The Implications of Deep
Mitigation Pathways
23RD AIM INTERNATIONAL WORKSHOP
November 2017
Tsukuba, JAPANScience Questions

What are the implications of mitigating
to 1.5°C on the economy, energy,agriculture, and land use sectors?
How sensitive are our results tochanges in underlying assumptions?

Approach
Model:
Global Change Assessment
Model (version 4.3), with theHector climate emulator

Target:Limiting 2100 temperature to1.5°C
Overshoot is allowed.

GCAM

The Global Change Assessment Model (GCAM)
32 Region Energy/Economy Model

GCAM is a global complex, multi-scale,human-Earth system model
GCAM links Economic, Energy, Landuse, and Climate systems
Typically used to examine the effect oftechnology and policy on the economy,energy system, agriculture and land-use,and climate
Technology-rich model

283 Agriculture and Land Use Model

Emissions of 24 greenhouse gases andshort-lived species: CO2, CH4, N2O,
halocarbons, carbonaceous aerosols,
reactive gases, sulfur dioxide.
Runs through 2100 in 5-year time-steps.
Open source:
https://github.com/jgcri/gcam-core
Documentation available at:
http://jgcri.github.io/gcam-doc/

Note: this research uses the GCAM v4.3 releaseScience Questions
What are the implications of mitigating to 1.5°C
on the economy, energy, agriculture, and land usesectors?
How sensitive are our results to changes inunderlying assumptions?

Limiting temperature to 1.5C requires a significant
decrease in emissions.
Global Mean Temperature Rise
Reference
1.5°C

Global GHG Emissions

Global energy system CO2 emissions are
net negative beginning in 2050.
Global GHG Emissions

Carbon Price

Limiting temperature to 1.5°C requires asubstantial transition in the energy system
Global Primary Energy Consumption

X-foldincrease insolar
X nuclear
reactors*** bioCCS

Phase outof coal by2***

Producing this bioenergy requires x% ofland to be devoted to bioenergy in 2100.
Global Land Cover

X% decline
in forestcover
X-foldincrease incrop priceScience Questions
What are the implications of mitigating to 1.5°C
on the economy, energy, agriculture, and land use
sectors?
How sensitive are our results to changes inunderlying assumptions?

We varied five different assumptions within
GCAM to test sensitivity of reaching 1.5°C.
Socioeconomics (SSP1, SSP2, SSP3)

3

Land Policy (None, Protect, Afforest, 50% Afforest, Bio Tax) x 5
Bioenergy Availability (No constraint, 0 EJ/yr, 100 EJ/yr,200 EJ/yr)

x4

Agricultural Productivity (Reference, Low)

x2

Climate Target (1.5°C, 1.9 W/m2)

x2
240

Of the 240 simulations attempted, 76 were successful
Total Radiative Forcing

The more bio,the higherovershootGlobal Mean Temperature Rise

Withoutbioenergy,
1.5C isn’t
feasibleLimiting bioenergy results in more rapidemissions reductions and higher carbon prices.
Energy CO2 Emissions

Carbon PriceMajor Caveats
Limited sensitivity experiment
We only varied five assumptions:socioeconomics, land policy, bioenergy
availability, agricultural productivity,
climate target.
There are many other uncertainties thatshould be explored (e.g., technology cost,near-term climate policy).

Model choice
We are only using a single IAM.
We are not capturing structural
uncertainty at all.

Global Mean Temperature Rise

Major Caveats (continued)
Feasibility
We have defined feasibility in a technicalmanner. We haven’t examined economic
or political feasibility.
In some ways, we are probably too
optimistic. In other ways, too pessimistic.

Definition of 1.5 degrees
We only looked at 1.5°C and 1.9 W/m2 in
2100 as targets.
How you define 1.5°C will matter, e.g., inwhat year, with what likelihood, withwhich climate model?

Energy CO2 Emissions

DISCUSSION