OVERSHOOT PATHWAYS TO CO2 CONCENTRATION STABILIZATION [Formerly THE - - PowerPoint PPT Presentation

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OVERSHOOT PATHWAYS TO CO2 CONCENTRATION STABILIZATION [Formerly THE - - PowerPoint PPT Presentation

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OVERSHOOT PATHWAYS TO CO2 CONCENTRATION STABILIZATION [Formerly THE EFFECT OF CARBON-CYCLE CLIMATE FEEDBACKS ON THE EMISSIONS REQUIREMENTS FOR CO 2 STABILIZATION] Tom Wigley, National Center for Atmospheric Research, Boulder, CO 80307,

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SLIDE 1

OVERSHOOT PATHWAYS TO CO2 CONCENTRATION STABILIZATION

[Formerly ‘THE EFFECT OF CARBON-CYCLE CLIMATE FEEDBACKS ON THE EMISSIONS REQUIREMENTS FOR CO2 STABILIZATION’]

Tom Wigley, National Center for Atmospheric Research, Boulder, CO 80307, USA wigley@ucar.edu

Presented at: Workshop on GHG Stabilization Scenarios Tsukuba, Japan

  • Jan. 23, 2004
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SLIDE 2

SUMMARY

  • Description of revised carbon cycle model
  • Production of new stabilization profiles accounting for

climate feedbacks

  • Emissions requirements to follow new profiles
  • Quantification of the effect of climate feedbacks on

these requirements

  • Alternative pathways to concentration stabilization
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SLIDE 3

BACKGROUND:

(1) The first CO2 stabilization profiles that attempted to account realistically for economic constraints were the WRE profiles (Wigley,

Richels and Edmonds, Nature 379, 240–243, 1996).

(2) These profiles assumed that concentrations could, initially, only depart slowly from a baseline, no-climate-policy scenario. (3) They also assumed that the date for the beginning of a significant departure was later for higher stabilization targets. (4) Emissions requirements were determined using an inverse carbon cycle model. (5) The original carbon cycle was calibrated to reflect the state of the science in 1995/6, and did not account for climate-related feedbacks on the carbon cycle.

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SLIDE 4

ORIGINAL (WRE) STABILIZATION PROFILES

350 400 450 500 550 600 650 700 750 800 1990 2010 2030 2050 2070 2090 2110 2130 2150 2170 2190 2210 2230 2250 YEAR CO2 CONCENTRATION (ppm) WRE450 WRE550 WRE650 WRE750 BASELINE CONST EFOSS(2000)

Departure points Stabilization points

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SLIDE 5

REVISED CARBON-CYCLE MODEL

QUESTION: How does the revised MAGICC carbon cycle model compare with the other two models used in the IPCC TAR?

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SLIDE 6

Table 1: Comparison of climate feedbacks: 2100 concentrations (ppm) for the IS92a emissions scenario. MODEL

No climate feedbacks With climate feedbacks Increase due to climate feedbacks

Bern

651 706 55

ISAM

682 723 41

MAGICC

675 715 40

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SLIDE 7

CONSTRUCTING NEW STABILIZATION PROFILES

Changes are required because …..

  • there are new baseline no-policy scenarios,
  • there are improved carbon cycle models, and
  • these models now account for climate feedbacks on the

carbon cycle.

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SLIDE 8

SUMMARY OF NEW CONCENTRATION PROFILES

300 350 400 450 500 550 600 650 700 750 800

2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR CO2 CONCENTRATION (ppm) P50 BASELINE 750 650 550 450 350

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SLIDE 9

REVISED EMISSIONS REQUIREMENTS FOR STABILIZATION

  • 2

2 4 6 8 10 12 14 16 18

2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR FOSSIL CO2 EMISSIONS (GtC/yr) P50 BASELINE 750 650 550 450 350

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SLIDE 10

QUANTIFYING THE CLIMATE FEEDBACK INFLUENCE

Climate feedbacks lead to higher concentrations for any given emissions scenario ….. hence ….. For a given concentration profile, climate feedbacks lead to lower emissions requirements

P50 SCENARIO: WITH (FB) AND WITHOUT (NFB) CLIMATE FEEDBACKS

350 400 450 500 550 600 650 700 750 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 YEAR ENDYEAR CO2 CONCENTRATION (ppm

FB NFB

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SLIDE 11

EFFECT OF CLIMATE FEEDBACKS ON EMISSIONS (WRE450)

2 4 6 8 10 12 14 16 18

2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR FOSS IL C O2 E MISS ION S (GtC /yr)

