Well below 2 °C: Mitigation strategies for avoiding dangerous to catastrophic climate changes
Edited by Susan Solomon, Massachusetts Institute of Technology, Cambridge, MA, and approved August 11, 2017 (received for review November 9, 2016)
Abstract
The historic Paris Agreement calls for limiting global temperature rise to “well below 2 °C.” Because of uncertainties in emission scenarios, climate, and carbon cycle feedback, we interpret the Paris Agreement in terms of three climate risk categories and bring in considerations of low-probability (5%) high-impact (LPHI) warming in addition to the central (∼50% probability) value. The current risk category of dangerous warming is extended to more categories, which are defined by us here as follows: >1.5 °C as dangerous; >3 °C as catastrophic; and >5 °C as unknown, implying beyond catastrophic, including existential threats. With unchecked emissions, the central warming can reach the dangerous level within three decades, with the LPHI warming becoming catastrophic by 2050. We outline a three-lever strategy to limit the central warming below the dangerous level and the LPHI below the catastrophic level, both in the near term (<2050) and in the long term (2100): the carbon neutral (CN) lever to achieve zero net emissions of CO2, the super pollutant (SP) lever to mitigate short-lived climate pollutants, and the carbon extraction and sequestration (CES) lever to thin the atmospheric CO2 blanket. Pulling on both CN and SP levers and bending the emissions curve by 2020 can keep the central warming below dangerous levels. To limit the LPHI warming below dangerous levels, the CES lever must be pulled as well to extract as much as 1 trillion tons of CO2 before 2100 to both limit the preindustrial to 2100 cumulative net CO2 emissions to 2.2 trillion tons and bend the warming curve to a cooling trend.
Supporting Information
Appendix (PDF)
- Download
- 759.90 KB
References
1
; UNFCCC, Synthesis report on the aggregate effect of the intended nationally determined contributions. Available at unfccc.int/resource/docs/2015/cop21/eng/07.pdf. Accessed August 23, 2017. (2015).
2
; International Energy Agency World Energy Outlook 2016 (International Energy Agency, Paris, 2016).
3
C Figueres, et al., Three years to safeguard our climate. Nature 546, 593–595 (2017).
4
L Clarke, et al., Assessing transformation pathways. Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, eds O Edenhofer, et al. (Cambridge Univ Press, Cambridge, UK, 2014).
5
DG Victor, CF Kennel, Climate policy: Ditch the 2 °C warming goal. Nature 514, 30–31 (2014).
6
BM Sanderson, et al., Community climate simulations to assess avoided impacts in 1.5 °C and 2 °C futures. Earth Syst Dynam Discuss. Available at https://doi.org/10.5194/esd-2017-42. Accessed August 23, 2017. (2017).
7
V Ramanathan, Y Xu, The Copenhagen Accord for limiting global warming: criteria, constraints, and available avenues. Proc Natl Acad Sci USA 107, 8055–8062 (2010).
8
Y Xu, D Zaelke, GJM Velders, V Ramanathan, The role of HFCs in mitigating 21st century climate change. Atmos Chem Phys 13, 6083–6089 (2013).
9
A Hu, Y Xu, C Tebaldi, WM Washington, V Ramanathan, Mitigation of short-lived climate pollutants slows sea-level rise. Nat Clim Chang 3, 730–734 (2013).
10
Y Xu, L Lin, Pattern scaling based projections for precipitation and potential evapotranspiration: Sensitivity to composition of GHGs and aerosols forcing. Clim Change 140, 635–647 (2017).
11
G Flato, et al., Evaluation of climate models. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, eds TF Stocker, et al. (Cambridge Univ Press, Cambridge, UK, 2013).
12
S Hsiang, et al., Estimating economic damage from climate change in the United States. Science 356, 1362–1369 (2017).
13
M Collins, et al., Long-term climate change: Projections, commitments and irreversibility. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, eds TF Stocker, et al. (Cambridge Univ Press, Cambridge, UK, 2013).
14
GH Roe, MB Baker, Why is climate sensitivity so unpredictable? Science 318, 629–632 (2007).
15
K Pistone, I Eisenman, V Ramanathan, Observational determination of albedo decrease caused by vanishing Arctic sea ice. Proc Natl Acad Sci USA 111, 3322–3326 (2014).
