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Climatic Change, 117 (4), ISSN:0165-0009, ISSN:1573-1480

Multi-gas approaches to climate change policies require a metric establishing ?equivalences? among emissions of various species. Climate scientists and economists have proposed four classes of such metrics and debated their relative merits. We present a unifying framework that clarifies the relationships among them. We show that the Global Warming Potential, used in international law to compare greenhouse gases, is a special case of the Global Damage Potential, assuming (1) a finite time horizon, (2) a zero discount rate, (3) constant atmospheric concentrations, and (4) impacts that are proportional to radiative forcing. We show that the Global Temperature change Potential is a special case of the Global Cost Potential, assuming (1) no induced technological change, and (2) a short-lived capital stock. We also show that the Global Cost Potential is a special case of the Global Damage Potential, assuming (1) zero damages below a threshold and (2) infinite damage after a threshold. The UN Framework Convention on Climate Change uses the Global Warming Potential, a simplified cost-benefit concept, even though the UNFCCC frames climate policy as a cost-effectiveness problem and should therefore use the Global Cost Potential or its simplification, the Global Temperature Potential.

This report gives an overview of five possible regulation schemes for carbon dioxide emissions from international shipping. The strengths and weaknesses of the schemes are compared with regard to nine criteria. The two main categories are standard-based and market-based regulation. Standard-based regulation may have a higher acceptability than market-based regulation, but at a cost of a weaker incentive effect to reduce emissions than in the case of market-based regulation.

Current climate policies are based on the use of the Global Warming Potential (GWP) index to compare various greenhouse gases. Yet, from an economic point of view, more efficient methods exist. The purpose of this paper is to examine the potential cost savings from applying an efficient and more flexible metric as compared to using GWPs, given some long-term goal for stabilization of the climate. We also calculate the costs when only emissions of carbon dioxide (CO2) are targeted. As compared to the least cost multi-gas flexible case, we estimate that the mitigation costs are increased by about 2% by using GWPs, which amounts to about 16-106 Billion US $ per year depending on the stabilization goal. If only CO2 emissions are targeted, costs increase by about 11%. Given our assumptions we conclude from this that most cost savings that stem from including non-CO2 greenhouse gases in climate policy may be realized when applying GWPs, even though these gas tradeoffs are rather different from the efficient ones.

The Global Warming Potential (GWP) is used within the Kyoto Protocol to the United Nations Framework Convention on Climate Change as a metric for weighting the climatic impact of emissions of different greenhouse gases. The GWP has been subject to many criticisms because of its formulation, but nevertheless it has retained some favour because of the simplicity of its design and application, and its transparency compared to proposed alternatives. Here a new metric, which we call the Global Temperature Change Potential (GTP), is proposed which is based on a simple analytical climate model that represents the temperature change at a given time due to either a pulse emission of a gas or a sustained emission change relative to a similar emission change of carbon dioxide. The GTP for a pulse emission illustrates that the GWP does not represent well the relative temperature response; however, the GWP is shown to be very close to the GTP for a sustained emission change for time horizons of 100 years or more. The new metric retains the advantage of the GWP in terms of transparency, and the relatively small number of input parameters required for calculation. However, it has an enhanced relevance, as it is further down the cause-effect chain of the impacts of greenhouse gases emissions. The GTP for a sustained emission appears to be robust to a number of uncertainties and simplifications in its derivation and may be an attractive alternative to the GWP.

The Kyoto Protocol has an ambitious reporting and review system to assess nations’ compliance with their emission commitments. This system requires considerable resources to assure that the Parties report accurate emission inventory data. In spite of this, there is a danger that Parties consciously or unconsciously report erroneous data. The agreed upon review process will likely only detect large discrepancies. Because a more stringent review system would be more costly, there is a need to establish more precisely the needed accuracy to assess compliance. Emissions can alternatively be monitored by independent “top-down” methods; by measuring concentrations of gases in the atmosphere and employing meteorological models. However, all these means are as yet too imprecise to serve as independent alternatives to the emission inventories reported by the Parties to the Kyoto Protocol. Still, they could be useful to monitor the success of the protocol. The top-down approaches might serve to some extent as useful supplements to the traditional emission inventories, in particular those dealing with fluorinated gases, and thereby provide input for improving the methods and guidelines of the emission inventories.

The paper gives a brief description of natural and man-made forces behind climate change and outlines climate variations in the past together with a brief synopsis likely future impacts of anthropogenic emissions of greenhouse gases. The paper also gives a briefing on the background, organisation and functioning of the Intergovernmental Panel on Climate Change (IPCC).

