Joint Planning & Development Office Environmental Integrated Product Team

Partnership for AiR Transportation Noise and Emissions Reduction

Workshop on the Impacts of Aviation on Change: Add Picture A Report of Findings and Recommendations June 7-9, 2006, Cambridge, MA Executive Summary

August 2006

REPORT N0. PARTNER-COE-2006-004-SUMMARY 1

Contents Report Authors...... 2 Acknowledgement...... 3 Executive Summary...... 4 A. Emissions in the UT/LS and Resulting Chemistry Effects ...... 6 B. Contrails and Cirrus...... 7 C. Climate Impacts and Climate Metrics ...... 10 D. Studies for Trade-offs Amongst Aviation Emissions Impacting Climate ...... 12 Appendices...... 13 Appendix 1 Workshop Agenda ...... 14 Appendix 2 Workshop Participants/Authors for Each Subgroup...... 16 Appendix 3 Other Attendees at the Workshop...... 17

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Report Authors*

Workshop Chair Donald Wuebbles University of Illinois-Urbana Champaign

Subgroup Leaders Anne Douglass NASA GSFC Bernd Kärcher IPA/DLR, Germany Wei-Chyung Wang SUNY Albany

Other Invited Participants Steve Baughcum Boeing Co. Robert P. d'Entremont AER, Inc. Andy Dessler Texas A & M Univ. Paul Ginoux GFDL NOAA Redina Herman Western Illinois Univ. Andy Heymsfield MMM/ESSL NCAR Ivar Isaksen Univ. Oslo, Norway Daniel Jacob Harvard Univ. Sanjiva Lele Stanford Univ. Jennifer Logan Harvard Univ. J. McConnell York Univ., Canada Rick Miake-Lye Aerodyne Res. Inc. Pat Minnis LaRC NASA Dave Mitchell DRI Dan Murphy NOAA CSD/ESRL Laura Pan NCAR Joyce Penner Univ. Michigan Michael Prather Univ. California-Irvine Jose Rodriguez NASA GSFC Karen Rosenlof ESRL NOAA Ken Sassen Univ. Alaska-Fairbanks Robert Sausen IPA/DLR, Germany Keith Shine Univ. Reading, UK Azadeh Tabazadeh Stanford Univ. Ian Waitz MIT Ping Yang Texas A & M University Fangqun Yu SUNY-Albany

*Appendix 2 lists participants by subgroups and Appendix 3 lists other attendees

Acknowledgement I first want to acknowledge the effort of the Next Generation Air Transportation Sys- tem/Joint Planning and Development Office (NGATS/JPDO) Environmental Integrated Product Team (EIPT) and the Partnership for AiR Transportation Noise and Emissions Reduction (PARTNER) in getting the Workshop established and to thank the FAA Office of Environment and Energy and NASA Science Mission Directorate’s Applied Science Program for providing the support for setting up the actual Workshop. Given that there were no special travel funds provided for attending the Workshop, I also thank the many organizations that contributed this to the participants. The Subgroup leaders, Anne Douglass, Bernd Kärcher, and Wei-Chyung Wang, did a wonderful job of chairing their sessions and organizing the writing for the Workshop report. A special thank you to Mohan Gupta and Malcolm Ko for their extensive help with the meeting preparations and in reviewing this report. I also greatly appreciate the additional reviews of the report we received from David Fahey, Mark Jacobson, and Brian Toon. Finally, I want to also express a big thank you to all of the speakers and participants for their time and efforts. The community interest and participation in this Workshop was exemplary, particularly given the short-lead time for the Workshop. It is this community interest and involve- ment in establishing the relevance of the issues and in laying the groundwork for the re- search associated with aviation and that will lead to the successful new research efforts we all hope will result from this Workshop.