P50 BASELINE NFB FB

OLD WRE

450 ppm

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SLIDE 12

EFFECT OF CLIMATE FEEDBACKS ON EMISSIONS (WRE550)

2 4 6 8 10 12 14 16 18

2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR FOS S IL C O2 E MIS S ION S (GtC /yr)

P50 BASELINE NFB FB (2 cases)

OLD WRE

550 ppm

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SLIDE 13

SUMMARY OF FEEDBACK EFFECT

NFB EMISSIONS minus FB EMISSIONS FOR DIFFERENT STABILIZATION TARGETS 0.5 1 1.5 2 2.5 3 3.5 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR F O SSIL EM ISSIO N S D IF F ER EN C E (G tC /y r) 750 650 550 450 350

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SLIDE 14

EFFECT OF CLIMATE FEEDBACKS ON CUMULATIVE CO2 EMISSIONS

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SLIDE 15

EFFECT OF CLIMATE FEEDBACKS ON CUMULATIVE EMISSIONS (550ppm) 200 400 600 800 1000 1200 1400 1600 1800 2000 2000 2050 2100 2150 2200 2250 2300 YEAR CUMULATIVE FOSSIL CO2 EMISSIONS (GtC) FB NFB

OLD WRE550

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SLIDE 16

RATIO NFB/FB CUMULATIVE EMISSIONS : DIFFERENT STABILIZATION TARGETS

0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR F O S S IL E M IS S IO N S R A T IO (N F B /F B )

750 650 550 450 350

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SLIDE 17

ALTERNATIVE PATHWAYS TO STABILIZATION : OVERSHOOT POSSIBILITIES

  • Except for the 350 ppm stabilization case, all WRE

profiles assume monotonic increases in concentration.

  • What if we allow the profile to go above the stabilization

level and then decline?

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SLIDE 18

550 AND 650 ppm STABILIZATION PLUS 550 ppm OVERSHOOT CASES

350 400 450 500 550 600 650 700 2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR

E N D Y E A R C O 2 C O N C E N T R A T IO N (p p m WRE650 WRE550 OV1 OV2

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SLIDE 19

550 AND 650 ppm STABILIZATION PLUS 550 ppm OVERSHOOT CASES

1 2 3 4 5 6 7 8 9 10 11 12 2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR

F O SS IL C O 2 E M IS SIO N S (G tC /y r) WRE550 WRE650 OV1 OV2

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SLIDE 20

CUMULATIVE EMISSIONS

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR

CUMULATIVE FOSSIL CO2 EMISSIONS (GtC

WRE550 WRE650 OV1 OV2

Overshoot cases allow more emissions for 100+ years, but have very similar asymptotic cumulative emissions. In general, total allowed emissions depends on the stabilization level, but not on the path to stabilization.

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SLIDE 21

TEMPERATURE AND SEA LEVEL CONSEQUENCES OF OVERSHOOT PROFILES

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SLIDE 22

550 AND 650 ppm STABILIZATION PLUS 550 ppm OVERSHOOT CASES

0.5 1 1.5 2 2.5 3 3.5 2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR

G L O B A L -M E A N T E M P E R A T U R E C H A N G E (d e g C WRE550 WRE650

OV1 OV2

Maximum additional warming = 0.2 to 0.3 degC

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SLIDE 23

550 AND 650 ppm STABILIZATION PLUS 550 ppm OVERSHOOT CASES

10 20 30 40 50 60 70 80 2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 2220 2240 2260 2280 2300

YEAR

GLOBAL-MEAN SEA LEVEL RISE (cm

WRE550 WRE650

OV1 OV2

Maximum additional sea-level rise = 4 cm.

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SLIDE 24

SUMMARY OF OVERSHOOT RESULTS FOR DIFFERENT STABILIZATION LEVELS

350, 450, 550 & 650 ppm CONCENTRATION PROFILES, FOSSIL CO2 EMISSIONS, CUMULATIVE FOSSIL CO2 EMISSIONS, GLOBAL-MEAN TEMPERATURE & SEA LEVEL RISE (out to 2400)

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SLIDE 25

CONCENTRATION PROJECTIONS FOR STABILIZATION PROFILES 300 350 400 450 500 550 600 650 700 750 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR ENDYEAR CO2 CONCENTRATION (ppm) 650 550 450 350

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SLIDE 26

FOSSIL EMISSIONS FOR STABILIZATION PROFILES

  • 2
  • 1

1 2 3 4 5 6 7 8 9 10 11 12 13 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR FOSSIL CO2 EMISSIONS (GtC/yr) 650 550 450 350

