Fall 2019   


Global warming debates - a guided reading course


Instructor: Eli Galanti 


Monday, 9:15-11:00 - Magaritz seminar room, Sussman building                      TA: Ilai Guendelman



NEW! Four classes will be devoted to HANDS-ON-learning a mechanism controlling a global warming phenomenon. We will use Python for calculations; hence each student is required to install the latest Anaconda application on his/her computer. Please bring your laptops to class.





Week 01

(Nov 04)

Eli & Eli


Introduction (Hands-on learning)


Week 02

(Nov 11)

Dana & Tom


Sea level rise acceleration


Week 03

(Nov 18)

Eli & Eli


Hurricanes (Hands-on learning)


Week 04

(Nov 25)

Ichiko, Lior & Stav


Amazon forests dieback


Week 05

(Dec 02)

Ran, Ambikesh & Carmen


CO2 saturation


Week 06

(Dec 09)

Eli & Eli


Temperature (Hands-on learning)


Week 07

(Dec 16)

Emmanouil & Iris


Antarctic ice sheet instability


Week 08

(Dec 23)

Eli & Eli


Droughts (Hands-on learning)


Week 09

(Dec 30)

Rita & Yehonatan


Heat waves


Week 10

(Jan 06)

Eli & Eli


Ocean acidification (Hands-on learning)


Week 11

(Jan 13)

Yael, Hagar & Lital


Mountain glaciers


Week 12

(Jan 20)

Eli.W & Yuval


Jet waviness


Week 13

(Jan 27)

Ron, Yinon & Nitai


Ocean circulation failure


Week 14

(Feb 03)

Or & Jonathan





Overview & goals


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 thorough a survey of current scientific debates. Topics (see below) 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 is provided below, but this can be revised according to current events and student interests.




Prerequisites: This is a basic introductory breadth course and should be accessible to all Weizmann graduate students.


Requirements: Apart from reading all assigned papers, students will be asked to prepare presentations on one or two of the topics to be covered during the course and based on the appropriate papers posted on the course web page, and lead a discussion during class. In addition, each student not part of the presenting group should turns in a half page position paper on each week subject. Finally, class attendance is mandatory.


NEW! About four classes will be devoted to HANDS-ON-learning a mechanism controlling a global warming phenomenon. We will use Python for calculations; hence each student is required to install the latest Anaconda application on his/her computer.


Position papers: 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 judgment on the topic.


Presentations: Please organize in groups of 2-3 for this purpose and choose subjects from the topics (see below) you would like to work on (keep in mind, it’s a first come first served base). Depends on the number of students, each group will work on one or two topics.

Each topic will require two presentations by the students leading the corresponding discussion. The first presentation is ~5 slides, 10 minutes long, and is given the week before the subject is discussed in class. The purpose of this brief presentation is to motivate the subject, and especially help the other students understand the more difficult aspects of the reading material. The second presentation is ~30 slides and is to be used during the discussion. Please provide some background for the other students, but then get to the actual paper within 5 to 6 slides. Please show the figures and equations from the paper, explain them, and provide guiding questions. In particular, make an effort to excite a discussion about the reading material. That is, the purpose of this presentation is to guide discussion, as opposed to supporting a lecture. Note that we may not cover all 30 slides if the discussion uses all the class time, and that this would be a good indication of a successful presentation. Make sure to switch presenting between group members every slide, rather than dividing the presentation into larger blocks.


Grading: Based on presentations (40%), position papers (40%), and participation (20%).



A list of topics



  1. Introduction: The movie  The great swindle of global warming”.

ü  Read [1] the article "Don't believe the hype". Skim through [2] the "IPCC summary for policy makers" and consider watching the series of short YouTube movies. In class we will also discuss the course requirements and give guidelines for each of the assignments.

ü  Important! please install Anaconda on your laptop and bring it to class. We will show an example of a Python script and ask all the students to work with it during class.

ü  Readings.


Radiative forcing

  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 raysIs global warming due to a change in cosmic rays?

ü  This time we will be reading a few small bits from several papers and blogs, please follow instructions 1-5 carefully: [1] Start by looking at the global-average temperature record and [2] the flux of cosmic ray (page 8, Fig. 6) and note the remarkable similarity of the global temperature record and this cosmic ray record. Both reach a max around 1950, a minimum in the 1970s, and then increase. A strong case that solar activity is the source of global warming?  Then read [3] the Svensmark paper that proposes a physical mechanism that links the solar activity and the global temperature. Continue by reading [4] for a discussion of systematic errors in solar activity data, and finally see [5] a critical discussion of the physical mechanism linking cosmic rays and cloud condensation nuclei. Readings.

  1. 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).

ü  Read [1,2] the two RealClimate blog entries. Also consider reading [3] the chapter on greenhouse gasses. Your summary should be on [1] and [2]. Readings.

  1. 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.
  2. Why is the stratosphere cooling? Readings.
  3. 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.



  1. Heat wavesAre they due to global warming, or just a statistical fluke?

ü  Start with [1] the NYTimes article on the Russian heat wave. Then read [2] Dole et al (2011) suggesting that this has nothing to do with global warming. Then [3] Rahmstorf and Coumou (2011) claiming that this heat wave would have been very unlikely without global warming. Finally, read [4] Otto et al (2012) which try to reconcile the two views. Readings.