Workshop Chair Don Wuebbles

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correctly capture the climate impacts of Executive Summary aviation emissions. The effects of aircraft emissions on the As a first step in response to the need to current and projected climate of our address these issues, the Next Genera- planet may be the most serious long- tion Air Transportation System/Joint term environmental issue facing the Planning and Development Office aviation industry [IPCC, 1999; Aviation (NGATS/JPDO) Environmental Inte- and the Environment – Report to the grated Product Team (EIPT)1 and the United States Congress, 2004]. How- Partnership for AiR Transportation ever, there are large uncertainties in our Noise and Emissions Reduction present understanding of the magnitude (PARTNER)2 convened a panel of ex- of climate impacts due to aviation emis- perts from around the world to partici- sions. With extensive growth in demand pate in a “Workshop on the Impacts of expected in aviation over the next few Aviation on Climate Change” during decades, it is imperative that timely ac- June 7-9, 2006 in Boston, MA. The tion is taken to understand and quantify stated goals of the workshop were to the potential impacts of aviation emis- assess and document the present state sions to help policymakers address cli- of knowledge of climatic impacts of avia- mate and other potential environmental tion; to identify the key underlying uncer- impacts associated with aviation. tainties and gaps in scientific knowl- The climatic impacts of aviation emis- edge; to identify ongoing and further re- sions include the direct climate effects search needed and to make prioritized from carbon dioxide (CO2) and water recommendations as to how additional vapor emissions, the indirect forcing on funding may be leveraged to take ad- climate resulting from changes in the vantage of other on-going funded re- distributions and concentrations of search programs; to explore the devel- ozone and methane as a consequence opment of metrics for aviation climate- of aircraft nitrogen oxide (NOx) emis- related trade-off issues; and to help fo- sions, the direct effects (and indirect ef- cus the scientific community on the avia- fects on clouds) from emitted aerosols tion-climate change research needs. and aerosol precursors, and the climate effects associated with contrails and cir- rus cloud formation. To enable the de- 1 The EIPT is one of eight integrated product velopment of the best strategy to miti- teams of the NGATS/JPDO charged with the gate these climatic impacts scientists role of formulating a strategy that allows aviation must quantify these impacts and reduce growth consistent with the environmental-related goals of NGATS. The JPDO, jointly managed by current uncertainties to enable appropri- FAA and NASA, serves as a focal point for co- ate action. The only way to ensure that ordinating the research related to air transporta- policymakers fully understand trade-offs tion for all of the participating agencies (Federal from actions resulting from implement- Aviation Administration, NASA, the Departments ing engine and fuel technological ad- of Commerce, Defense, Homeland Security, Transportation, and the White House Office of vances, airspace operational manage- Science and Technology Policy). ment practices, and policy actions im- 2 posed by national and international bod- PARTNER is a Center of Excellence supported by the Federal Aviation Administration, the Na- ies is to provide them with metrics that tional Aeronautics and Space Administration, and Transport Canada.

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This report documents the findings and sources of carbon dioxide, the expecta- recommendations of the Workshop. tion is that this percentage will increase While the report does not represent a because of projected increase in avia- peer reviewed assessment, the intention tion and the likely decrease in other is to use the results to provide guidance combustion sources as the world moves for the agencies and private sector away from fossil fuels towards renew- stakeholders participating in the EIPT to able energy sources. In addition, air- develop and implement an aviation cli- craft nitrogen oxides released in the up- mate research plan to reduce uncertain- per troposphere and lower stratosphere ties to “levels that enable appropriate generally have a larger climate impact actions” [Next Generation Air Transpor- than those emitted at the surface, al- tation System-Integrated Plan, 2004]. though some of the much larger surface emissions from energy and transporta- A major internationally coordinated effort tion sources also reach the upper tropo- to assess the impacts of aviation on the sphere. global was sponsored by the U.N.’s Intergovernmental Panel on The workshop participants acknowl- Climate Change (IPCC, 1999). Since edged the need for focused research then, while new information has become efforts in the United States specifically available, there has been no compre- to address the uncertainties and gaps in hensive attempt to update the assess- our understanding of current and pro- ment of the science and the associated jected impacts of aviation on climate uncertainties. During this time period, and to develop metrics to characterize there have also been discussions of these impacts. This could be done how to define the best metrics to ac- through co-ordination and/or expansion count for the wide range of spatial and of existing and planned climate research temporal scales of aviation-induced cli- programs or may entail new activities. mate impacts. This workshop agreed Such efforts should include strong and with IPCC (1999) that the three most continuing interactions between the sci- important ways that aviation affects cli- ence community, aviation system opera- mate are (1) direct emissions of green- tors and policy developers to ensure house gases including CO2 and water that the most up-to-date science is read- vapor, (2) emissions of NOx that interact ily available for policy considerations with ozone, methane, and other green- and that scientists are aware of the house gases, and (3) persistent con- questions and challenges faced by op- trails and their effects on cirrus cloud erators and policy developers. Partici- distribution. For this workshop, our focus pants were asked to provide both short- was on the impacts of subsonic aviation term (three to five years) and long-term emissions at cruise altitudes in the up- prioritized research needs with achiev- per troposphere and lower stratosphere able goals and objectives that can help (UT/LS) and on the potential response to address the uncertainties and gaps of the climate system to these emis- associated with key questions on avia- sions. However, it is also recognized tion induced climate impacts. These re- that all aircraft emissions must be con- search priorities also include the need to sidered. identify, develop and evaluate metrics to characterize the climate impacts of avia- Although current fuel use from aviation tion to aid the policy-making process. is only a few percent of all combustion

