FAA CENTER OF EXCELLENCE FOR ALTERNATIVE JET FUELS & ENVIRONMENT

Project manager: Daniel Jacob, FAALead investigator: Steven Barrett, Massachusetts Institute of Technology

Improving Climate Policy Analysis Tools Project 21

Opinions, findings, conclusions and recommendations expressed in this material are those of the author(s)and do not necessarily reflect the views of ASCENT sponsor organizations.

April 18-19, 2017Alexandria, VA

2

Motivation • Aviation is estimated to cause

- 2% of the global anthropogenic CO2 emissions

- 5% of the global anthropogenic radiative forcing

• Impact is expected to increase

• Line-shaped ice clouds, forming behind aircraft jet engines

• Trap more longwave radiation than reflecting shortwave radiation

• Potentially largest single source of aviation-related RF

5% Projected Growth

Agreement for Carbon Neutral Growth from 2020

AdaptedfromICAO

Climate impacts from Contrails:

12

33

37.5

50

0 50 100 150

ChenandGettelman(2016)for2006

Leeetal.(2009)for2005

BurkhardtandKärcher(2011)for2002

IPCC(2013)for2011

Radiativeforcing(mW/m2)

Aviation-related CO2 RF from Lee et al. 2009

+

3

Objectives

Long-term Objectives• Model aviation impacts at finer

spatial and temporal scaleswhile retaining the capability to analyze policy scenarios to inform decision-making

• Develop methodologies to include climate feedbacks and interactions among emissions species

• Alternative fuel projections and modeling capability

• Physics-based contrail impacts implementation

Near-term Objectives• Continue to develop a

reduced-order climate model for policy analysis, consistent with current scientific understanding

• Improve our understanding of contrails and their climate impacts

1

2

4

Current Work and Status

APMT-Impact Climate1 Contrail Analyses2

§ Develop and validate APMT-Impacts Climate Version 24

§ Analyze sensitivities of contrail formation

§ CERM validation against satellite observations

§ Facilitate knowledge transfer P

§ Update derived ratios for rapid estimation of impacts from short-lived forcers

(P)

§ Support current policy analyses (e.g., PM standard)

(P)

§ Support the improvement of global contrail model (CERM)

P1a

1b

2a

5

Recent Accomplishments: APMT-I Climate, Version 24 Updates (1/2)

1a

Objectives of the Updates

§ Bring APMT-Impacts Climate more in line with scientific understanding

§ Create closer alignment between the Interagency Working Group, Social Cost of Carbon and APMT-Impacts Climate

Capture the non-lineareffects associated with CO2sequestrationC

O2

Mod

elin

g

Figure from: Joos et al. (2013)

Impulse Response Functions Under different RCP Scenarios

Goal Method

APMT-IC currently uses a linear impulse response function to model CO2 and does not capture non-lineareffects

6

Goal

Bring climate sensitivity distribution in line with the Interagency Working Group SCC

Method

Update the APMT-IC Climate Sensitivity from a Triangular Distribution to the Roe and Baker (2007) Distribution

Nitr

ate

Coo

ling

Path

way More

comprehensively capture climate impacts of NOx

Clim

ate

Sens

itivi

ty

Recent Accomplishments: APMT-I Climate, Version 24 Updates (2/2)

1a

Update APMT-IC to include the Nitrate cooling pathway published in Brasseur et al. (2016)

7

Recent Accomplishments: Derived Ratios

1b

Impact Metrics used

§ Global Warming Potential (GWP)§ Temperature Potential (TP)§ Integrated Temperature Potential (iTP)§ Net Present Value (NPV)

Motivation & Methodology

§ To add the impact of non-CO2 aviation climate forcers to the published Social Cost of Carbon, Derived Ratios are computed

§ APMT-Impacts Climate is run for one unit of fuel burn § The ratio of the impact of the non-CO2 climate forcer to the CO2

impact is computed

DerivedRatio = Impact1234567829:;9Impact<=>?@>23567

8

Recent Accomplishments:Global Contrail Modeling (1/3)

• Highest resolution of existing contrail models for continental U.S.• Being expanded to run global contrail simulations• Tradeoffs exist across resolution, computational cost, and fidelity

- Ambient temperature and relative humidity can vary over short spatial and temporal scales

- However, computational resources and data availability constraint model resolution.

!

! ! !!

