Uncertain 2 Degrees

1. Uncertain 2 Degrees J. Baehr, I. Hense, L. Kutzbach, S. Rödder, M. Scheffold, J. Scheffran Session 2, 10.04.2019 Uncertainties relevant for the discussion of the 2-degree target Lecturer: Lars Kutzbach Course coordination: Lars Kutzbach, Simone Rödder, MaikeScheffold Contact for all inquiries: Maike Scheffold (maike.scheffold@uni-hamburg.de)

2. Today’sSchedule • What is the 2-degree target? • Plenary discussion • Input from Kutzbach • Sources of uncertainty relevant for the discussion of the 2-degree target • Student groupdiscussion • Plenarydiscussion • Inputs from Kutzbach • Is doubt a bad thing? Some thoughts on science ethics • Homework assignment no. 2 (due 13th April)

3. Whatisthe 2-degree target? PlenaryDiscussion

4. Whatisthe 2-degree target? The Paris agreement 2015: Paris Agreement under the United Nations Framework Convention on Climate Change (UNFCCC): “… Article 2 This Agreement, in enhancing the implementation of the Convention, including its objective, aims to strengthen the global response to the threat of climate change, in the context of sustainable development and efforts to eradicate poverty, including by: Holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change; …” United Nations (2015). https://unfccc.int/sites/default/files/english_paris_agreement.pdf

5. Whatisthe 2-degree target? Somehistory • Already in the 1960s and 1970s, • scientificdiscussions (e.g., Ward and Dubos, 1972) on: • Whataretheeffectsofanthropogenic GHG emissions on theclimate? • What is the level of acceptable climate change? • What exactly should be stabilized? Emissions, concentrations, or temperature? Equilibrium change or rate of change? • Early landmark paper by Manabeand Wetherald (1967): • According to a heat balance model, temperature response to doubling CO2concentrations approximately 2 °C.

6. Whatisthe 2-degree target? Somehistory William Nordhaus (Nobel laureate 2018) in 1977: “As a first approximation, it seems reasonable to argue that the climatic effects of carbon dioxide should be kept within the normal range of long-term climatic variation. According to most sources the range of variation between distinct climatic regimes is in the order of ±5°C, and at the present time the global climate is at the high end of this range. If there were global temperatures more than 2 or 3°C above the current average temperature, this would take the climate outside of the range of observations which have been made over the last several hundred thousand years.” • Economiccost-benefitanalysisof various policies to mitigate climatic responses • ThresholdfortemperatureequilibriumchangederivedfromcomparisonwithtemperaturesoverthelateQuaternary (severalglacialcycles) Nordhaus (1975, 1977a, b)

7. Whatisthe 2-degree target? Somehistory 1992: United Nations Framework Convention on Climate Change (UNFCCC), opened for signature at the Earth Summit in Rio de Janeiro: “… Article 2 Objective The ultimate objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. …” United Nations (1992). https://unfccc.int/resource/docs/convkp/conveng.pdf

8. Whatisthe 2-degree target? Somehistory 1996: The European Council of Environment Ministers declared: “… global average temperatures should not exceed 2 degrees above pre-industrial level and that therefore concentration levels lower than 550 ppm CO2 should guide global limitation and reduction efforts.” European Council (1996). http://europa.eu/rapid/press-release_PRES-96-188_en.htm?locale=en

9. Whatisthe 2-degree target? Somehistory 2009: Copenhagen Accord: “… 1. … To achieve the ultimate objective of the Convention to stabilize greenhouse gas concentration in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system, we shall, recognizing the scientific view that the increase in global temperature should be below 2 degrees Celsius, on the basis of equity and in the context of sustainable development, enhance our long-term cooperative action to combat climate change. …” United Nations (2009). https://unfccc.int/resource/docs/2009/cop15/eng/l07.pdf

10. Whatisthe 2-degree target? The Paris agreement 2015: Paris Agreement under the UNFCCC: “… Article 2 This Agreement, in enhancing the implementation of the Convention, including its objective, aims to strengthen the global response to the threat of climate change, in the context of sustainable development and efforts to eradicate poverty, including by: Holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change; …” United Nations (2015). https://unfccc.int/sites/default/files/english_paris_agreement.pdf

11. What is the 2-degree target? CO2 effects on temperature Almost linear relationship between cumulative CO2 emissions and projected global temperature change to the year 2100 TCRE: transientclimateresponse to cumulative carbonemissions IPCC (2014)

