Ciais p 20150708_1500_upmc_jussieu_-_room_201

Earth system modeling as part of integrated assessment

Thomas Gasser

on behalf of Philippe Ciais

LSCE/IPSL, France

Earth System Models (ESMs)

• ESMs are used by WG1 to project changes in the climate system.

• ESMs can be forced in emission (like in C4MIP). In that case, concentrations of GHG and climate change are calculated.

• ESM can be forced in concentration or radiative forcing (like in CMIP5). In that case, compatible emissions are calculated.

AR5 WG1 Ch 12

• IAMs are used by WG3 to provide projections of emissions based on scenario storylines.

• For mitigation scenarios, climate targets are achieved through exogenous drivers (e.g. conserve forest area) and/or endogenous one (e.g. solve for a carbon price).

• Assumptions are made about technologies in different sectors, their cost and/or rate of implementation, etc.

Integrated Assessment Models (IAMs)

AR5 WG3 Ch 6

IAMs capabilities

• IAMs do not resolve complex biophysical climate feedbacks (e.g. how land management influences regional climate).

• IAMs lack a sophisticated representation of the coupling between biogeochemical cycles and climate (e.g. permafrost, forest dye-back).

• IAMs lack a detailed representation of climate variability (e.g. extreme events, decadal climate variability) and its impact on biogenic emissions and food security.

ESMs capabilities

• ESMs only calculate net compatible emissions consistent with a given climate target, give no information about where and how emission reductions should take place.

• ESM have a too simple description of land management (their effect on C stocks, non-CO2 gases emissions).

• ESM are computer intensive and cannot run a wide range of scenarios, with contrasted emissions from all the different forcers.

Difficulty in WG interaction: the example of negative emissions

• In ESMs, only net negative emissions can be calculated, given a climate target.

• Net negative emissions are obtained by a majority of ESMs by the end of the 21st Century for CO2eq targets between 430 ppm and 580 ppm.

• IAMs implement gross negative emissions (mainly BECCS) earlier in the 21st Century, given their economical and technological assumptions.

• Gross negative emissions from IAMs are significantly larger than net negative emissions from ESMs.

• Both approaches are not comparable, causing a source of confusion.

Negative emissions from WG3 models (IAMs)

Note net negative emissions for CO2eq comprised between 430 ppm and 580 ppm by 2100 Gross negative emissions are not represented separately.

Fuss et al. 2014

Negative emissions from WG1 models (ESMs) for RCP2.6

20002020

20402060

20802100

− 5

0

5

10

15

Eco

mp

(GtC

/yr)

histor ical EFF

MAGICC

default

21502200

22502300

OSCAR

mean

90% range

JUMP-LCM

mean

90% range

ESMs

mean

models

The uncertainty only comes from different representations of climate change, the carbon cycle and their coupling.

Gasser et al. (in press)

The way forward: better offline coupling

EFF

LUC

ECH4

EN2O

[CH4]

[N2O]

[CO2] RF

T°

[OH]

EVOC

ECO

ENOx

[O3]t

EHalo [Halo] [O3]s

CLAND

COCEAN

EOC

ENH3

ESO2

EBC RFant

NLAND

NOCEAN

AER

Energy

An example of the cause-effect chain in an ESM: CO2 is far from being the only driver!

The way forward: better offline coupling

An example of the cause-effect chain in an ESM: CO2 is far from being the only driver!

AR5 WG1 Ch 8

• Ideally, one could build coupled IAM-ESM where

– IAM provides land use drivers and emissions to ESM.

– ESM provides consistent climate change to IAM which feeds back on anthropogenic activities.

– Examples of critical feedbacks:

• Regional climate change due to land use decisions;

• Climate extremes on agricultural yield;

• Climate change effects on biomass production for BECCS and other sectors;

• River discharge for irrigation, power plants cooling, hydro power, other usage of water;

• Climate change effects on future solar and wind power.

The way forward: better online coupling

In the near term: the issue of negative emissions

• BECCS requires detailed projections of biomass production.

• Incorporate BECCS specific crops in ESMs would allow to : – Calculate the needs in resources more accurately

(water, nutrients, climate limitations);

– Calculate soil C change and their effect on atmospheric CO2 and climate;

– Calculate N2O emissions (fertilizers) and their effect on climate.