Allowable carbon emissions lowered by multiple climate targets

Thomas Stocker Climate and Environmental Physics Physics Institute, University of Bern Switzerland

7th Annual Meeting IAMC Meeting, University of Maryland

Collaborators:

Fortunat Joos, Patrik Pfister, Marco Steinacher

Allowable carbon emissions lowered by multiple climate targets

7th Annual Meeting IAMC Meeting, University of Maryland

1.  Cumulative carbon emissions and the 2°C target

2.  Combining climate system targets

3.  Mitigation delay sensitivity

Limiting climate change will require substantial and sustained reductions of

greenhouse gas emissions.

Limiting climate change would require substantial and sustained reductions of

greenhouse gas emissions, which

together with adaptation, can limit climate change risks.

IPC

C 2

013,

Fig

. SP

M.1

0

790 GtC

2°C

Allowable carbon emissions lowered by multiple climate targets

7th Annual Meeting IAMC Meeting, University of Maryland

1.  Cumulative carbon emissions and the 2°C target

2.  Combining climate system targets

3.  Mitigation delay sensitivity

(Steinacher et al., 2013)

UNFCCC Article 2 requires more than one climate target

(Ste

inac

her e

t al.,

201

3)

•  Bayesian approach of model

calibration

•  definition of climate targets

of comparable stringency

•  probabilistic determination

of climate system reponse

chance < 5% that ΔT < 3oC

chance > 95% that ΔT < 3oC

chance = 66% that ΔT < 3oC

CO2 Concentration by 2100 (ppm)

(Ste

inac

her e

t al.,

201

3)

Climate target: Surface air temperature

chance = 66% that OA < 90%

CO2 Concentration by 2100 (ppm)

(Ste

inac

her e

t al.,

201

3)

Climate target: Ocean acidification (loss of saturated waters)

Temperature target (3oC)

Most stringent single target

Multiple targets

(Steinacher et al., 2013)

From single to multiple climate targets

(Steinacher et al., 2013)

Allowable emission budget for multiple climate targets

Allowable carbon emissions lowered by multiple climate targets

7th Annual Meeting IAMC Meeting, University of Maryland

1.  Cumulative carbon emissions and the 2°C target

2.  Combining climate system targets

3.  Mitigation delay sensitivity

2040

2020

2030

Academic scenarios to reach the 2°C target

Clim

ate

Targ

et (°

C)

Starting Year of Emissions Reduction

The closing door of climate targets

(Sto

cker

, 201

3)

Unachievable Climate Targets

Clim

ate

Targ

et (°

C)

Starting Year of Emissions Reduction

(Sto

cker

, 201

3, A

llen

& S

tock

er, 2

014)

Mitigation delay: Peak temperature rises fast

Warming during delay

Delay in mitigation

Mitigation delay sensitivity ΔT/ Δt

Mitigation delay sensitivity in the Bern3D model

(Pfis

ter a

nd S

tock

er, 2

014,

in p

rep.

)

Mitigation delay sensitivity in the Bern3D model

(Pfis

ter a

nd S

tock

er, 2

014,

in p

rep.

)

Mitigation delay sensitivity in the Bern3D model

(Pfis

ter a

nd S

tock

er, 2

014,

in p

rep.

)

Mitigation delay: Peak temperature rises fast

20th century warming: ≈ 0.08 °C per decade

1998 to 2012 warming: ≈ 0.05 °C per decade

Mitigation Delay Sensitivity

≈ 0.4 °C per decade

Committed peak warming rises 3 to 8 times faster than observed warming

1951 to 2012 warming: ≈ 0.12 °C per decade

Conclusions:

7th Annual Meeting IAMC Meeting, University of Maryland

v  2°C target remains a powerful target because many (but not all) climate changes scale with ΔT.

v  However, the 2°C target does not capture all Reasons For Concern: e.g., ocean acidification, sea level rise, ...

v  Multiple targets require even deeper emission cuts.

v  Mitigation Delay Sensitivity (MDS) is a new policy-relevant metric: MDS(T) rises as fast as CO2 emissions.