12. What is the 2-degree target? Risks of higher temperature Risks from climate change depend on cumulative CO2 emissions IPCC (2014)

13. What is the 2-degree target? Carbon budgets AR5 (2014) Multi-model results show that limiting total human-induced warming to less than 2 °C relative to the period 1861–1880 with a probability of >66% would require cumulative CO2 emissions from all anthropogenic sources since 1870 to remain below about 2900 Gt(with a range of 2550 to 3150 Gtdepending on non-CO2 drivers). About 1900 Gt had already been emitted by 2011. IPCC (2014)

14. Course Question: • Which role do uncertainties play in (scientific-public-policy…) debates about the „2-degree-limit“?

15. Student groupdiscussion: SourcesofUncertainty Questions: “What are sources of uncertainty relevant for the discussion of the 2-degree target?” „To what extent these uncertainty sources are epistemic and aleatoric, respectively?” “How would you quantify/assess the influence of the respective uncertainty source?” Procedure: Think about the questions individually and take notes (5 min). Build groups of 4-5 (same as in session 1), discuss and synthesise your ideas (up to 15 min). Each group presents their ideas in class (up to 20 min including discussion).

16. Somequestionstothe 2-degree target • What is global average temperature? • What are “preindustrial levels” of temperature? • Why the IPCC chooses the periods 1860-1880 or 1850-1900 as reference periods? • How certain do we know the temperatures in the 19th century? • How much has global temperature increased from 1850 to the present time? • How certain are we about past, present and future anthropogenic CO2 emissions?

17. Uncertainties: What are “preindustrial levels” of temperature? Lüning and Vahrenholt (2017)

18. Somequestionstothe 2-degree target • How do anthropogenic CO2 emissions relate to atmospheric CO2 concentrations (carbon cycle feedbacks)? • How much warming is triggered by the anthropogenic CO2 emissions (climate sensitivity) ? • Is it just CO2? • Whatrole do climate-carboncyclefeedbacksplay? • Whatroledoesclimate internal variabilityplay? • Whatrole do non-anthropogenicforcingsplay?

19. Uncertainties: Carbon budgets AR5 (2014) and SR15 (2018) differ substantially Multi-model results show that limiting total human-induced warming to less than 2 °C relative to the period 1861–1880 with a probability of >66% would require cumulative CO2 emissions from all anthropogenic sources since 1870 to remain below about 2900 Gt(with a range of 2550 to 3150 Gtdepending on non-CO2 drivers). About 1900 Gt had already been emitted by 2011. IPCC (2014)

20. Uncertainties: Carbon budgets AR5 (2014) and SR15 (2018) IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and… TCRE: transientclimateresponse to cumulative carbonemissions(global mean peak surface temperature change per 1000 Gt C emitted as CO2) Rogelj et al. (2018)

21. Some questions to the 2-degree target • What is the acceptable level of climate change? • Howcanweassessthe large varietyofpossibleimpactsofclimatechange on different systemsandregions? • Whataboutbenefits due toclimatechange? • How large are the social costs (due to environmental damages) of CO2 emissions? • How can we estimate future social costs due to climate change? • How large are the abatement costs (due to lowered economic growth)? • What are appropriate discount rates to calculate present values of future monetary losses?

22. How can we assess possible impacts of climate change? • E.g., modellingseaslevelrisefor different scenarios IPCC (2014)

23. How can we assess possible impacts of climate change? E.g., expert judgmentassessments IPCC (2014)

24. Some questions to the 2-degree target • Is the 2-degree target “actionable”? (Geden 2016) • How to “efficiently” communicate scientific uncertainties? • “Efficient” for whom? • Isclearcommunicationofuncertaintiesasrequiredby traditional scientificethics still appropriate? • Shouldclimatescientistshideuncertaintiesto not obstructmitigationpolicies? • Are laymenandpoliticiansabletounderstandscientificstatementsaboutuncertaintiesrelevant tothe 2-degree target?