16
FA-M Bender, V Ramanathan, G Tselioudis, Changes in extratropical storm track cloudiness 1983–2008: Observational support for a poleward shift. Clim Dyn 38, 2037–2053 (2012).
17
JR Norris, et al., Evidence for climate change in the satellite cloud record. Nature 536, 72–75 (2016).
18
I Tan, T Storelvmo, MD Zelinka, Observational constraints on mixed-phase clouds imply higher climate sensitivity. Science 352, 224–227 (2016).
19
CE Forest, PH Stone, AP Sokolov, MR Allen, MD Webster, Quantifying uncertainties in climate system properties with the use of recent climate observations. Science 295, 113–117 (2002).
20
P Ciais, et al., Carbon and other biogeochemical cycles. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, eds TF Stocker, et al. (Cambridge Univ Press, Cambridge, UK, 2013).
21
JT Randerson, et al., Multicentury changes in ocean and land contributions to the climate-carbon feedback. Global Biogeochem Cycles 29, 744–759 (2015).
22
TML Wigley, SCB Raper, Interpretation of high projections for global-mean warming. Science 293, 451–454 (2001).
23
R Knutti, TF Stocker, F Joos, G-K Plattner, Constraints on radiative forcing and future climate change from observations and climate model ensembles. Nature 416, 719–723 (2002).
24
M Webster, et al., Uncertainty analysis of climate change and policy response. Clim Change 61, 295–320 (2003).
25
GH Roe, Y Bauman, Climate sensitivity: Should the climate tail wag the policy dog? Clim Change 117, 647–662 (2013).
26
EJ Rohling, et al., High rates of sea-level rise during the last interglacial period. Nat Geosci 1, 38–42 (2008).
27
HD Matthews, S Solomon, Irreversible does not mean unavoidable. Science 340, 438–439 (2013).
28
A Grübler, N Nakicenovic, DG Victor, Dynamics of energy technologies and global change. Energy Policy 27, 247–280 (1999).
29
; IPCC, Summary for policymakers. Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, eds O Edenhofer, et al. (Cambridge Univ Press, Cambridge, UK, 2014).
30
M Meinshausen, et al., Greenhouse-gas emission targets for limiting global warming to 2 degrees C. Nature 458, 1158–1162 (2009).
31
; WHO, Burden of disease from the joint effects of Household and Ambient Air Pollution for 2012. Available at www.who.int/phe/health_topics/outdoorair/databases/AP_jointeffect_BoD_results_Nov2016.pdf. Accessed August 23, 2017. (2016).
32
D Shindell, et al., Simultaneously mitigating near-term climate change and improving human health and food security. Science 335, 183–189 (2012).
33
J Rogelj, et al., Disentangling the effects of CO2 and short-lived climate forcer mitigation. Proc Natl Acad Sci USA 111, 16325–16330 (2014).
34
; UNEP and WMO, Integrated assessment of black carbon and tropospheric ozone. Available at https://wedocs.unep.org/rest/bitstreams/12809/retrieve. Accessed August 23, 2017. (2011).
35
; United Nations, Kigali amendment. Available at https://treaties.un.org/doc/Publication/CN/2016/CN.872.2016-Eng.pdf. Accessed August 23, 2017. (2016).
36
V Ramanathan, Greenhouse effect due to chlorofluorocarbons: Climatic implications. Science 190, 50–52 (1975).
37
; California Legislative Information, SB-1383 Short-lived climate pollutants: Methane emissions: dairy and livestock: organic waste: landfills. Available at https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=201520160SB1383. Accessed August 23, 2017. (2016).
38
D Archer, V Brovkin, The millennial atmospheric lifetime of anthropogenic CO2. Clim Change 90, 283–297 (2008).
39
; IPCC IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation. Prepared by Working Group III of the Intergovernmental Panel on Climate Change, eds O Edenhofer, et al. (Cambridge Univ Press, Cambridge, UK, 2011).
40
V Ramanathan, et al., Bending the curve: Ten scalable solutions for carbon neutrality and climate stability. Collabra: Psychology 2, 15 (2016).
41
LG Streiff, V Ramanathan, Under 2 °C living laboratories. Urban Clim, July 12, 2017).