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Research into the environmental effects background state, emphasizing the of aircraft emissions cannot be decou- composition of the upper troposphere pled from basic atmospheric research, and the transition from the troposphere such as fundamental understanding of to the lowermost stratosphere. Im- the physics and chemistry in the UT/LS provements to the representation of the region and aerosol-cloud interactions in atmospheric circulation have resulted in the context of global climate modeling. better models for the composition and The overall science focus of this work- fluxes of ozone and other species in this shop was divided into three particular region. The magnitude of this flux and Subgroups: (1) Emissions in the UT/LS its spatial and seasonal variability are and resulting chemistry effects, (2) Ef- similar to quantities derived from obser- fects of water and particle emissions on vations in some models, and uncertain- contrails and on cirrus clouds, and (3) ties have been reduced. These im- Determining the resulting impacts on provements should help to better assess climate from aircraft emissions and de- the aviation impacts. There are continu- fining metrics to measure these impacts. ing efforts that compare simulations with observations that will likely lead to de- velopment of observation-based per- formance metrics for atmospheric mod- Key Findings els.

A. Emissions in the UT/LS and Uncertainties and Gaps Resulting Chemistry Effects One family of uncertainties in evaluating State of the Science aviation effects on climate derives from specific model formulation errors and The potential importance of aircraft can be addressed by laboratory, nu- emissions of nitrogen oxides (NOx) (and merical, or atmospheric studies that fo- also from hydrogen oxides (HOx) from cus on the specific process. water vapor emissions into the strato- • Aircraft emissions of gases and parti- sphere) on tropospheric and strato- cles. Remaining uncertainties in the spheric ozone has been recognized for emissions, both from uncertainties in several decades. The effects on ozone how much is emitted (e.g., soot, sul- (O3) can also affect the production of fates) from each aircraft and from un- tropospheric OH and thus affect levels certainties in the global distribution of of methane (CH4). There have been these emissions with altitude, latitude, substantial improvements in the chemis- and longitude, need further considera- try-transport modeling tools used to tion. evaluate the impacts of aviation NOx The fundamental NOx and HOx chem- emissions on O3 and CH4 since the • 1999 IPCC assessment. The database istry of the upper troposphere. Large of observations in the UT/LS has been disagreements between the modeled greatly expanded, and data from the and measured abundances of HOx European MOZAIC program (instru- and NOx gases in the upper tropo- ments on commercial aircraft) and fo- sphere point to errors in either the cused field campaigns are commonly measurements or in the tropospheric being used to evaluate the global model chemical mechanisms and rates. This