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SLIDE 27

CUMULATIVE FOSSIL EMISSIONS FOR STABILIZATION PROFILES 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR CUMULATIVE FOSSIL CO2 EMISSIONS (GtC 650 550 450 350

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SLIDE 28

RATE OF CHANGE OF EMISSIONS FOR STABILIZATION PROFILES

  • 2.2
  • 2
  • 1.8
  • 1.6
  • 1.4
  • 1.2
  • 1
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200 YEAR RATE OF CHANGE OF EMISSIONS (GtC/decade 650 550 450 350

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SLIDE 29

TEMPERATURE PROJECTIONS FOR STABILIZATION PROFILES 0.5 1 1.5 2 2.5 3 3.5 4 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR GLOBAL-MEAN TEMPERATURE CHANGE (degC 650 550 450 350

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SLIDE 30

RATE OF CHANGE OF TEMPERATURE FOR STABILIZATION PROFILES 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 YEAR RATE OF TEMPERATURE CHANGE (degC/decade) 650 550 450 350

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SLIDE 31

SEA LEVEL PROJECTIONS FOR STABILIZATION PROFILES 10 20 30 40 50 60 70 80 90 2000 2050 2100 2150 2200 2250 2300 2350 2400 YEAR GLOBAL-MEAN SEA LEVEL RISE (cm 650 550 450 350

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SLIDE 32

CONCLUSIONS

  • For a given emissions scenario, climate feedbacks lead to concentration

increases 10-20% larger than without feedbacks (even larger with some models!)

  • Climate feedbacks lead to substantially lower emissions requirements to

meet any given stabilization target

  • The percentage reduction in cumulative emissions is larger for lower

stabilization targets

  • Overshoot pathways …..
  • delay the time when emissions must begin to decrease by about 10 years
  • can be constructed to both delay and not increase (dE/dt)max
  • allow much larger near-term (100+ years) cumulative emissions
  • lead to small increases in the magnitude of future climate and

sea-level change, and small increases in the rates of change

  • It seems likely that overshoot pathways would reduce mitigation costs much

more than they would increase climate-change damages – unless there are nonlinearities that lead to much larger damages if thresholds are passed

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SLIDE 33

ADDITIONAL MATERIAL ON CHOOSING A STBILIZATION TARGET

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SLIDE 34

WHAT SHOULD THE STABILIZATION TARGET BE? (What does ‘dangerous interference’ mean?)

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SLIDE 35

INPUT PDF FOR GLOBAL WARMING LIMIT (from 2000)

0.1 0.2 0.3 0.4 0.5 0.6 1 2 3 4 5 6 GLOBAL WARMING LIMIT (degC) PROBABILITY DENSITY (degC**-1)

INPUT PDFs : CO2 STABILIZATION CONCENTRATION IS CONTROLLED BY WARMING LIMIT, CLIMATE SENSITIVITY AND NON-CO2 FORCING

INPUT PDF FOR CLIMATE SENSITIVITY

0.1 0.2 0.3 0.4 0.5 1 2 3 4 5 6 CLIMATE SENSITIVITY, ∆T2x (degC) PROBABILITY DENSITY (degC**-1)

INPUT PDF FOR NON-CO2 FORCING

1 2 3 4 NON-CO2 FORCING (W/m**2) 0.1 0.2 0.3 0.4 0.5 0.6 0.7

  • 1

PROBABILITY DENSITY (m**2/W)

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SLIDE 36

CO2 CONCENTRATION STABILIZATION TARGET

0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 0.0018 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 CO2 CONCENTRATION (ppm) PROBABILITY DENSITY (ppm**-1)

HIGH SENSITIVITY HIGH NON-CO2 FORCING LOW SENSITIVITY LOW NON-CO2 FORCING Median (615ppm)

10%

LOW WARMING LIMIT HIGH WARMING LIMIT

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SLIDE 37

C O N C L U S IO N

  • T h e C O 2 s ta b iliz a tio n ta rg e t d e p e n d s o n w h a t is

ju d g e d to b e ‘d a n g e ro u s in te rfe re n c e ’, th e c lim a te s e n s itiv ity , a n d fo rc in g fro m n o n -C O 2 s o u rc e s .

  • T h e re is a p ro b a b ility o f a ro u n d 1 0 % th a t th e

ta rg e t c o u ld b e b e lo w th e c u rre n t le v e l.