acidification: It’s an undisputed consequence of rising CO₂, but the exact effects on calcifying species and the carbon cycle is still in question, and we’ll take a closer look with the following articles, posted on the website: (1) Read the RealClimate entry which sums up the chemistry nicely. (2) Lohbeck et al (2012) which suggests that organisms can evolve to adjust. readings.
17. Ocean circulation failure: Could ocean circulation change rapidly? Readings: (1.) [about 3 pages] [2.5 pages] Bryden et al., 2005 ”Slowing of the Atlantic meridional overturning circulation at 25N”: the actual scientific paper suggesting that the THC has already collapsed. (2.) A more recent paper showing how variable the ocean overturning circulation is. (3.) [half a page] An (unpublished) explanation of the ocean circulation ”collapse” in terms of the overturning circulation seasonal cycle: readings.
18. More or stronger hurricanes due to global warming: Background: 2005 was a destructive hurricane year, global warming was blamed. Some of the following seasons were not as dramatic. What’s going on? Which ocean temperature affects hurricane intensity? Emanuel (2005) found a correlation with Atlantic SST which predicts stronger future hurricanes, other studies find correlation with remote SST which leads to opposite future projections. readings.
19. (older debate) More or stronger hurricanes due to global warming: Can we accurately reproduce past Hurricane activity? Read at the following order: (1) Emanuel (2005) ’Increasing destructiveness of tropical cyclones over the past 30 years’; (2) Landsea et al (2006) ’Can We Detect Trends in Extreme Tropical Cyclones?’; [Optional: in the more/ directory, including the interesting resignation letter (Landsea-letter-resigning-from-IPCC.pdf).] readings.
20. Hiatus: Has global warming stopped since 2000? Please read the blog entry by Judith Curry explaining the IPCC position and arguing it’s confused at best. Continue with the one page Held (2013) which summarizes the next paper, and then read Kosaka and Xie (2013) which suggest an explanation for the Hiatus (tropical Pacific). readings.
21. Methane clathrates: Could significant amounts of Methane clathrates/ hydrates on the ocean floor be destabilized and released to the atmosphere due to global warming, causing a catastrophic positive feedback? See wikipedia and then the two sides of the debate. readings.
22. Permafrost thawing and emissions: another positive feedback? readings.

    Cryosphere

23. Antarctic ice sheet instability: How fast could West Antarctica melt? First watch what glacier calving looks like here. Then read Pollard et al. (2015) readings. If you want more background, look at the review article by Alley et al. in the More folder, or you can watch Alley lecture on this topic here.
24. Mountain Glaciers: Are mountain glaciers melting? Due to global warming? First, see some beautiful pictures of glaciers ”before and after” here; then note that the IPCC 4th Assessment Report stated, “Glaciers in the Himalaya are receding faster than in any other part of the world (see Table 10.9) and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high if the Earth keeps warming at the current rate. Its total area will likely shrink from the present 500,000 to 100,000 km2 by the year 2035 (WWF, 2005).” (IPPC 2007, Working Group II: Impacts, Adaptation and Vulnerability, Chapter 10.6.2); read Bloch et al. (2012) about the Karakoram and Himalayan glaciers and the one-age comment by Cogley (2010) on the source of misinformation in the IPCC. Optional: see Kapnick (2014) for more on the Karakoram glaciers and here for more on the IPCC process and how it failed in this particular case. readings.
25. Changes in sea ice: Does Arctic sea ice melting have anything to do with global warming, and why is Antarctic sea ice increasing? First read the short EOS overview by Overland et al (2008) and then the more detailed piece by Overland and Wang (2010). For a different view of Arctic ice loss as a positive feedback, see Screen and Simmonds (2010). Finally, Maksym et al. (2012) round out the discussion regarding Antarctic sea ice, contrasting it against its polar opposite. Also, see two nice NASA animations, and the readings.
26. How quickly will Greenland melt? and could it contribute to significant sea level rise in the next century? Are ice streams there already accelerating? We will focus on the significant changes that have been observed in Greenland in the last ten years. The three readings (Hansen 2007; Nick 2009; Pfeffer 2008) take different positions on the question of future sea level rise primarily based on the potential for ice stream changes due to ocean and atmospheric forcing. [Optional: material on ice streams (helps to understand the Nick et al. paper) readings is given in the Joughin & Alley paper on ice streams, section on internal instabilities. For more on ice streams, the Bennett article.] readings.
27. Can the west Antarctica ice sheet collapse? readings.

    Paleoclimate

28. Is the 20th century warming unusual? The “hockey stick” controversy. The IPCC report in 2001 prominently figures a reconstruction of past temperatures from Mann et al. which is often referred to as the hockey stick because it features a slow and straight decline in temperature followed by a sharp uptick in the last century. This reconstruction came under criticism for the statistical techniques which were employed. Please read: (1) RealClimate summary of the hockey stick controversy. (2) [5.5 pages] Mann et al. ”Global-scale temperature patterns and climate forcing over the past six centuries”. Read up to page 784, not including the section ”Attribution of climate forcings”. (3) McIntyre and McKitrick, ”Hockey sticks, principal components, and spurious significance”. readings.