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discrepancy is not found in the lower tion or other breakdowns in atmos- stratosphere. pheric stability are a major uncertainty in evaluating aviation impacts today. • Lightning NOx. Better understanding of lightning NOx in terms of sources Research Recommendations and and their relationship to convection is Priorities needed to evaluate the aircraft pertur- bation, especially for future . • Models and Measurements Intercom- parison. A Models and Measurements • Plume processing of aircraft NOx in Intercomparison, emphasizing the the first 24 hours. Better understand- UT/LS and free troposphere, should ing of the possible conversion of NOx be conducted. This process should to nitric acid (HNO3) in the aircraft lead to model improvements and re- plume needs to be attained. duction of uncertainty in model predic- A second type of uncertainty involves tions. coupling across different system • Vertical transport processes between components, and possible non-linear 2 and 10 km. Additional measure- responses to perturbations and/or feed- ments and data analyses, along with backs within the chemical system. modeling analyses, are needed to re- • The coupling and feedbacks of tropo- duce uncertainties in treatment of con- spheric CH4-CO-OH-O3. There is no vection and other transport processes, single test (based on observations) and in the treatment of lightning ef- that gives confidence that any model fects. accurately responds to a NOx pertur- • Data analysis and modeling. Expand bation. the analysis of the wealth of data be- • Climate change. Analyses of future ing obtained in the UT/LS by different aircraft fleets need to be considered aircraft and satellite platforms to fur- relative to the climate expected. Most ther constrain the magnitude and sea- model studies and all observations of sonality of turnover rates and mixing the and background processes. chemistry are derived from today's • Re-examine the impacts of aviation in climate. the UT/LS using several of the im- • Scavenging. The process whereby proved models. gaseous HNO3 (and thus NOx) is re- In the longer-term, field campaigns may moved from the atmosphere involves be needed to address issues with HOx- large-scale transport, convection, NOx chemistry in the UT and to better cloud processes and precipitation. understand background processes. Fur- This coupling is a major uncertainty in ther improvements are needed in labo- current chemistry-transport models. ratory studies of heterogeneous proc- • Transport and Mixing. Aircraft emis- esses and low-temperature kinetics. sions will accumulate in atmospheric regions of relatively slow, or stagnant mixing. The seasonality of these re- B. Contrails and Cirrus gions, the apparent barriers to mixing, and the rapid mixing through convec- State of the Science

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Contrails form if ambient air along the to modify high cloudiness in the ab- flight track is colder and moister than a sence of contrails is affected by the fre- threshold based on known thermody- quent observation of high supersatura- namic parameters. Contrails initially tions with respect to the ice phase, the contain more but smaller ice crystals relatively small number of heterogene- than most cirrus clouds. Early contrail ous ice nuclei (IN) in cirrus conditions, evolution depends, in not well under- and the ever-presence of mesoscale stood ways, on aircraft and engine temperature fluctuations inducing large emission parameters. At times contrails cooling rates and setting the stage for organize themselves in long-lived, re- cirrus formation. gional-scale clusters in ice supersatu- rated air masses. The radiative effect of Uncertainties and Gaps contrails is different during the day than A number of uncertainties and gaps at night. Aircraft-induced contrail-cirrus were identified in contrail-cirrus and add significantly to the natural high other aircraft-induced effects on cirrus cloud cover and have the potential, al- clouds: beit with large uncertainties, for a rela- Plume particle processing. It is not well tively large positive (di- • understood how properties (number rect effect). Line-shaped contrails are concentration, surface area, composi- only a portion of the total climate impact tion, and mixing state) of ambient of aviation on the cloudiness. aerosols are perturbed in the presence Recent correlation analyses between of jet engine emissions under various real-time regional-scale air traffic atmospheric conditions and aircraft movements and the occurrence of con- configurations. Detailed investigations trail structures detectable with satellites, of the microphysical and chemical suggest the global coverage of persis- processes governing the evolution of tent, spreading contrails (contrail-cirrus) aviation aerosols in the time scale of and inferred radiative forcing might be days after emission is required. underestimated by an order of magni- Optical properties of contrails, contrail- tude or more, but large uncertainties • cirrus, and cirrus. Factors controlling remain. the radiative properties of cirrus clouds Homogeneous freezing of supercooled and contrail-cirrus (ice crystal habit, aqueous solution droplets initiated by vertical profiles of ice water content, rapid mesoscale temperature fluctua- effective radius) are poorly constrained tions is a ubiquitous pathway to form cir- by observations. The balance between rus clouds in-situ globally. A global im- cooling from reflection of sunlight and pact of aircraft soot particles processed warming from trapping of heat radia- in dispersing plumes on cirrus (indirect tion is also poorly understood. effect) cannot be excluded. By number, Detection and prediction of ice super- aviation might double the background • saturation. Contrails and the expan- black carbon loading in the UT/LS. The sion of contrails into cirrus clouds oc- indirect effect depends, along with de- cur in an ice supersaturated environ- tails of plume processing, on the ability ment. However, the global distribution of background aerosol particles to act as of supersaturation in the upper tropo- ice-forming nuclei. The potential of soot sphere is not adequately known. particles emitted by aircraft jet engines

