Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

Global tropospheric ozone distributions, budgets, and radiative forcings from an ensemble of 26 state-of-the-art atmospheric chemistry models have been intercompared and synthesized as part of a wider study into both the air quality and climate roles of ozone. Results from three 2030 emissions scenarios, broadly representing optimistic, likely, and pessimistic options, are compared to a base year 2000 simulation. This base case realistically represents the current global distribution of tropospheric ozone. A further set of simulations considers the influence of climate change over the same time period by forcing the central emissions scenario with a surface warming of around 0.7K. The use of a large multimodel ensemble allows us to identify key areas of uncertainty and improves the robustness of the results. Ensemble mean changes in tropospheric ozone burden between 2000 and 2030 for the 3 scenarios range from a 5% decrease, through a 6% increase, to a 15% increase. The intermodel uncertainty (±1 standard deviation) associated with these values is about ±25%. Model outliers have no significant influence on the ensemble mean results. Combining ozone and methane changes, the three scenarios produce radiative forcings of -50, 180, and 300 mW m-2, compared to a CO 2 forcing over the same time period of 800-1100 mW m-2. These values indicate the importance of air pollution emissions in short- to medium-term climate forcing and the potential for stringent/lax control measures to improve/worsen future climate forcing. The model sensitivity of ozone to imposed climate change varies between models but modulates zonal mean mixing ratios by ±5 ppbv via a variety of feedback mechanisms, in particular those involving water vapor and stratosphere-troposphere exchange. This level of climate change also reduces the methane lifetime by around 4%. The ensemble mean year 2000 tropospheric ozone budget indicates chemical production, chemical destruction, dry deposition and stratospheric input fluxes of 5100, 4650, 1000 and 550 Tg(O 3 ) yr-1, respectively. These values are significantly different to the mean budget documented by the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR). The mean ozone burden (340 Tg(O 3 )) is 10% larger than the IPCC TAR estimate, while the mean ozone lifetime (22 days) is 10% shorter. Results from individual models show a correlation between ozone burden and lifetime, and each model's ozone burden and lifetime respond in similar ways across the emissions scenarios. The response to climate change is much less consistent. Models show more variability in the tropics compared to midlatitudes. Some of the most uncertain areas of the models include treatments of deep tropical convection, including lightning NO x production; isoprene emissions from vegetation and isoprene's degradation chemistry; stratosphere-troposphere exchange; biomass burning; and water vapor concentrations. Copyright 2006 by the American Geophysical Union.

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Multimodel ensemble simulations of present-day and near-future tropospheric ozone

Aviation and global climate change in the 21st century.

Our current understanding of mechanisms that are, or may be, acting to cause climate change over the past century is briefly reviewed, with an emphasis on those due to human activity. The paper discusses the general level of confidence in these estimates and areas of remaining uncertainty. The effects of increases in the so-called well-mixed greenhouse gases, and in particular carbon dioxide, appear to be the dominant mechanism. However, there are considerable uncertainties in our estimates of many other forcing mechanisms; those associated with the so-called indirect aerosol forcing (whereby changes in aerosols can impact on cloud properties) may be the most serious, as its climatic effect may be of a similar size as, but opposite sign to, that due to carbon dioxide. The possible role of volcanic eruptions as a natural climate change mechanism is also highlighted.

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Radiative Forcing of Climate Change

https://elib.dlr.de/59672/1/scientdir.pdf

Transport impacts on atmosphere and climate: Aviation

Three-dimensional (latitude, longitude, altitude) global inventories of civil and military aircraft fuel burned and emissions have been developed for the United States National Aeronautics and Space Administration (NASA) for the years 1976, 1984, and 1992, and by the European Abatement of Nuisances Caused by Air Transport (ANCAT)/European Commission (EC) Working Group and the Deutsches Zentrum fur Luftund Raumfahrt (DLR) for 1991/92. For 1992, the results of the inventory calculations are in good agreement, with total fuel used by aviation calculated to be 129.3 Tg (DLR), 131.2 Tg (ANCAT), and 139.4 Tg (NASA). Total emissions of NOx (as N02) in 1992 were calculated to range from 1.7 Tg (NASA) to 1.8 Tg (ANCAT and DLR). Forecasts of air travel demand and technology developed by NASA and ANCAT for 2015 have been used to create three-dimensional (3-D) data sets of fuel burn and NOx emissions for purposes of modeling the nearterm effects of aircraft. The NASA 2015 forecast results in a global fuel burn of 309 Tg, with a NOx emission of 4.1 Tg (as N02); the global emission index, EI(NOx) (g NOx/kg fuel), is 13.4. In contrast, the ANCAT 2015 forecast results in lower values-a global fuel burn of 287 Tg, an emission of 3.5 Tg of NOx and a global emission index of 12.3. The differences arise from the distribution of air travel demand and technology assumptions. Comments Reprinted from Aviation and the Global Atmosphere, Intergovernmental Panel on Climate Change, J.E. Penner, D.H. Lister, D.J. Griggs, et al. (eds) (Cambridge: Cambridge University Press, 1999), pages 290-331. NOTE: At the time of publication, the author Anu Vedantham was affiliated with the U.S. Department of Commerce. Currently, she is a staff member of the UPenn Libraries at the University of Pennsylvania. Author(s) S. L. Baughcum, J. J. Begin, F. Franco, D. L. Greene, D. S. Lee, M.-L. McLaren, A. K. Mortlock, P. J. Newton, A. Schmitt, D. J. Sutkus, Anu Vedantham, and D. J. Wuebbles This government publication is available at ScholarlyCommons: http://repository.upenn.edu/library_papers/59