99!

persistent! condensation! trails! evaporate! after! one! hour! in! the! atmosphere.! The! persistent! contrail!

percentage! decreases! at! a! nearly! exponential! rate! for! increasing! lifetime;! a! small! percentage! of!

condensation!trails!(below!1%)!persists!more!than!8!hours!in!the!atmosphere.!

!

Figure% 4.4.% (Left)% Yearly_averaged% radiative% forcing% from% contrail% and% contrail% cirrus% as% computed% by% CERM.%(Right)% Yearly_averaged% RF% from% Burkhardt% and% Kärcher% (2011),% who% use% a% contrail% cirrus% module% (CCMod)%embedded%into%the%climate%model%ECHAM4.%The%right%figure%is%a%subset%of%the%result%obtained%by%Burkhardt%and%Kärcher%(2011),%considering%only%the%U.S.%section%of%the%global%computational%domain%used%in%that%study.%Results%from% CERM% consider% flight% data% from% the% year% 2006% at% a% 13.5% km×13.5% km% resolution,% while% results% from%Burkhardt% and% Kärcher% (2011)% adopt% 2002% flight% data% at% a% 2.8°×2.8°% resolution.% Local% net% RF% values% below% 1%mW/m2%are%not%displayed%in%either%contour.%

Figure!4.4!shows!on!the!left!the!yearlyGaveraged!net!radiative!forcing!from!contrails!and!contrail!cirrus!

from!a!oneGyear!simulation!with!CERM!over!the!United!States,!using!flight!data!from!2006.!On!the!right,!

the! yearlyGaveraged! net! RF! from! contrails! and! contrail! cirrus! as! computed! by! Burkhardt! and! Kärcher!

(2011)! is! showed.! This! result!was! obtained! through! a! global! simulation! of! contrail! and! contrail! cirrus!

cover! using! a! contrail! cirrus! module! (CCMod)! integrated! into! the! global! climate! model! ECHAM4!

(Roeckner!et!al.,!1996).!There!are!significant!differences!between!CERM!and!the!combination!of!models!

used! by! Burkhardt! and! Kärcher! (2011).! First,! the! input! flight! data! refer! to! different! years! in! the! two!

studies,! with! CERM! and! CCMod! using! aviation! data! from! 2006! and! 2002! respectively.! Second,! the!

domain! of! computation! is! different,! with! CERM! focused! on! the! United! States! and! CCMod! applied!

globally.!Third,!the!two!models!have!completely!different!microphysical!schemes,!with!CERM!providing!a!

more! detailed! representation! of! crystal! processes! throughout! contrail! lifetime.! Fourth,! the! spatial!

resolution!used!by!CERM!is!13.5!km!×!13.5!km,!while!ECHAM4!uses!a!resolution!of!approximately!2.8°!×�2.8°!(equivalent!to!a!linear!resolution!of!approximately!250!km!×�320!km!at!typical!U.S.!latitudes).!The!

vertical!resolution!is!similar!for!the!two!approaches,!with!a!separation!between!vertical!levels!of!about!

ARTICLES

NATURE CLIMATE CHANGE DOI: 10.1038/NCLIMATE1068

Latit

ude

Longitude

3 10 30 1001Radiative forcing (mW m¬2)

300

0.010 0.030 0.050 0.070 0.090

a

b

90° W 0 90° E180° 180°

45° N

0

45° S

90° N

90° S

Latit

ude

Longitude

90° W 0 90° E180° 180°

45° N

0

45° S

90° N

90° S

Optical depth0.005 0.110

Figure 3 | Contrail-cirrus radiative forcing and optical depth at 250 hPafor the year 2002. Net radiative forcing (without correcting for long-wavescattering) (a) and solar optical depth (b) of contrail cirrus.

than 300mWm�2 over the eastern US and central Europe. Overmost of the US, Europe, over the North Atlantic flight corridorand also over parts of southeast Asia, net radiative forcing exceeds100mWm�2. Over much of the northern mid-latitudes contrail-cirrus radiative forcing exceeds 30mWm�2. Maxima in radiativeforcing are found in areas of maxima in contrail-cirrus coverage,but radiative forcing is enhanced in areas with large contrail-cirrusoptical depth (Fig. 3b). This means that for a fixed contrail-cirruscoverage, radiative forcing is larger over southeast Asia than in thenorthern mid-latitudes and slightly larger over the eastern US thanover central Europe or theNorth Atlantic flight corridor.

