Scenarios compatible with the LTGG considered in the IPCC 2018-19 special reports

First meeting of the Structured Expert Dialogue of the second periodic reviewTheme 1 - November 2020Presentation team: Kate Calvin (Coordinating Lead Author SRCCL, USA)Mikiko Kainuma (Lead Author SR1.5, Japan)Joeri Rogelj (Coordinating Lead Author SR1.5, Belgium)Roberto Schaeffer (Review Editor SR1.5, Brazil)

The talk covers:

Emissions aspects of scenarios compatible with LTGG• Net zero CO2 and net zero greenhouse gas emissions • Comparability between scenarios and inventories

Carbon-dioxide removal aspects• Trade-off between near term reductions and reliance

on carbon-dioxide removal• Integrated view on carbon-dioxide removal: options,

limitations, and side-effects

Global CO2 emissions are reduced to net zero and non-CO2 emissions are strongly reduced as well for limiting global warming to 1.5°C

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Pathways limiting warming below 2°C

Timing of net zero CO2Pathways with higher overshoot of 1.5°CPathways with no or limited overshoot of 1.5°C

Global CO2 emissions Global non-CO2 emissions

The timing and the temperature outcome is different for net zero CO2 or net zero total greenhouse gas (GHG) emissions

2000 2020 2040 2060 2080 2100

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850-

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median temperature change: 1.5°C low/no overshoot17-83 percentile range across scenarios

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net GHG emissionsnet CO2 emissions

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net-zero CO2around 2050 (2046–2055)

net-zero greenhouse gases (GHG) around two decades later 2067 (2061, 2084)

Projected global warming for pathways with no or limited overshoot of 1.5°C

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net-zero CO2around 2050 (2046–2055)≈ time of peak temperature

net-zero greenhouse gases (GHG) around two decades later 2067 (2061, 2084)≈ temperature has peaked and starts to decline gradually

The timing and the temperature outcome is different for net zero CO2 or net zero total greenhouse gas (GHG) emissions

Projected global warming for pathways with no or limited overshoot of 1.5°C

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2000 2020 2040 2060 2080 2100Year

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0

20

40

emis

sion

s (G

t CO

2 or C

O2-e

q / y

r )

net CO2 emissionsgross CO2 emissionstotal CDR

Carbon-dioxide removal (CDR) is necessary for net zero CO2 emissionsSo

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Mitigation pathways rely on CDR

• to achieve net-zero CO2(compensate for residual CO2and stabilize warming)

• to achieve net-negative CO2emissions afterwards(achieve temperature decline)

2000 2020 2040 2060 2080 2100Year

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0

20

40

emis

sion

s (G

t CO

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O2-e

q / y

r )

net GHG emissionsgross GHG emissionstotal CDR

Carbon-dioxide removal (CDR) is necessary for net zero greenhouse gas (GHG) emissions

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Mitigation pathways rely on CDR

• to achieve net-zero GHG(compensate for residual CO2and hard-to-abate residual non-CO2 emissions)

National GHG inventories and global pathways define the anthropogenic land flux differently thus requiring special attention when setting targets

Global pathways

National GHG inventories

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Carbon-dioxide removal (CDR) plays a role in achieving both net zero CO2 and net zero greenhouse gas emissions

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but timing and scale depends:• on stringency of gross emissions reduction over near term• on mitigation portfolio and strategy, including desired mix

of CDR technologies (AFOLU, BECCS, DAC, other …)• on desired rate of temperature decline after the peak

(net negative emissions)

An integrated view on carbon-dioxide removal (CDR): various optionsSo

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CDR options vary in:• cost • potential• side-effects

Risks of “overshooting”: • higher temperature resulting in increased

climate risks (talk 3) • risk of failure to reverse warming after

overshoot because: • exceeding global warming limits can

weaken or reverse land-based carbon storage

• limits to the sustainable CDR potential

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Side-effects and synergies: land requirements, food, water, and sustainable development impacts depend on scale of deployment & socioeconomic context

Suitable & sustainable national level of bioenergy depends on local aspects

Response options and their contribution to mitigation, adaptation, and combating desertification, land degradation, and enhancing food security

Conclusions

• Various scenarios compatible with the LTGG do exist

• These different scenarios have implications for the timing of net zero CO2 and net zero greenhouse gases, with the latter coming later, and for the resulting temperature outcomes

• National GHG inventories and global pathways define the anthropogenic land flux differently, thus requiring special attention when setting targets

• Carbon-dioxide removal (CDR) plays a role in achieving both net zero CO2and net zero greenhouse gas emissions

• But there are trade-offs between near term reductions and CDR reliance

• Land requirements, food, water, and sustainable development impacts of land-based CDR depend on the scale of deployment & socioeconomic context