Temperature targets, carbon budgets, emission pathways, and negative emissions

Transcription

1 Temperature targets, carbon budgets, emission pathways, and negative emissions Sivan Kartha Stockholm Environment Institute Kate Dooley The University of Melbourne Looking ahead: Land use and Forests in the Paris Agreement, real world implications of negative emissions and Bioenergy CCS 12 May 2016, Brussels

2 The Paris Agreement temperature goal(s) holding the increase in the global average temperature to well below 2 C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 C above pre-industrial levels [Paris Agreement, Art. 2] reach global peaking of greenhouse gas emissions as soon as possible, recognizing that peaking will take longer for developing country Parties, and achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century [Paris Agreement, Art. 4] 2

3 Sea Level Rise Sea Level, m Pliocene 3 Myr ago Eocene 40 Myr ago Global T Change, C Today IPCC estimate for Last Glacial Maximum 20 kyr ago David Archer, Understanding the Forecast, presented 2012

4 Sea Level Rise Sea Level, m Pliocene 3 Myr ago Eocene 40 Myr ago Global T Change, C Today Eventual Sea Level Rise? Last Glacial Maximum 20 kyr ago David Archer, Understanding the Forecast, presented 2012

5 Sea level reached +6-9 meters in the Eemian, a time that we have concluded was probably no more than a few tenths of a degree warmer than today. We observe accelerating mass losses from the Greenland and Antarctic ice sheets, and we have identified amplifying feedbacks that will increase the rates of change. 5

6 Temperature rise depends on cumulative historical emissions IPCC AR5, WG1 SPM, p. 28 6

7 The budget depends on the chosen temperature threshold and risk of exceeding it IPCC AR5, Synthesis Report, Table C (66% chance): 400 GtCO 2 (550 GtCO2 for 50% chance of 1.5 C) 2 C (66% chance): 1,000 GtCO 2 (Caution: these budgets are from 2011 onward. Subtract ~200 GtCO2 already spent over last five years.) 7

8 The temp rise just depends on the budget used, and not (too much) on the pathway Negative emissions GtCO2 Each pathway is ~1,000 GtCO2 by (But some with overshoot and negative emissions.) IPCC AR5, WG3, Ch. 12, Fig

9 But, there is major uncertainty Coul 2 C (66% chance): 750-1,400 GtCO 2 Budget could be significantly more, or could be significantly less. 9

10 UNFCCC Secretariat assessment of the INDCs ~present Historical Emissions Remainder in 2025 In 2030 Historical Emissions INDCs Remainder Approximately half of the remaining available 2 C budget would be consumed by 2025, and three-quarters would be consumed by Annual emissions would still be rising. UNFCCC Secretariat, 2 May

11 UNFCCC Secretariat assessment of the INDCs ~present Historical Emissions Remainder in 2025 In 2030 Historical Emissions INDCs When preparing this document, no scenarios were available in the scientific literature of limiting or returning global average temperature rise to below 1.5 C by 2100 considering global emission levels in 2030 resulting from the implementation of the INDCs. UNFCCC Secretariat, 2 May

12 As emissions grow, the budget is depleted International Energy Agency, 2015 Special Report on Energy and Climate Change 12

13 Carbon emission pathways for 2 C & 1.5 C Rogelj et al., 2015, Nature Climate Change Based on 200 MESSAGE and REMIND scenarios 13

14 While most 2 C-consistent scenarios thus also strongly rely on CDR, examples with a significantly lower or even zero contribution of negative emissions are available in the literature (albeit at substantially higher costs). (Rogelj, 2015) Large-scale application of BECCS or alternative CDR technologies in the second half of the twenty-first century seem indispensable for 1.5 C scenarios, as temperatures in such scenarios do not have only to stabilize but also to peak and decline. If CDR technologies such as BECCS do not become available on a large scale and at societally acceptable costs, models are not able to limit cumulative emissions to a level that would restrict warming to 1.5 C in (Rogelj, 2015) 14

15 Negative emissions in 2 C & 1.5 C pathways Pathway negative emissions 0 to ~900 GtCO2 450 to 1000 GtCO2 Rogelj et al., 2015, Nature Climate Change 15

16 BECCS requirements in scenarios in full IPCC AR5 database But many 2 C scenarios with > 1000 GtCO2 of BECCS Roughly 10% of 2 C scenarios with no BECCS Wiltshire & Davies,

17 Summary The carbon budget is: A lot smaller for 1.5 C than for 2 C (400 vs 1000 GtCO2) Quite uncertain, it could be smaller or larger than the median estimates, by a wide margin. Depends in part on how rapidly non-co2 emissions are reduced. Estimated without taking into account irreversible effects like forest dieback, permafrost carbon release, methane hydrate outgassing, ice sheet decline. These effects are more likely the more the budget is exceeded (i.e., the greater the overshoot). 17

18 Summary (continued) The modeled 1.5 C and 2 C pathways: Tend to overshoot their budget, in many cases by a large amount (emissions much more than double the budget). Instead of rapid near-term reductions, many pathways rely on slower near-term reductions and negative emissions in the longer-term. Rely on land-based sinks and BECCS for negative emissions to pay back the overshoot. Do not limit negative emissions by realistic biophysical or socio-economic constraints. Some models use fantastic amounts of negative emissions. See Kate s presentation for discussion of realistic limits. 18

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