Globally the long-wave radiative forcing due to young contrailsamounts to 5.5mWm�2. This estimate is in line with an earlierestimate of line-shaped-contrail long-wave radiative forcing usingthe samemodel but an independent technique22. The latter estimateis slightly lower because the randomly overlapped visible line-shaped-contrail coverage in the earlier study (0.06%) is slightlysmaller than our visible young-contrail coverage using the sameoverlap assumption (0.07%). Short-wave radiative forcing due toyoung contrails amounts globally to �1.2mWm�2. This valueis about 50% larger than the value we obtain when neglectingthe diurnal cycle of air traffic, resulting from the fact thatmost flights are daytime flights31,32. Net radiative forcing due toyoung contrails amounts globally to 4.3mWm�2, which is atthe lower bound of the range of radiative-forcing estimates forline-shaped contrails3,31. This may imply that our contrail-cirrusradiative forcing constitutes a low estimate as well. Differencesbetween our short-wave and long-wave forcing estimates andthose in the literature are likely to be due to differences in:(1) the spatial and temporal distribution of contrail coverageand its optical depth resulting from the differences in theparameterization schemes; (2) the background cloud fields and

a

b

Latit

ude

90° W 0 90° ELongitude

180° 180°

¬2.0 ¬1.5 ¬1.0 ¬0.5Change in coverage (%)

0.5 1.0 1.5 2.0

60° N

30° N

90° N

0

Latit

ude

90° W 0 90° ELongitude

180° 180°

60° N

30° N

90° N

0

Figure 4 | Change in natural-cirrus coverage due to the presence ofcontrail cirrus. Change in natural-cirrus coverage at the main flight level of230 hPa (a) and when overlapping all ice clouds within one verticalcolumn (b). Dotted lines indicate the 90% confidence interval and solidlines the 95% confidence interval.

their overlap with the contrails; (3) the flight inventories and theirreference years used.

The global net radiative forcing of contrail cirrus is roughly ninetimes that of young contrails, making it the single largest radiative-forcing component connected with aviation. It is important to notethat contrail cirrus have a much shorter lifetime than long-livedgreenhouse gases. This difference in lifetime influences the relativeimportance of contrail cirrus and other forcing agents for climatechangewhen estimating their impact for remote time horizons33.

The uncertainty in the spreading rate effective in ECHAM4–CCMod (ref. 25) introduces an uncertainty in the estimate ofcontrail-cirrus net radiative forcing of ±5mWm�2. The sensitivityof contrail-cirrus radiative forcing to optical depth and ice-particleshape of contrail cirrus, to the flight inventory and to the model’sradiation code is likely to be similar to that of line-shaped contrails.Therefore, we estimate that the uncertainty related to the first twovariables amounts in ECHAM4 to an uncertainty in contrail-cirrusradiative forcing of⇠25% (ref. 34) and⇠15% (ref. 35), respectively.The sensitivity of global radiative forcing to the flight inventory isprobably small35. Furthermore, it has been shown that the radiativeresponse due to contrails varies by ±22% around a multi-modelmean36. An estimate of the combined uncertainty of radiativeforcing would need to take into account the interdependencebetween the different uncertainties.

Reduction of natural cirrus coverage and optical depthContrail cirrus change the water budget of the surroundingatmosphere and therefore can have an impact on natural clouds.Water vapour that is deposited on ice particles within contrail cirrusis not available for formation and deposition in natural cirrus anylonger. Therefore, contrail cirrus have the potential to modulatethe optical properties of natural clouds, delaying their onset andreplacing them, which may partly offset the direct climate impact

56 NATURE CLIMATE CHANGE | VOL 1 | APRIL 2011 | www.nature.com/natureclimatechange

ARTICLES

NATURE CLIMATE CHANGE DOI: 10.1038/NCLIMATE1068La

titud

e

Longitude

3 10 30 1001Radiative forcing (mW m¬2)

300

0.010 0.030 0.050 0.070 0.090

a

b

90° W 0 90° E180° 180°

45° N

0

45° S

90° N

90° S

Latit

ude

Longitude

90° W 0 90° E180° 180°

45° N

0

45° S

90° N

90° S

Optical depth0.005 0.110

Figure 3 | Contrail-cirrus radiative forcing and optical depth at 250 hPafor the year 2002. Net radiative forcing (without correcting for long-wavescattering) (a) and solar optical depth (b) of contrail cirrus.