    One remarkable part of this specific debate is the involvement of the US congress. Please read under the directory Mann_vs_US_congress/: (4) Congressman Barton’s letter to Mann and Mann’s response. [Optional: if you’d like to learn more about the popular press response to this debate, look under popular-press/, especially at the Guardian article.] readings.

29. Do temperature variations lead CO₂ changes during ice ages? (i) Using your own web search results, start by describing the snow accumulation process during which gas bubbles are trapped in ice cores, what is the time scale of bubble trapping in Antarctica? In Greenland? Why is there a difference? (ii) Using the above, explain what are gas ages and ice ages and what sets the difference between them. (iii) Proceed to read the assigned papers and discussing them in your report following the course guidelines: (1) RealClimate entry posted on the course web page. (2) Caillon et al. (2003). (3) The short perspective piece by Brook (2013). (4) Parrenin et al. (2013). Caillon (2013) argues that temperature leads CO₂ during glacial terminations (e.g., during the exit from the last glacial maximum some 20,000 years ago) and Parrenin et al. (2013) argues the opposite. Do we really know which leads and which lags? According to climate skeptics, a lead of CO₂ relative to temperature means that it is not necessarily important in this warming process. Do you agree? readings.
30. Anthropocene: did early humans started altering climate through modifying atmospheric composition thousands of years ago? Did they stop an ice age from occurring? Bill Ruddiman has proposed that the human influence on climate started more than 5000 years ago, but others see climate variability prior to a couple of centuries ago as arising essentially only from natural processes. How far back does our influence reach? Readings: 1. Scientific American article by Ruddiman (2005): ”How did humans first alter global climate?”; 2. Criticism: ”The Holocene CO₂ Rise: Anthropogenic or Natural?”, by Broecker and Stocker, 2006; 3. The reply: ”On ”The Holocene CO₂ Rise: Anthropogenic or Natural?”, by Ruddiman 2006. [Optional: 4. Original laying out of the idea: ”The anthropogenic greenhouse era began thousands of years ago”, by Ruddiman 2003; 5. A third opinion, ”How Long Will Our Interglacial Be?”, by Crucifix and Berger, 2006; 6. A recent 2013 update by Mitchel et al, for the past ~3000 years only, though.] readings.

    Biosphere

31. Amazon forest die-back: A potential carbon feedback that has been heavily debated in the literature. Cox et al. is an analysis of results from a comprehensive global circulation model (GCM) which includes dynamic vegetation effects, in an effort to simulate the response of the biosphere to climate change. Malhi et al. takes a different approach by focusing on the hydrological characteristics that contribute to the existing biome distribution. We will be engaging with two questions: 1) What is the expected response of the Amazon to climate change? 2) What will be the feedback (if any) of changes in terrestrial vegetation on the global carbon cycle (and hence, the climate)? readings.
32. CO₂ fertilization: plants grow better under higher CO₂? So what’s the problem? readings.
33. Methane emission from plants: Living terrestrial vegetation emits large amounts of methane into the atmosphere. This surprising recent finding may have an impact on accounting of greenhouse-gases and of sources of methane: readings.

    Broader implications

34. Social Upheaval: is it precipitated by climate variations? More wars in warmer climate? Our two readings this week examine the link between ENSO and civil conflicts, while examining the extent to which warm temperatures are associated with elevated levels of armed conflict in Africa. readings.
35. Food shortage? Is agricultural food production going to decrease dramatically due to global warming? Read Schlenker et al 2009 suggesting that high temperatures will decrease crop yield. Then Butler paper explaining that adaptation can make all the difference, then the comment/ reply. readings.
36. Forest fires? Is global warming causing more severe forest fires? Or is it forest management? First read the New York Times piece that broaches the climate change versus management question, then the paper by Abatzogloua and Williams (2016) that makes the case for a major contribution by climate change, and finally the blog post by Morris (2015) arguing that management decisions are primarily to blame for increasing forest fire activity. readings.
37. Mental Health. Does global warming already lead to an increase in mental health issues? readings.

    But what to do?

38. How best to control emissions: Read the Rolling Stone article by Bill McKibben (2013) and Hansen et al. (2013) for arguments that net fossil fuel extraction must be limited, and Schrag (2012) that our focus should be on spawning the innovation needed to transition away from carbon-emissions-based energy production. readings.
39. Should geo-engineering be studied and employed? Discuss the concept of geo-engineering. What strategies have been proposed? How does it work? Is it feasible? Is it ethical? Discuss the pros and cons of mitigation and geo-engineering. Under which conditions would its utilization be appropriate? How would you propose to manage our risk exposure to future climate change? readings.

    More

40. Prediction and projection: Are General Circulation Models rigged? (Knutti 2007, Charney Report)
41. “An inconvenient truth” Al Gore’s global warming movie.
42. Last class: Congratulations, we’ve reached the end. Please submit a one half summary of the readings for this week. In addition, please respond to our survey email, and summarize your overall lessons from the course in another half a page text. Incorporate material from the debates we covered and conclude with your own assessment of the scientific basis for present and future global warming.