Scenarios assessed by the IPCC

Scenarios assessed by the IPCC
Glen Peters (CICERO Center for International Climate Research, Oslo, Norway)
Workshop on Cost of Carbon (Norwegian Environment Agency, 15/05/2019)

• Interpreting the Paris Agreement, or not?
• What are the key characteristics of 1.5°C & 2°C pathways?
• Is the devil in the details?
• Discussion…
Overview

• Article 2: “Holding the increase … to well below 2°C …
and pursuing efforts to limit … to 1.5°C …”
• Article 4: “global peaking … as soon as possible …
undertake rapid reductions … achieve a balance between
… sources and … sinks of GHGs … in the second half
of this century”
The Paris Agreement (goals)
Source: Peters (2017)

• UNFCCC (1992): Avoid dangerous climate change
• Copenhagen (2009): “below 2°C” (consider 1.5°C by 2015)
• IPCC AR5 (2013/14): 66% probability below 2°C (~RCP2.6)
• Paris (2015): “well below 2°C…pursuing…1.5°C”
– “balance [in GHGs between 2050-2100], [SD & eradicate poverty]”
• IPCC SR15: “below 1.5°C in 2100 with [no or low overshoot]”
– 45% decline in emissions by 2030 (from 2010), net-zero ~2050
• “Activists”: Generally, below 1.5°C without negative emissions
The changing goal posts

The Paris text “well below 2°C…pursuing…1.5°C” seems to say between 1.5°C and 2°C, but ambiguous time period…
Data: IAMC 1.5°C Scenario Explorer (hosted by IIASA)
The Paris temperature window
IPCC AR5
IPCC SR15

“Achieve a balance between…sources and…sinks of GHGs in the second half of the century” is rather ambitious!
Much more consistent with 1.5°C. Many definitional issues, though, one can assume knowledge from scenarios.
The GHG balance 2050 to 2100

The Paris Agreement (concept)
Nationally
Determined
Contributions
(NDCs)
Global
Stocktake
Raise
ambition
(currently on track
for 3°C in 2100)
(strengthen NDCs)
(new)
Repeat process
every five years

The Paris Agreement states its goal as “well below 2°C”, but Paris is more about the direction of travel…
Emission pledges are not sufficient, what is the process to raise ambition?
Source: Task Force on Climate-Related Financial Disclosures (TCFD)
It is the direction that matters

There is a trade-off between mitigation & adaptation, but the time-scales are decades different…
Though, there are some short-term benefits of mitigation as well, reduced local air pollution, new jobs, etc
Source: Rogelj et al 2018; Riahi et al. 2016; IIASA SSP Database; NASA GISS
A lot of pain, not much gain?
Paris pledges
Paris goal
CO2
Benefits
°C
Little gain

• It is framed as “cost effective” (“well below 2°C”)
– Is cost-benefit analysis even relevant?
• Reality: raise ambition, ensure sustainable development
– How far to raise ambition while allowing SD & eradicate poverty?
– Keeps cost-benefit analysis relevant? Global or regional?
• Moot? Countries will align somewhat along ‘self interest’?
– Countries are not global optimisers over 100 year time scale…
The Paris Agreement

Key (IAM) characteristics of 1.5°C & 2°C

There are now a new set of scenarios consistent with 1.5°C, in addition to existing 2°+C scenarios
IPCC Special Report on 1.5°C

There are 400+ scenarios across 13 models, but the model distribution is far from uniform (beware of biases)
IPCC Special Report on 1.5°C

Without climate policy, temperature >3°C
We live in a world with climate policy, and most studies suggest current policies lead to about 3°C in 2100
There is a large range of baseline scenarios, we do not know the “baseline” world in the future…
Paris Agreement
pushes emissions down

For 2°C, 25% reduction by 2030, net-zero around 2075, around 10GtCO2 (gross) negative emissions by 2100
2°C pathways require a radical change
Nationally Determined Contributions
(emission pledges)

For 1.5°C, 50% reduction by 2030, net-zero by 2050, around 15GtCO2 (gross) negative emissions by 2100
1.5°C pathways are 2°C plus more
Nationally Determined Contributions
(emission pledges)

What are the “key characteristics” of 1.5°C? These are stylised, but based on average scenario outputs.
CO2 Emissions in a 1.5°C world
This is not an emission,
but to give an idea of
the scale of CCS

What are the “key characteristics” of 1.5°C? These are stylised, but based on average scenario outputs.
Energy system in a 1.5°C world
Fossils
Non-fossils
Bioenergy

The devil is in the details…
Multiple IAMs, multiple stories

There are many ways to get to 2°C, depending on socioeconomic and modelling assumptions
All 2°C scenarios require rapid decarbonization, zero emissions around 2070, and negative emissions thereafter
Source: IIASA SSP Database
Carbon dioxide pathways to 2°C

While there is little flexibility in the carbon dioxide pathways to 2°C, there is a big variation in energy consumption
Here are 18 scenarios consistent with 2°C, the “missing scenarios” are assumptions that could not keep below 2°C
SSPs represent different socioeconomic pathways (five in total), different models are abbreviated in brackets)
Energy system pathways to 2°C

… and very different energy mixes. It is possible to have high energy consumption with no fossil fuels, low energy
consumption with lots of fossil fuels, and everything in between. There is no single pathway to 2100.