than 300mWm�2 over the eastern US and central Europe. Overmost of the US, Europe, over the North Atlantic flight corridorand also over parts of southeast Asia, net radiative forcing exceeds100mWm�2. Over much of the northern mid-latitudes contrail-cirrus radiative forcing exceeds 30mWm�2. Maxima in radiativeforcing are found in areas of maxima in contrail-cirrus coverage,but radiative forcing is enhanced in areas with large contrail-cirrusoptical depth (Fig. 3b). This means that for a fixed contrail-cirruscoverage, radiative forcing is larger over southeast Asia than in thenorthern mid-latitudes and slightly larger over the eastern US thanover central Europe or theNorth Atlantic flight corridor.

Globally the long-wave radiative forcing due to young contrailsamounts to 5.5mWm�2. This estimate is in line with an earlierestimate of line-shaped-contrail long-wave radiative forcing usingthe samemodel but an independent technique22. The latter estimateis slightly lower because the randomly overlapped visible line-shaped-contrail coverage in the earlier study (0.06%) is slightlysmaller than our visible young-contrail coverage using the sameoverlap assumption (0.07%). Short-wave radiative forcing due toyoung contrails amounts globally to �1.2mWm�2. This valueis about 50% larger than the value we obtain when neglectingthe diurnal cycle of air traffic, resulting from the fact thatmost flights are daytime flights31,32. Net radiative forcing due toyoung contrails amounts globally to 4.3mWm�2, which is atthe lower bound of the range of radiative-forcing estimates forline-shaped contrails3,31. This may imply that our contrail-cirrusradiative forcing constitutes a low estimate as well. Differencesbetween our short-wave and long-wave forcing estimates andthose in the literature are likely to be due to differences in:(1) the spatial and temporal distribution of contrail coverageand its optical depth resulting from the differences in theparameterization schemes; (2) the background cloud fields and

a

b

Latit

ude

90° W 0 90° ELongitude

180° 180°

¬2.0 ¬1.5 ¬1.0 ¬0.5Change in coverage (%)

0.5 1.0 1.5 2.0

60° N

30° N

90° N

0

Latit

ude

90° W 0 90° ELongitude

180° 180°

60° N

30° N

90° N

0

Figure 4 | Change in natural-cirrus coverage due to the presence ofcontrail cirrus. Change in natural-cirrus coverage at the main flight level of230 hPa (a) and when overlapping all ice clouds within one verticalcolumn (b). Dotted lines indicate the 90% confidence interval and solidlines the 95% confidence interval.

their overlap with the contrails; (3) the flight inventories and theirreference years used.

The global net radiative forcing of contrail cirrus is roughly ninetimes that of young contrails, making it the single largest radiative-forcing component connected with aviation. It is important to notethat contrail cirrus have a much shorter lifetime than long-livedgreenhouse gases. This difference in lifetime influences the relativeimportance of contrail cirrus and other forcing agents for climatechangewhen estimating their impact for remote time horizons33.

The uncertainty in the spreading rate effective in ECHAM4–CCMod (ref. 25) introduces an uncertainty in the estimate ofcontrail-cirrus net radiative forcing of ±5mWm�2. The sensitivityof contrail-cirrus radiative forcing to optical depth and ice-particleshape of contrail cirrus, to the flight inventory and to the model’sradiation code is likely to be similar to that of line-shaped contrails.Therefore, we estimate that the uncertainty related to the first twovariables amounts in ECHAM4 to an uncertainty in contrail-cirrusradiative forcing of⇠25% (ref. 34) and⇠15% (ref. 35), respectively.The sensitivity of global radiative forcing to the flight inventory isprobably small35. Furthermore, it has been shown that the radiativeresponse due to contrails varies by ±22% around a multi-modelmean36. An estimate of the combined uncertainty of radiativeforcing would need to take into account the interdependencebetween the different uncertainties.