42
D Tilman, J Hill, C Lehman, Carbon-negative biofuels from low-input high-diversity grassland biomass. Science 314, 1598–1600 (2006).
43
D Woolf, JE Amonette, FA Street-Perrott, J Lehmann, S Joseph, Sustainable biochar to mitigate global climate change. Nat Commun 1, 56 (2010).
44
R Lal, Enhancing crop yields in the developing countries through restoration of the soil organic carbon pool in agricultural lands. Land Degrad Dev 17, 197–209 (2006).
45
JB Smith, et al., Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change (IPCC) “reasons for concern”. Proc Natl Acad Sci USA 106, 4133–4137 (2009).
46
JB Smith, et al., Vulnerability to climate change and reasons for concern: A synthesis. Climate Change 2001: Impacts, Adaptation, and VulnerabilityMcCarthy JJCanziani OFLeary NADokken DJWhite KS (IPCC, Cambridge Univ Press, Cambridge, UK), pp. 913–967 (2001).
47
BC O’Neill, et al., IPCC reasons for concern regarding climate change risks. Nat Clim Chang 7, 28–37 (2017).
48
TM Lenton, et al., Tipping elements in the Earth’s climate system. Proc Natl Acad Sci USA 105, 1786–1793 (2008).
49
E Kopits, E Marten, E Wolverton, Incorporating ‘catastrophic’ climate change into policy analysis. Clim Policy 14, 637–664 (2014).
50
SC Sherwood, M Huber, An adaptability limit to climate change due to heat stress. Proc Natl Acad Sci USA 107, 9552–9555 (2010).
51
C Mora, et al., Global risk of deadly heat. Nat Clim Chang 7, 501–506 (2017).
52
; WMO, Global Climate in 2011–2015. Available at https://public.wmo.int/en/resources/library/global-climate-2011%E2%80%932015. Accessed August 23, 2017. (2016).
53
D Mitchell, et al., Attributing human mortality during extreme heat waves to anthropogenic climate change. Environ Res Lett 11, 074006 (2016).
54
ME Mann, Defining dangerous anthropogenic interference. Proc Natl Acad Sci USA 106, 4065–4066 (2009).
55
BP Dasgupta, V Ramanathan, Pursuit of the common good. Science 345, 1457–1458 (2014).
56
; Pontifical Academy of Sciences, Final Statement. PAS-PASS Workshop, Feb 27–March 1, 2017. Available at www.pas.va/content/accademia/en/events/2017/extinction/statement.html. Accessed August 23, 2017. (2017).
57
AD Barnosky Dodging Extinction: Power, Food, Money, and the Future of Life on Earth (Univ of California Press, Berkeley, CA, 2014).
58
NS Diffenbaugh, CB Field, Changes in ecologically critical terrestrial climate conditions. Science 341, 486–492 (2013).
Information & Authors
Information
Published in
Cover image: Pictured are brown bears (Ursus arctos middendorffi) behind an elderberry shrub on Kodiak Island, Alaska. William W. Deacy et al. found that elderberries on Kodiak Island ripened earlier than usual during years with warm springs. In response, brown bears left active salmon spawning streams to forage for berries on neighboring hillsides. According to the authors, the change in the bears' feeding habit might disrupt the fertilization of terrestrial ecosystems that usually accompanies salmon predation by bears, demonstrating how climate change can disrupt the timing of prey availability. See the article by Deacy et al. on pages 10432–10437. Image courtesy of Lisa Hupp, US Fish and Wildlife Service.
Classifications
Copyright
Copyright © 2017 the Author(s). Published by PNAS. This is an open access article distributed under the PNAS license.
Submission history
Published online: September 14, 2017
Published in issue: September 26, 2017
Keywords
Notes
This article is a PNAS Direct Submission.
Authors
Competing Interests
The authors declare no conflict of interest.
Metrics & Citations
Metrics
Citation statements
Altmetrics
Citations
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.
Cited by
Loading...
View Options
View options
PDF format
Download this article as a PDF file
DOWNLOAD PDFLogin options
Check if you have access through your login credentials or your institution to get full access on this article.
Personal login Institutional LoginRecommend to a librarian
Recommend PNAS to a LibrarianPurchase options
Purchase this article to access the full text.