Climate forcing from carbon emissions

Transcription

1 Climate forcing from carbon emissions hilip Goodwin 1 Thanks to: Ric Williams 1, Mick Follows 2, Andy Ridgwell 3, Stephanie Dutkiewicz 2 1 University of Liverpool 2 Massachusetts nstitute of Technology, USA 3 University of ristol

2 Rising atmospheric carbon dioxide ( ): Anthropogenic projection F Aims: A) Relate emissions to steady state ) Consider radiative forcing C) Consider feedbacks gnore carbonate and silicate rock weathering [CC 27] The rise in partial pressure of atmospheric CO 2 ( ) causes a radiative forcing ( F) which alters climate

3 RELATNG EMSSONS TO For the same em, eventually same steady state 25 2 (a) em (Gt C) (b) (ppm) Time (years) Air-sea model response to a em = 2GtC EMSSON: Same steady state

4 RELATNG EMSSONS TO Carbon in the atmosphere and ocean CO 2 (artial pressure, ) ATMOSHERE Atmospheric carbon inventory: A =V atm x OCEAN CO 2 H 2 CO 3 HCO 3 - CO 3 2- Ocean carbon inventory: O =V ocean xc DC C DC = CO 2 + H 2 CO 3 + HCO 3- + CO 3 2- A steady state is reached when: [ ] ocean

5 RELATNG EMSSONS TO Emissions without ocean chemistry Steady state when: CO [ ] 2 Therefore: CO 2 A O Thus proportional to total air-sea carbon: [CO 2 ] And: ( + O A δ δ ( + ) O A ) Special case; O =V ocean x[co 2 ] We can make a ratio: δ = δ Change in air-sea carbon is emission, δ em =δ( A + O ): Therefore we can write: δ ln ( + ) A A A + = δ + em O O O

6 RELATNG EMSSONS TO Emissions with ocean chemistry [CO 2 ] [H 2 CO 3 ] [HCO 3- ] [CO 3 2- ] C DC = CO 2 + H 2 CO 3 + HCO 3- + CO 3 2- At steady state: ut: CO [ ] 2 / + A O We must define a new inventory, [Goodwin et al, 27], that accounts for the dissociation of CO 2 in seawater NO OCEAN CHEMSTRY : OCEAN CHEMSTRY A + O = A + O WHERE: δ = δ C CO 2 DC C DC CO 2 δ ln = δ + A em O δ ln = δ em

7 RELATNG EMSSONS TO GCM experiment: how links to carbon emission SURFACE TEMERATURE ( O C) MT GCM Realistic circulation Realistic carbon cycling Monthly mean forcing Add carbon to atmosphere over ~5years ntegrate for ~3 years for steady state Measure final p (ppm) CURRENT EMSSONS MTGCM CONVENTONAL RESERVES Carbon emission (GtC)

8 RELATNG EMSSONS TO Testing the independent analytical equation Evaluate at pre-industrial steady state for MTGCM integrate by assuming remains constant [Goodwin et al, 27]: ln = em f = i exp em Compare to model results: ANALYTCAL EQUATON NUMERCAL SOLUTON p (ppm) CURRENT EMSSONS MTGCM Our method CONVENTONAL RESERVES Carbon emission (GtC)

9 RELATNG TO F How can CO 2 affect climate? Add CO 2 Radiation imbalance, F Temperature increases, T How do levels affect F (and so T)? F = α ln [Myhre et al, 1998] Why logarithmic? CO 2 only absorbs at certain wavelengths Amount of those wavelengths in atmosphere reduces with increasing An increase in absorbs set fraction of what is left in the atmosphere Therefore, write equations in log form.

10 RELATNG EMSSONS TO F How about Radiative forcing? F (W/m2) GCM Equation Carbon Emissions (GtC) ln [p] F From: We get: = 1.7Wm 2 F F = α em ln ln Using CC [21] α, we find for MTGCM: = = α per 1Gt C em The contribution of today s emissions to the climate from 1 to 5 years cf current forcing ~1.6Wm -2 in transient state ossibly rising to ~7.5Wm -2 lasting for thousands of years

11 CLMATE SENSTVTY Climate sensitivity of the past (1ppm) Evaluate of GENE model forced with palaeo constraints from Ridgwell (25) F for a 1GtC emission (Wm -2 ) Years (Ma) δf α = δ em The present day has a high climate sensitivity

12 CONSDERNG CARON CYCLE FEEDACKS Feedbacks from carbon cycles changes Atmosphere Terrestrial carbon store, Surface ocean Deep ocean iological organic carbon drawdown iological CaCO 3 drawdown Many factors affect in addition to anthropogenic emissions

13 RELATNG OTHER CARON CYCLES TO Testing the independent analytical relations Evaluate at pre-industrial steady state and plot: (a) δ δ (GtC) em ter f Terrestrial = i exp ter (ppm) (b) δc bio +δc dis (global average mol m 3 ) Soft tissue f V C = i exp bio ANALYTCAL EQUATON NUMERCAL SOLUTON 35 3 (c) δc CaCO3 (global average mol m 3 ) f CaCO3 = i O( A C) O( A C) V C CaCO3 exp ( ) A O( A C ) C CaCO3

14 CONSDERNG CARON CYCLE FEEDACKS Time (yrs) Feedbacks from carbon cycles changes over time for: i) 2GtC emission, ii) Change in soft tissue biology, iii) Change in biological CaCO 3 production (ppm)

15 CONSDERNG CARON CYCLE FEEDACKS Time (yrs) Feedbacks from carbon cycles changes Feedbacks combine in a non-linear way to alter ( ) ( ) + ( ) + ( ) overall EMSSON SOFT TSSUE CaCO (ppm)

16 CONSDERNG CARON CYCLE FEEDACKS Time (yrs) Feedbacks from carbon cycles changes Maths predicts: overall = EMSSON SOFT TSSUE CaCO (ppm)

17 Conclusions Analytical link to numerical models: insight into non-linear feedbacks overall = EMSSON SOFT TSSUE CaCO3 Can compare future steady state forcing to present transient levels: resent climate sensitivity to carbon perturbations is large: 1.7Wm -2 per 1Gt C for thousands of years F (W/m2) Carbon Emissions (GtC) GCM Equation ln [p]

18 Why should we assume remains constant? can be expressed in terms of a carbon buffer factor, : y writing: δ[ ] C = [ CO ] δc 2 = A + O DC DC p (ppm) EMSSONS (GtC) p While increases as increases; they have opposing effects on the value of. Causing: << b (GtC) b VALD UNTL ~ 5GtC EMSSONS (GtC)