At the detailed level, there are many different energy systems that can be consistent with 2°C. E.g., it is not possible
to categorically say 2°C is consistent with low fossil fuel consumption, as it depends on CCS assumptions

The carbon budget (cumulative emissions) can be defined in several ways & varies by model (all using MAGICC)
A key factor in determined the carbon budget is the non-CO2, which varies by model…
Source: Peters (2018)
Carbon budgets (SSP 1.5°C scenarios)
Carbon budgets

Carbon prices vary considerably by model, & reach values that are hard to interpret.
Fossil emissions will be low & tax payments low, but negative emissions high and rebates high (5+% global GDP)…
Carbon prices

• Different types of models
– optimization – simulation; myopic – foresight; solution method;
input assumptions (technology costs); discounting rates; …
– No one seems to know what drives different IAM outputs…
• Robust conclusions from models
– Fossil fuels out, non-fossils in, CO2 removal needed, etc
– Delay is costly, no technology winners, trade-offs – synergies, …
• Enough for policy? Academics can argue the details?
Model variations

• IAMs (& scenarios) have a particular way of addressing
the policy problem (eg hard target with optimization)
– This frames much of the policy discussion…
– Have the IAMs framed the problem in a useful way?
– Can IAMs frame the problem differently (e.g., raised ambition?)
• IAMs give similar key characteristics for 1.5°C and 2°C,
but do the details matter?
– Does it matter if wind or solar dominate in 2050?
– Does CO2 removal require incentives (now)?
Summary

Peters_Glen
cicero.oslo.no
cicerosenterforklimaforskning
glen.peters@cicero.oslo.no
Glen Peters

(Selected) key issues with modelling

• Understanding model diversity
– Optimization vs simulation
– Myopic versus perfect foresight
– The role of discount rates in results
– Policy implementation (fragmentation or uniform)
• Model set up
– Limited resource (carbon budget), increasing carbon tax
– Leads to overshoot scenario
(Selected) key issues

Emission scenarios are used to explore the consequences of key uncertainties (climate, technical, social, political)
Scenarios are not projections or predictions, but tools to assess risks…
Source: Riahi et al. 2016; IIASA SSP Database; Rogelj et al (2018); Global Carbon Budget 2017
Scenarios used to explore uncertainties

The SSPs offer a way to structure assumptions about socio-economic futures, but will most use SSP2?
Source: Riahi et al. 2016; IIASA SSP Database; Rogelj et al (2018); Global Carbon Budget 2017
Shared Socio-Economic Pathways (SSPs)

How do I interpret model ensembles?
In most 1.5°C or 2°C scenarios, coal goes off a cliff. The only life for coal is if CCS becomes a (cheap) reality.
Coal goes off a cliff…

In most 2°C scenarios there is a ‘supply gap’, requiring new investment (but less than >2°C)
In 1.5°C scenarios the future is more complex, and oil often lingers into the future.
Oil has a complex future…

Gas could double or it could halve. It is up to the fossil industry to make the case for gas…
Gas is anyone’s guess…

Solar appears to dominate, but the median values are similar (in 2100). One model (REMIND) completely dominates
the solar high-end scenarios…
Solar and wind grow rapidly

Very little growth above the baseline scenario, except in the models GCAM and MESSAGE
Nuclear

Biomass grows (no pun) strongly in most scenarios, mainly for use with CCS (negative emissions)
However, even if negative emissions excluded, then biomass often used elsewhere.
Biomass

Almost independent of temperature level, CCS is used at scale (biomass, fossil, industry)
To get 10GtCO2 CCS in 2050 requires about a new facility (1MtCO2) every day until 2050…
Carbon Capture & Storage (CCS)

Bioenergy with CCS removes around 10GtCO2 per year from 2050-2100, but requires a lot of land.
Land use impacts are significant, around 400Mha (~India), but can be over 1000Mha.
CO2 removal (bioenergy with CCS)

Afforestation remove around 5GtCO2 per year from 2050-2100, but requires a lot of land.
Biomass with CCS tends to remove more CO2 for less land (as the land is reused).
CO2 removal (land use)

Scenarios are starting to include Direct Air Capture (DAC). Expensive, but potential for air-to-fuels makes attractive?
Direct Air Capture (DAC)

• Scenarios indicate a large need for CCS & CDR
• Opportunities, if a market is developed
• Carbon Capture & Storage
– Industry, biomass, and maybe fossil fuels (gas?)
• Carbon dioxide removal has a few exciting pathways
– Direct Air Capture
– Air to Fuels
– …
Carbon Capture & Storage / Removal

Scenarios assessed by the IPCC

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