/pdf/aircraft-emissions-current-inventories-and-future-scenarios-2nr40oyef7.pdf

Aircraft Emissions: Current Inventories and Future Scenarios

This paper describes the current status of knowledge regarding the impact of aviation on the atmosphere. The growth of the aviation industry is likely to continue in the future and at present there are significant concerns that this will adversely affect climate and local air quality in the vicinity of airports. Indeed, it is possible that air quality may become a constraint to increased capacity of some large hub airports. Currently the radiative forcing impact from aircraft emissions, other than CO2, are not accounted for in the International Civil Aviation Organization emission trading scheme proposals. Taking only this approach, emissions trading could, in theory, increase the radiative forcing, rather than decrease it. The study of improved ‘environmentally friendly’ flight is still in its infancy, however any proposed and actual new developments, in terms of technology and operational practice, should include an environmental assessment.

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The impacts of aviation on the atmosphere

Chapter 5 Transportation and its infrastructure

TheAEROCHEMstudiesofglobalaviationimpactsontheatmosphereutilized3DinventoriesofaviationfuelandNO x forpresent-dayconditions,2015and2050.Theconstructionofthesedatasetsisdescribedandthemainfeaturesofthedatadiscussed.For1991/92and2015thedifferencesbetweentheavailabledatasetsaresmallandcanbeusedwithequalcon”dence.Theweaknessesofthesedatasetsarediscussedanditisshownthatanewinventoryforpresent-dayconditionsisrequiredbecauseoftherapidgrowthoftheaviationsectoroverthepasttenyearsandtheneedtoperformmoresophisticatedimpactassessmentstudies.Apreliminaryanalysisofrealtraf”cmovementsandemissionsandthosederivedfromidealizedinventoriesshowsigni”cantdifferences.Suchdifferencesmayaffectclimateimpactassessmentsofaircraftemissions. Zusammenfassung IndenAEROCHEMUntersuchungenzurAuswirkungderglobalenLuftfahrtaufdieAtmosphare¨ wurdendreidimensionaleDatensatz¨evonFlugzeugtreibstoffundNO x f¨urgegenw¨artigeBedingungenverwendet.DieZusammenstellungdieserDatens¨atzeunddieHauptcharakteristikadieserDatenwerdenhierbeschrieben.Fur¨dieJahre1991/92und2015sinddieUnterschiedezwischendenzurVerfugun¨ gstehendenDatens¨atzengeringundbeidekonne¨ nohneBedenkenverwendetwerden.DieSchwachpunktederDatensatze¨ werdendiskutiertundeswirddemonstriert,dassaufgrunddesschnellenWachstumsdesFlugbetriebsinnerhalbderletzten10JahreeinneuerDatensatzfur¨gegenw¨artig eBedingungenerforderlichist.AuserdemwirddieNotwendigkeitdifferenziertererStudienzurBestimmungderAuswirkungengezeigt.Einevorlau¨”geAnalysezeigt,dassunterUmst¨ande nmitgrosenUnterschiedenzwischentatsachliche¨ mFlugverkehrundEmissionenunddiesbezugliche¨ nDatengerechnetwerdenmuss,dievonidealisiertenDatens¨atze nabgeleitetwurden.DerartigeUnterschiedehabenallerWahrscheinlichkeitnacheinenbedeutendenEin‘ussaufdieBemessungderAuswirkungenvonLuftfahrtabgasenaufdasKlima.

Peter J. Newton

Papers

Aviation and global climate change in the 21st century.

Aircraft Emissions: Current Inventories and Future Scenarios

The impacts of aviation on the atmosphere

Chapter 5 Transportation and its infrastructure

Aviation emissions: present-day and future