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• In-situ measurements of aerosol a single class of clouds in terms of chemistry and small ice crystals. Cir- their radiative properties; thus they are rus ice crystals can range from a few not capable of predicting contrail-cirrus to hundreds of !m or more in size. cloud fraction from first principles. Measuring this large range requires • Representation of aerosols and con- several instruments and improved trails in global atmospheric models. agreement between instruments. Ex- Both models and satellite datasets isting instrumentation also cannot eas- lack the horizontal and vertical resolu- ily measure the shape of the numer- tion to address many contrail issues. ous very small crystals that have been Data useful for validation of aerosol found in contrails and cirrus clouds. modules is lacking, especially for car- • Properties of heterogeneous ice nuclei bonaceous aerosol. Global models from natural and anthropogenic and contrail/cirrus studies need to es- sources. The atmospheric effects of tablish the essential parameters for ice formation from aviation particles properly incorporating aviation aero- depend on the ice nucleation proper- sols and their effects into atmospheric ties of particles from other anthropo- calculations. genic and natural sources. However, • Long-term trends in contrail-cirrus and concentration and chemical composi- cirrus. Long-term trends can only be tion of IN in the upper troposphere are ascertained from consistent measure- not well known and are difficult to pre- ments over extensive periods, but the dict with models. current satellite record has many un- • Interactions between heterogeneous certainties, limiting the ability to exam- ice nuclei and cirrus clouds. Ice nu- ine past trends. Special care is needed cleation processes occur within short to ensure homogeneous datasets for time scales and are rather localized. estimation of future trends in cirrus Hence it is difficult to determine their measurements. relative importance using in-situ measurements. Ice nucleation path- Research Recommendation and Pri- ways can be isolated in the laboratory, orities but the question arises whether the • In-situ probing and remote sensing of employed IN particles are representa- aging contrail-cirrus and aircraft tive. This issue is particularly important plumes. A series of coordinated re- for aircraft because real engine soot gional-scale campaigns should be de- and its processing cannot easily be signed and executed to measure the represented in laboratory measure- appropriate variables using in-situ and ments. remote sensing measurements with • Incorporation of effects of aviation- the aim to characterize the growth, de- induced particles and cirrus into global cay and trajectories of contrail ice par- models. Accurate knowledge of ice ticle populations. Such measurements supersaturation is crucial for quantify- are also needed to define the abun- ing direct and indirect effects of avia- dance and properties of ambient aero- tion on cirrus cloudiness. Most current sols as well as gaseous aerosol pre- models do not adequately represent cursor concentrations in the tropo- ice supersaturation, and treat cirrus as sphere.