Reduction of natural cirrus coverage and optical depthContrail cirrus change the water budget of the surroundingatmosphere and therefore can have an impact on natural clouds.Water vapour that is deposited on ice particles within contrail cirrusis not available for formation and deposition in natural cirrus anylonger. Therefore, contrail cirrus have the potential to modulatethe optical properties of natural clouds, delaying their onset andreplacing them, which may partly offset the direct climate impact

56 NATURE CLIMATE CHANGE | VOL 1 | APRIL 2011 | www.nature.com/natureclimatechange

1 3 10 30 100 300

Yearly'averaged+RF+from+contrails+and+contrail+cirrus

CERM+for+2006 Burkhardt+and+Kärcher+(2011)+for+2002

RadiaEve+Forcing+[mW/m2]

MIT Contrail Evolution and Radiation Model (CERM)

9

Devised relationships for subgrid variations of meteorological data

Recent Accomplishments:Global Contrail Modeling (2/3)

Benchmarki.e. data at fine grid

Data reproduced at coarse gridi.e. averaged at coarse grid resolution

Vertical sum of ice supersaturated regions on 01/01/2013

These statistical relationships enhance contrail simulationsat coarse scale (shown on next slide)

10

Recent Accomplishments:Global Contrail Modeling (3/3)

Benchmarki.e. data at fine grid

Statistical methods applied at coarse gridi.e. use of probability density functions (PDF)

Con

trai

l Len

gth

[m]

Time [hr]

Comparison between contrail simulations at fine grid, coarse grid, and coarse grid with PDF

Vertical sum of ice supersaturated regions on 01/01/2013

Devised relationships for subgrid variations of meteorological data

11

Outcomes and Applications

Expected Outcomes

APM

T-I C

limat

eC

ontr

ails

Mod

el

• Harmonized, state-of-the-science reduced-order tool to model aviation’s climate impacts

• Model interactions and feedbacks between (CO2 and non-CO2) emission species, radiative forcing, and temperature change to inform policy

• Alternative fuel and well-to-tank modeling of climate impacts

• Improved understanding and modeling of contrail formation and persistence as well as the resulting climate impacts

• Understand sensitivities of contrail formation and persistence with respect to future aviation growth as well as aircraft and engine technology

Tools used for domestic and international policy analyses (e.g. CAEP/10 & 11)

• Improve scientific understanding

• Inform future development of reduced-order tool

Applications

12

Interfaces and Communications

Within ASCENT

Code Training and knowledge transfer to§ ASCENT 48 project to

conduct societal CBA of nvPM standard

§ ASCENT 39 project to conduct societal CBA for Naphthalene removal

§ UIUC to conduct code validation

External

§ ICAO/CAEP for discussing climate impacts of CO2standard (Spring 2016)

§ Presentation to OMB (Winter 2015/16)

§ Discussions with MIT Joint Program on the Science and Policy of Global Change (ongoing)

§ NASA Langley for contrail satellite observation program details (ongoing)

+

13

Summary

• Aviation’s impact on climate is significant and heterogeneous in aviation-related emission species (including contrails), space and time.

• Rapid, reduced-order assessment tools are necessary to quantify the costs and benefits of operational changes or policy changes.

• These tools require constant updating to reflect the current state-of the science.

• A framework that accounts for interactions, changes in background concentrations, and spatial nonlinearities may be necessary to capture policy-relevant changes on a regional scale, especially to capture the impacts of contrails.

• Validation of APMT-Impacts Climate v24

• Regional-ization of climate impacts (distribution & regional sensitivities)

• Furthervalidation of contrail modeling

Summary Next Steps

14

References

Contributors• Steven Barrett• Carla Grobler• Lawrence Wong• Raymond Speth• Florian Allroggen• Philip Wolfe

Brasseur, G.P., et al. 2016. Impact of Aviation on Climate: FAA’s Aviation Climate Change Research Initiative (ACCRI) Phase II. Bulletin of the American Meteorological Society 97(4), pp.561-583. Chen, Chih-Chieh, and Andrew Gettelman. "Simulated 2050 aviation radiative forcing from contrails and aerosols." Atmospheric Chemistry and Physics 16.11 (2016), pp. 7317-7333.Joos, F., et al. 2013. Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: a multi-model analysis. Atmospheric Chemistry and Physics 13(5), pp.2793-2825.Lee, David S., et al. "Aviation and global climate change in the 21st century." Atmospheric Environment 43.22 (2009), pp. 3520-3537.Roe, G.H., and Baker, M.B., 2007. Why is climate sensitivity so unpredictable? Science 318(5850), pp.629-632.Stocker, T. F., et al. IPCC, 2013: climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change.