  1. 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.

9.     More or stronger hurricanes due to global warming: 2005 was a destructive hurricane year and global warming was blamed. The following seasons were not as dramatic, but then 2017 broke all records. What’s going on?

ü  Read [1] Emanuel (2005) who came with a simple but brilliant measure for the hurricane destructiveness potential, showing that it has increased dramatically during the past few decades with a strong correlation with the local SST. Then read [2] Swanson (2008), sections 1-2, who shows that hurricanes can also be correlated with non-local SST. Finally, read [3] Vecchi et al. (2008) who demonstrate how the assumptions made by [1] and [2] have fundamental implications for the expected response of hurricanes to global warming. To get an up to date notion on what is expected to happen read [4] box 1 in Knutson (2010).  Readings.

  1. Jet stream waviness and cold winters: Could global warming and the loss of summer sea ice lead to colder winters in North America via induced strong waviness of the atmospheric jet stream?

ü  Read [1] 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 [2] Francis and Vavrus (2012) and [3] the counter-argument by Barnes (2013). Finally, read [4] the NYT article which includes some back and forth between the various authors. Optional: folder with articles from the popular press. Readings.



  1. When 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.

12.  Sea level rise: How fast would the see level rise under global warming?

ü  Read [1] the IPCC prediction of up to 1m sea level rise till the end of the century (Executive summary and section 13.8). Then [2] 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] some of the reaction to this paper. Readings.

13.  Sea level of the past: From where did rapid rise in sea level during the last de-glaciation originate?

ü  Read [1] a very short introduction on uncertainty in future sea level and an event known as Meltwater Pulse 1A. Then read [2] Clark et al. (2002) on “fingerprinting” the source of Meltwater Pulse 1A to Antarctica, and then [3] Liu et al. (2015) who claim such a conclusion cannot be made. If interested, skim the 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.

14.  Ocean acidification: It’s an undisputed consequence of rising CO2, but how would the calcifying marine species respond to the more acid water is not clear.

ü  Read [1] the RealClimate entry which sums up the chemistry nicely*. Then [2] Lohbeck et al (2012) which suggests that organisms can evolve to adjust. Readings.

*For a more detailed review consider reading Doney et al. (2009).

15.  Ocean circulation failureCould ocean circulation change rapidly due to global warming?

ü  Read [1] Bryden et al. (2005) that suggested that the THC has already collapsed. Continue with [2] a more recent paper showing how variable the ocean overturning circulation is. Then read [3] an (unpublished) explanation of the ocean circulation ”collapse” in terms of the overturning circulation seasonal cycle. Readings.

16.  The HiatusHas global warming stopped during 2000-2013?

ü  Read [1] the blog entry by Judith Curry explaining the IPCC position and arguing it’s confused at best. Continue with [2] the one page Held (2013) that summarizes the next paper, and then read [3] Kosaka and Xie (2013) that suggest an explanation for the Hiatus. Readings.

17.  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.

18.  Permafrost thawing and emissions: another positive feedback? Readings.



  1. Antarctic ice sheet instabilityHow fast could West Antarctica melt?

ü  First watch what glacier calving looks like here. Then read [1] Pollard et al. (2015) that make the case for fast collapse, and [2] Bell et al. (2017) that claim the opposite. 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.  Readings.

  1. Mountain glaciersAre mountain glaciers melting? Is it 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).

ü  Read [1] Bloch et al. (2012) about the Karakoram and Himalayan glaciers and [2] the one-page comment by Cogley (2010) on the source of misinformation in the IPCC. Optional: see here for more on the IPCC process and how it failed in this particular case. Readings.

  1. Changes in sea iceDoes 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.
  2. 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.



  1. Is the 20th century warming unusualThe “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 that were employed.

ü  Read: [1] RealClimate summary of the hockey stick controversy, then [2] 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”. Finally, read [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.

  1. 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.
  2. Anthropocenedid early humans start 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?

ü  Read [1] the Scientific American article by Ruddiman (2005.). Then [2] the criticism by Broecker and Stocker (2006), and [3] the reply by Ruddiman 2006. Readings.



  1. Amazon die-back: Will the Amazon forest die because of global warming?

ü  Read [1] (sections 1,4, 7,9) and Cox et al. who analyze of results from a comprehensive global circulation model (GCM) that includes dynamic vegetation effects, in an effort to simulate the response of the biosphere to climate change. Then [2] (marked sections) Malhi et al. who takes a different approach by focusing on the hydrological characteristics that contributes to the existing biome distribution. Finally, read [3] Levine et al. (2016) who used a more comprehensive approach. 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.

  1. CO2 fertilization: plants grow better under higher CO2? So what’s the problem? Readings.
  2. 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

  1. 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.
  2. 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.


But what to do?

  1. 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.
  2. Geo-engineering: Should geo-engineering be studied and employed to mitigate global warming? 

ü  Read [0] the Wikipedia page on Solar radiation management, then [1] Keith (2018) who is supporting the idea, and [3] Pierrehumbert (2017) who warns against humankind ‘hacking the planet’. Readings.