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• Regional studies of supersaturation approaches and methods of IN meas- and contrails using weather forecast urements. models have the potential to include Long-term research needs include: (1) our best physics and the high resolu- development or improvement of instru- tion needed to more accurately predict ments that help establish background supersaturation. Development of these concentrations and characteristics of models and associated observational heterogeneous ice nuclei and measure datasets may be the best approach for supersaturation accurately, and (2) the developing our knowledge in the near development and implementation of new term, supporting development of more concepts for ice phase-related micro- accurate tools for use in global mod- physics, supersaturation, radiation, and els. cloud fraction in climate models ena- • Global model studies addressing direct bling a consistent treatment of global and indirect effects. Enhance the aviation effects. treatment of relevant processes, in- The current suite of satellite instruments cluding appropriate parameterizations, is inadequate for evaluating supersatu- in global climate models (GCMs) to ration. Higher resolution (both horizon- improve analyses of contrails and cir- tally and vertically) is required for the rus associated with aircraft. observations. Very accurate measure- • Use of existing or upcoming informa- ments of temperatures as well as water tion from space-borne sensors. Inves- vapour mixing ratio are required to de- tigate the optical and microphysical rive high quality fields of relative humid- properties of contrail and contrail- ity. cirrus, e.g., optical thickness and ef-

fective particle sizes (parameters that are essential to the study of the radia- C. Climate Impacts and Climate tive forcing of these clouds) from Metrics space-borne sensors. • Process studies of plume and contrail State of the Science development. Studies that explore the In assessing the overall impact of avia- role of emitted aerosol particles, and tion on climate, and to quantify the po- how volatile aerosols interact with tential trade-offs on the climate impact each other and with background aero- of changes in aircraft technology or op- sols, are required to understand the erations, metrics for climate change are indirect effect. Studies that investigate needed to place these different climate contrail development as a function of forcings on some kind of common scale. emissions and aircraft design and how Radiative forcing (RF) has been used as contrails evolve into cirrus-like clouds a proxy for climate impact for well-mixed would better quantify the direct effect. greenhouse gases. However, recent • Laboratory measurements of ice nu- analyses have demonstrated that a unit cleation. Laboratory data are urgently radiative forcing from different climate needed to develop aerosol-related pa- change mechanisms does not necessar- rameterisations of heterogeneous ice ily lead to the same global mean tem- nucleation for use in models. It is also perature change (or to the same re- recommended to compare different gional climate impacts). The concept of

11 efficacy (E) has been introduced to ac- exception of the radiative forcing from count for this (i.e., E depends on the the CO2 emissions. The ozone and specific perturbation to the climate sys- methane RFs from NOx emissions are tem, such as changes in ozone or aero- opposite in sign, so the extent to which sol distributions related to aircraft emis- they offset each other is an important sions). Hence, it is the product of E and uncertainty. Estimates for contrails and RF that should be evaluated and inter- cirrus are particularly highly uncertain. compared for the various climate im- • Optical properties of contrails, contrail- pacts from aviation. However, RF is not cirrus, and cirrus. As discussed in pre- an emissions metric capable of compar- vious section. ing the future impact of different aviation emissions. The applicability of emission • Defining metrics for trade-offs. The metrics, such as Global Warming Poten- scientific community may be able to tials (GWPs), have not been adequately define useful metrics for the climate tested and evaluated. In addition, change and climate impacts associ- changes in precipitation and other cli- ated with aviation, but further study mate variables besides temperature are and consensus building is needed. of interest. Climate metrics for aviation need to be done in the context of cli- Recommended Research and Priori- mate metrics for other short-lived per- ties turbations from other sectors. • Radiative effects on climate from con- trails and cirrus. In addition to previ- An update of the IPCC (1999) radiative ously mentioned studies, specific stud- forcing (RF) from aviation for the “cur- ies aimed at better understanding the rent” time period finds that, with one ex- climate impacts from contrails and cir- ception, the IPCC findings have not rus. Intercomparisons (model to significantly changed, apart from the in- model) and evaluations (compare crease in air traffic from 1992 to 2000 model to observations) of climate and (Sausen et al., 2005). The exception is radiative transfer models. RF from linear contrails, which appear to be at least a factor of three smaller. • Systematic model intercomparison of There is still no reliable estimate of RF efficacy studies. Evaluate inhomoge- from aviation-induced cirrus clouds. neous vertically and horizontally dis- Based on recent correlation analyses tributed forcing agents. Analyze cirrus some authors suggest that this RF might changes, ozone changes, CH4, and di- be dominating all other aircraft effects. rect particle effects, and effects of It is critical that appropriate metrics be changes in climate state. established before assuming relative • Identify, develop and evaluate metrics climate impacts for various contributions for climate impact assessment and based on potentially inappropriate met- examine their scientific basis. rics. • Quantify the uncertainty in proposed Uncertainties and Gaps metrics and how it propagates (both • Climate impacts are highly uncertain. parametric input uncertainties and There remain significant uncertainties model uncertainties). on almost all aspects of aircraft envi- ronmental effects on climate, with the