25. Different disciplinary perspectives on uncertainty Overviewcourse:

26. Isdoubt a badthing? Thoughts on scienceethics

27. Conflict between roles: scientist vs. activist “On the one hand, as scientists we are ethically bound to the scientific method, in effect promising to tell the truth, the whole truth, and nothing but — which means that we must include all the doubts, the caveats, the ifs, ands, and buts. On the other hand, we are not just scientists but human beings as well. And like most people we'd like to see the world a better place, which in this context translates into our working to reduce the risk of potentially disastrous climatic change. To do that we need to get some broadbased support, to capture the public's imagination. That, of course, entails getting loads of media coverage. So we have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we might have.” Schneider, S.H., Discover Magazine, pp. 45–48, October 1989

28. Isdoubt a badthing? Thoughts on scienceethics Accusation: „manufacturinguncertainties“ byinterestgroups Michaels (2008) Oreskes and Conway (2011)

29. Isdoubt a badthing? Mertoniannorms Robert K. Merton 1942: “The ethos of science is that affectively toned complex of values and norms which is held to be binding on the man of science. ” Four major norms: • universalism(validity independent of sociopolitical status of participants) • “communism” (common ownership of scientific goods) • disinterestedness (work for benefit of a common scientific enterprise, rather than for personal gain) • organised skepticism (every scientific claim has to be scrutinized and tested) Merton (1942, 1973)

30. Isdoubt a badthing? Thoughts on scienceethics “It is imperative in science to doubt; it is absolutely necessary, for progress in science, to have uncertainty as a fundamental part of your inner nature. To make progress in understanding, we must remain modest and allow that we do not know. Nothing is certain or proved beyond all doubt. You investigate for curiosity, because it is unknown, not because you know the answer. And as you develop more information in the sciences, it is not that you are finding out the truth, but that you are finding out that this or that is more or less likely.” Richard P. Feynman (2013), The Pleasure of Finding Things Out “Those among us who are unwilling to expose their ideas to the hazard of refutation do not take part in the scientific game.” Karl R. Popper (2002 [1959, 1934], The Logic of Scientific Discovery

31. Homework – 2: Due 13th April • Get together again in the same groups as in session 1 (3rd April). • Formulate a first joint group statement/blog postcovering the following two tasks: • Re-cap your answers to the questions posed for the student group discussion in session 1. Summarize your answers to the questions. • Write a summary or reflection of the discussions and/or content of session 2. • The blog post can, e.g., present ideas and thoughts or give explanations, which you think are necessary to understand the topic. • Write down all usernames of contributing authors at the end of your post • Categorize the blog with the category: ‘Reflections on lecture 2 ’ • Set featured picture: reflections (saved in Media) • This group blog post is in addition to the mandatory individual blog posts that are demanded later during the course. • If you run into any problems, please contact Maike Scheffold (maike.scheffold@uni-hamburg.de) by 11thApril.

32. Steps to post a blog entry • Go tothe Dashboard and Posts. Click on Add New. • Set a title. • Do not useclearnames. Useusernames. • Write yourtext.

33. Steps to post a blog entry 5. Set thecategory: Reflections on lecture 2. 6. Usethe tag: Ideas (Youhavetoclick on add.) 7. Remove sharing check marks. 8. Set thefeaturedimage „Reflections“ byclicking on Set featuredimage

34. Steps to post a blog entry 9. Edit theVisibilityofyourentrytopasswordprotected, enterthe „Master password“ andclick on OK. 10. Check everything. 11. Click on publish.

35. References Feynman, R. P., & Cashman, D. (2013). The pleasure of finding things out. Blackstone Audio, Incorporated. Geden, O. (2016). An actionableclimatetarget. Nature Geoscience, 9(5), 340. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp. IPCC, 2018: Summary for Policymakers. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. World Meteorological Organization, Geneva, Switzerland, 32 pp. Lüning, S., & Vahrenholt, F. (2017). Paleoclimatological context and reference level of the 2° C and 1.5° C Paris Agreement long-term temperature limits. Frontiers in Earth Science, 5, 104. Manabe S, Wetherald RT. The effect of doubling CO2 concentration on the climate of a general. CircModel J AtmosSci1975, 32:3–15. Marcott, S. A., Shakun, J. D., Clark, P. U., and Mix, A. C. (2013). A reconstruction of regional and global temperature for the past 11,300 years. Science 339, 1198–1201. doi: 10.1126/science.1228026 Merton, R. K. (1942). Science and Technology in a Democratic Order, Journal of Legal and Political Sociology 1, 115-126 Merton, R. K. (1973). The sociology of science: Theoretical and empirical investigations. University of Chicago press. Michaels, David (2008). Doubt Is Their Product: How Industry's Assault on Science Threatens Your Health. Oxford University Press. Michaels, D. (2006). Manufactured uncertainty. Annals of the New York Academy of Sciences, 1076(1), 149-162. Michaels, D., & Monforton, C. (2005). Manufacturing uncertainty: contested science and the protection of the public’s health and environment. American journal of public health, 95(S1), S39-S48. Nordhaus, W. D. (1975). Can We Control Carbon Dioxide? IIASA Working, Paper WP-75-63. 1–47. Available online at: http://www.iiasa.ac.at/Admin/PUB/Documents/WP-75-063.pdf Nordhaus, W. D. (1977a). Economic growth and climate: the carbon dioxide problem. Am. Econ. Rev. 67, 341–346. Nordhaus, W. D. (1977b). Strategies for the Control of Carbon Dioxide. Cowles Foundation Discussion Paper No. 443. Cowles Foundation, New Haven, CT. 1–78 Popper, Karl (2002) [1959]. The Logic of Scientific Discovery. Abingdon-on-Thames: Routledge. p. 66

