glen peters center for international climate and environmental research – oslo (cicero)
TRANSCRIPT
Glen PetersCenter for International Climate and
Environmental Research – Oslo (CICERO)
SBSTA Meeting (Bonn), 3-4 April, 2012
Why iGTP (integrated GTP)?
Another metric just complicates matters?
SBSTA Meeting (Bonn), 3-4 April, 2012
A primer…
Integrated response to a pulse emission equals
instantaneous response to a sustained emission
Mathematical property of a convolution for a linear R
SBSTA Meeting (Bonn), 3-4 April, 2012
SBSTA Meeting (Bonn), 3-4 April, 2012
SBSTA Meeting (Bonn), 3-4 April, 2012
SBSTA Meeting (Bonn), 3-4 April, 2012
Why iGTP (integrated GTP)?
• In the early days of the GWP, research focussed on iGTP!
• At some stage, the link from radiative forcing to temperature was lost.
• Is the iGTP similar to the GWP?
SBSTA Meeting (Bonn), 3-4 April, 2012
iGTP=GWP?BC
SF6N2O
CH4
Within about 5-10% for a range of TH (except for BC)
But why?
SBSTA Meeting (Bonn), 3-4 April, 2012
Why? Two cases
• Absolute metrics• AGWP, AGTP, iAGTP
• Relative metrics• GWP, GTP, iGTP• Reference gas important!
• Different reasons for similarities
SBSTA Meeting (Bonn), 3-4 April, 2012
Use Box-Diffusion Energy-Balance Model (EBM)
• Metrics use Impulse Response Functions• IRFs 1-1 mapping with box-diffusion EBM
• Analytical solutions
• Easy problem (?)• Don’t need a GCM to understand the
physics…
SBSTA Meeting (Bonn), 3-4 April, 2012
Example, 3 layer box modelF T/λ
c1
c3
c2
k1
k2
Mixed-layer
Intermediate
Deep
SBSTA Meeting (Bonn), 3-4 April, 2012
1 layer box model
F T/λ
SBSTA Meeting (Bonn), 3-4 April, 2012
1 layer box model
F
T/λ
Energy going in
Energy going out
Change in energy
SBSTA Meeting (Bonn), 3-4 April, 2012
1 layer box model
F
T/λ
Instantaneous RF
Instantaneous T
Rate of change T
For a pulse emission…
SBSTA Meeting (Bonn), 3-4 April, 2012
1 layer box model
AGWP
iAGTP/λ
AGWP
~iAGTP
~AGTP
Integrate for a pulse emission…
One equation linking the AGWP, AGTP, iAGTP
SBSTA Meeting (Bonn), 3-4 April, 2012
EBM Interpretation
• AGWP: Cumulative energy added to the system (integrated forcing)
• iAGTP/λ: Cumulative energy lost from the system (feedbacks, back to space)
• OHC/AGTP: Energy currently in the system• OHC: in the ocean• AGTP: in the surface-mixed layer
SBSTA Meeting (Bonn), 3-4 April, 2012
Absolute metrics
BC
SF6
N2O
CH4
1. A pulse emission decays to zero, 2. thus the energy in the system decays to zero3. and for energy balance the accumulated
energy in equals the energy out
iAGTP AGWP
“Inertia” dictates the difference
SBSTA Meeting (Bonn), 3-4 April, 2012
Normalized metrics
• If iAGTP AGWP, then it does not imply iGTP GWP
• Why? The reference gas…
• The idea of a reference gas is to represent the other gases
SBSTA Meeting (Bonn), 3-4 April, 2012
iGTP=GWP?BC
SF6N2O
CH4
Within about 10% for a range of TH (except for BC)
But why?
SBSTA Meeting (Bonn), 3-4 April, 2012
A thought experiment…
• Suppose X is the reference gas• X has a lifetime as for CH4 and twice RF
• What is GWP, GTP, iGTP?• GWP=GTP=iGTP=0.5
• N2O is the “universal” gas
• GWP~GTP~iGTP
SBSTA Meeting (Bonn), 3-4 April, 2012
Does GWP=iGTP?
• Depends on the reference gas…
• Does CO2 represent the other species well?
SBSTA Meeting (Bonn), 3-4 April, 2012
CO2 response can capture time scales of CH4, N2O, and SF6
CO2 response can’t capture time scale of BC
SBSTA Meeting (Bonn), 3-4 April, 2012
CO2 as a reference
BC
SF6N2O
CH4
CO2 does a bad job for BCCO2 does a good job for N2O
Can estimate if CO2 over/under estimates
Why is GWP≠GTP? The path is different…
SBSTA Meeting (Bonn), 3-4 April, 2012
CO2 as a reference for CH4
RF
iAGTPAGTP
AGWP
SBSTA Meeting (Bonn), 3-4 April, 2012
Does GWP=iGTP?
• Depends on the reference gas AND metric…
• CO2 as a reference
• GWP~iGTP: GWP and iGTP are integrations• Except for very short lived species
• GWP≠GTP: GTP is a pathway (instantaneous)
SBSTA Meeting (Bonn), 3-4 April, 2012
Does GWP=iGTP=GTP?
• It is often argued• “GWP and GTP are different since they are a
different responses”
• I would argue• “GWP and GTP are different since the
reference gas is bad”
SBSTA Meeting (Bonn), 3-4 April, 2012
Details
• Possible to look into more technical details• Climate model parameterisation• Fluxes in and out of different ocean layers• …
• Read the paper
SBSTA Meeting (Bonn), 3-4 April, 2012
Conclusion
• iAGTP AGWP for a pulse emission since RF,T 0 and energy balance requires the energy in to equal the energy out
• iGTP GWP since the reference gas (CO2) is good enough for integrated metrics
• GWP≠GTP since the reference gas (CO2) is not good enough for the pathway of RF
SBSTA Meeting (Bonn), 3-4 April, 2012
Policy Implications
• If integrated temperature is the goal of climate policy, then GWP is a simple metric with a similar response
• Common metrics are connected• The importance of CO2 as a reference gas is
underappreciated• Reference gas may be more important for
instantaneous metrics (e.g., GTP)
• How does CO2 affect metric values?