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D. Studies for Trade-offs Amongst of radiative forcing for aviation may not Aviation Emissions Impacting provide an appropriate basis for making Climate policy or operational decisions (time- dependent effects likely necessary), nor Along with furthering scientific under- are they an appropriate basis for fully standing, there are policy-related needs evaluating the relative impacts of vari- for sensitivity analyses of the net effects ous aviation effects. This argument is of trade-offs between various interven- not new; indeed, it is widely understood tions in aircraft operations and emis- and accepted, and a variety of alterna- sions including: tive integral measures have been pur- • NOx reduction technology versus fuel sued. efficiency (i.e., CO emissions) 2 • flight altitude effects (e.g., effects on ozone and contrail formation) There is currently no study in the peer • changing future geographical distribu- reviewed literature that can be cited to tions of the fleet justify, based on the scientific under- • differential impact of day/night opera- standing of the impact of aviation emis- tions sions, the possible choices of metrics • routings to avoid certain regions with suitable for trade-off application. Re- specialized chemistry (e.g. supersatu- search is needed to examine the effect rated air, cirrus, or polar) of different metrics, and the choices • studies of the co-dependence of within each metric (e.g. time horizon), physical impacts, e.g. how future cli- on evaluating the relative importance of mate change may alter the ozone re- different aviation emissions. Such stud- sponse ies would need to explore the potential of existing metrics and the possibility of designing new metrics. It must be Climate change metrics are expected to stressed that even if there is a philoso- play an important role in these analyses. phical agreement on an acceptable met- The IPCC report provided instantaneous ric, current atmospheric models may not forcing due to the cumulative impacts of be able to calculate these metrics with aviation. While this is a measure of how acceptable accuracy. the atmosphere has changed due to his- torical aviation activities, such estimates

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Appendices

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Appendix 1

Workshop Agenda

Workshop on the Impacts of Aviation on Climate Change

June 7-9, 2006 Boston, MA June 7 8:00 - 9:00 a.m. Registration and Breakfast* 9:00 - 9:10 a.m. Mohan Gupta – Welcome and logistics 9:10 - 9:25 a.m. Lourdes Maurice – Motivation and Vision for the Workshop: JPDO/NGATS/FAA Context 9:25 - 9:40 a.m. Malcolm Ko – The EIPT-S/M Panel charge to the workshop 9:40 - 10:15 a.m. Don Wuebbles – Science overview, workshop goals & objectives, expected outcomes and format 10:15 - 10:30 a.m. Break 10:30 - Noon Charge to subgroup leaders: Key questions by the subgroup lead- ers and general discussion Don Wuebbles – Discussion leader 10:30 - 11:00 a.m. Anne Douglass – UT/LS and Chemistry Effects 11:00 - 11:30 a.m. Bernd Kärcher – Contrails and Cirrus Clouds 11:30 - Noon W.-C. Wang – Climate Impacts and Climate Metrics Noon - 1:00 p.m. Lunch 1:00 - 3:00 p.m. Parallel subgroup meetings Focus: Review the present state of scientific knowledge and key underlying uncertainties 3:00 - 3:15 p.m. Break 3:15 - 5:15 p.m. Plenary session: Updates from each subgroup with discussions, (approx. 40 minutes each) Don Wuebbles – Discussion leader 5:15 - 5:30 p.m. Don Wuebbles – Summary and charge for the next session