36. References Rogelj, J., D. Shindell, K. Jiang, S. Fifita, P. Forster, V. Ginzburg, C. Handa, H. Kheshgi, S. Kobayashi, E. Kriegler, L. Mundaca, R. Séférian, and M.V. Vilarino, 2018: Mitigation Pathways Compatible with 1.5°C in the Context of Sustainable Development. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. Oreskes, N., & Conway, E. M. (2011). Merchants of doubt: How a handful of scientists obscured the truth on issues from tobacco smoke to global warming. Bloomsbury Publishing USA. Ward, B., & Dubos, R. (1972). Only one earth. The care and maintenance of a small planet. Harmondsworth: Penguin Books Ltd. (unofficial report, commissioned by the Secretary-General of the United Nations Conference on the Human Environment) Internet: European Council, (1996). Community Strategy on Climate Change - Council Conclusions. Available online at: http://europa.eu/rapid/press-release_PRES-96-188_en.htm?locale=en United Nations (1992). https://unfccc.int/resource/docs/convkp/conveng.pdf United Nations (2009). https://unfccc.int/resource/docs/2009/cop15/eng/l07.pdf United Nations (2015). https://unfccc.int/sites/default/files/english_paris_agreement.pdf

37. Additional slides

38. Scenario diversity AR5 IPCC (2014)

39. Aleatoricandepistemicuncertainties Aleatoric uncertainty Aleatoric uncertainty is also known as statistical uncertainty, and is representative of unknowns that differ each time we run the same experiment and cannot be deterministically described. The argument here is obviously in the definition of "cannot". Just because we cannot measure sufficiently with our currently available measurement devices does not preclude necessarily the existence of such information, which would move this uncertainty into the below category Epistemic uncertainty Epistemic uncertainty is also known as systematic uncertainty, and is due to things one could in principle know but doesn't in practice. This may be because a measurement is not accurate, because the model neglects certain effects, or because particular data has been deliberately hidden. Adaptedfrom https://en.wikipedia.org/wiki/Uncertainty_quantification

40. The course blog Wehave a virtual study and discussion space: https://uncertain2degrees.blogs.uni-hamburg.de/ The blogworkspace will be used to: Provideyou with all information on Course idea and structure Rules and procedures Homework and lecture slides Blog about Ideas and toughts Your experiences with your role-plays Document The arguments of the discussions The perspective ouf your respective role Inform interested parties about our work (laterin theyear) The blog is currently partly public. For now, we will keep our content password secured. The blog is work in progress! (be gentle on us ;) ) The blog is your arena of expression and documentation. Here, you find all relevant information. Please make sure that you check-out and work with the blog on a regular basis.

41. Homework # 1 • Get to know the blog, its features and go through all information given on the course. Therefore, • Fill in your university email address, your name and your username in the list provided at the end of the lecture. Set your username as follows: • Lisa Baume lisbau (the first 3 letters of your first and 3 of your second name) • Manfred Arm manarm • We will send you an invitation to that email address within the next day. • Accept the invitation to the blog (click on the Invitation Accepted link). • Create a new WordPress-account with the username you set before in the list. If this username is not working, please try a different version, e.g. lisbau2018. • If you run into any problems or changed the username, please contact Maike Scheffold (maike.scheffold@uni-hamburg.de.) Due: 9th April