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June 8 - 8:00 a.m. Breakfast* 8:00 - 10:00 a.m. Parallel subgroup meetings Focus: Explore the metrics of aviation emissions relative to other emissions. Discuss the aviation-related trade-off issues. Identify the gaps in aviation-related research needs. 10:00 - 10:15 a.m. Break 10:15 - 11:45 a.m. Plenary session: Updates from each subgroup with discussions, (approx. 30 minutes each) Don Wuebbles – Discussion leader 11:45 - Noon Don Wuebbles – Summary and charge for the next session Noon - 1:00 p.m. Lunch 1:00 - 3:00 p.m. Parallel subgroup meetings Focus: Identify short- and long-term priorities of aviation needs. Identify the ongoing and already planned future research programs and make recommendations on how to leverage upon them to meet aviation needs. 3.00 - 3.15 p.m. Break 3:15 - 4:45 p.m. Plenary session: Updates from each subgroup with discussions, (approx. 30 minutes each) Don Wuebbles – Discussion leader 4:45 - 5:00 p.m. Don Wuebbles – Summary and charge for the next session

June 9 - 8.00 a.m. Breakfast* 8:00 - 10:00 a.m. Parallel subgroup meetings Focus: Develop final consensus on all issues. 10:00 - 10:15 a.m. Break 10:15 - 12:30 p.m. Plenary session: Updates from each subgroup with discussions, (approx. 45 minutes each) Don Wuebbles – Discussion leader 12:30 - 12:55 p.m. Discussion on publication of the final report, involvement of at- tendees, review and overall schedule. Don Wuebbles – Discussion leader 12:55 - 1:00 p.m. Concluding remarks – Mohan Gupta, Malcolm Ko, Don Wuebbles 1:00 p.m. Adjourn

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Appendix 2

Workshop Participants/Authors for Each Subgroup

Workshop Chair: Don Wuebbles, Univ. Illinois - Urbana Champaign

Subgroup 1: Emissions in the UT/LS and Resulting Chemistry Effects Anne Douglass, GSFC NASA : Subgroup Leader Ivar Isaksen, Univ. Oslo, Norway Daniel Jacob, Harvard Univ. Jennifer Logan, Harvard Univ. J. McConnell, York Univ., Canada Dan Murphy, CSD/ESRL NOAA Laura Pan, NCAR Michael Prather, Univ. California-Irvine Jose Rodriguez, GSFC NASA

Subgroup 2: Contrails and Cirrus B. Kärcher, IPA/DLR, Germany : Subgroup Leader Steve Baughcum, Boeing Co. Robert P. d'Entremont, AER, Inc. Andy Dessler, Texas A & M Univ. Paul Ginoux, GFDL NOAA Andy Heymsfield, MMM/ESSL NCAR Sanjiva Lele, Stanford Univ. Rick Miake-Lye, Aerodyne Res. Inc. Pat Minnis, LaRC NASA Dave Mitchell, DRI Karen Rosenlof, ESRL NOAA Ken Sassen, Univ. Alaska Azadeh Tabazadeh, Stanford Univ. Ping Yang, Texas A & M Univ. Fangqun Yu, SUNY-Albany

Subgroup 3: Climate Impacts and Climate Metrics Wei-Chyung Wang, SUNY-Albany : Subgroup Leader Redina Herman, Western Illinois Univ. Joyce Penner, Univ. Michigan Robert Sausen, IPA/DLR, Germany Keith Shine, Univ. Reading, UK Ian Waitz, MIT Don Wuebbles, Univ. Illinois - Urbana Champaign

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Appendix 3

Other Attendees at the Workshop

Nathan Brown, FAA Mohan Gupta, FAA Curtis Holsclaw, FAA Brian Kim, Volpe Center DOT Malcolm Ko, LaRC NASA Joel Levy, NOAA Karen Marais, MIT Lourdes Maurice, FAA Chris Roof, Volpe Center DOT Saleem Sattar, Transport Canada