The preliminary emission scenarios in the Special Report on Emission Scenario (SRES) developed by the Intergovernmental Panel on Climate Change (IPCC), will eventually replace the old IS92 scenarios. By running these scenarios in a simple climate model (SCM) we estimate future temperature increase between 1.7°C and 2.8°C from 1990 to 2100. The global sea level rise over the same period is between 0.33 m and 0.45 m. Compared to the previous IPCC scenarios (IS92) the SRES scenarios generally results in changes in both development over time and level of emissions, concentrations, radiative forcing, and finally temperature change and sea level rise. The most striking difference between the IS92 scenarios and the SRES scenarios is the lower level of SO2 emissions. The range in CO2 emissions is also expected to be narrower in the new scenarios. The SRES scenarios results in a narrower range both for temperature change and sea level rise from 1990 to 2100 compared to the range estimated for the IS92 scenarios. Comparison of the B2 scenario with the IS92a scenario show that the effects of lower SO2 emissions will reduce the cooling and result in higher temperature increase in the short run. Near the end of the century this trend is reversed by the effects of the reductions in CO2 emissions earlier in this century, resulting in less temperature increase in B2 than in the old IS92a scenario in 2100.

Viktige ozonnedbrytende stoffer som KFK-11 og KFK-12 er sterke drivhusgasser med direkte oppvarmingseffekt. Men fordi disse gassene bryter ned ozonlaget, har de også flere indirekte effekter som sannsynligvis virker avkjølende. Det er derfor vanskelig å bestemme netto-effekten av disse gassene. Beregninger tyder imidlertid på at oppvarmingseffekten er dominerende for de fleste av dem.

This paper gives a documentation of a simple climate model for studying the effects of future climate gas emissions on global mean temperature and sea level. Input to the model is global emissions of 29 gases. Atmospheric concentration of carbon dioxide (CO2) is calculated on the basis of work published by Joos et al. (1996). The parameterisation is founded on complex models for the carbon cycle where the exchange of carbon between the atmosphere, the biosphere and the oceans is considered. Future concentrations of other gases are calculated by standard equations based on emissions and chemical decay of the different gases in the atmosphere. Radiative forcing from the modelled concentrations in source gases is calculated by applying standard parameterisations published in the literature. In addition, radiative forcing is calculated for soot and sulphate aerosols (direct and indirect effects) as well as the secondary components tropospheric and stratospheric ozone and stratospheric water vapour. The estimated radiative forcing serves as input to an energy-balance-climate/upwelling-diffusion-ocean model developed by Professor Michael E. Schlesinger (Schlesinger et al., 1992). The global and hemispherical change in annual mean temperature is calculated based on the exchange of energy between the atmosphere and the oceans, and the transport of energy in the ocean. The model uses prescribed values for climate sensitivity based on GCM results. The change in sea level rise is both determined by the melting of glaciers and the thermal expansion of the ocean. The model is similar to those applied by IPCC for scenario studies (IPCC, 1996 p 316-318; IPCC, 1997; Wigley and Raper, 1992). Presently, the model serves as a useful tool in the analysis of possible global climatic changes caused by present and future greenhouse gas emissions. However, the intention is to extend the model so that regional predictions of temperature and other climate variables can be carried out.

I denne publikasjonen har vi søkt å presentere ulike metodar for å samanlikne effekten av utslepp av klimagassar. Det globale oppvarmingspotensialet (GWP) er utvikla av FN sitt klimapanel (IPCC) til dette formålet. Dette konseptet har ein viktig funksjon i politiske avvegingar mellom ulike klimagassar. GWP tener det formål den var sett til, nemleg å samanlikne det akkumulerte strålingspådrivet som pulsutslepp av ulike gassar resulterer i. GWP som eit mål for gassen sin oppvarmingseffekt er derimot meir problematisk. Klimagass utslepp vert vekta etter kva tidshorisont ein vel. Det er heller ikkje vilkårleg kva gass ein vel å redusere m.o.t. temperaturendring. Dette vert ytterlegare forsterka då indeksen er sensitiv overfor ulike scenario m.o.t. framtidig utslepp og atmosfæren si samansetning og kjemi. Ei økonomisk tilnærming søkjer å finne ei løysning på den naturvitskapelege statiske indeksen. Dette innebær at ein diskonterer framtidig skade. Slik vert samanlikning og avveging mellom ulike gassar basert på diskontert oppvarmingspotensial eller diskonterte marginale utsleppskostnader. Ei slik tilnærming kan kvantifisere endra oppvarmingspotensial/ utsleppskostnader. Til no viser det seg at desse alternative metodane ikkje har noko gjennomslagskraft hjå avgjerdstakarar.

Concluding remarks: On the nature of the climate problem The problem of climate change is not, despite popular conception, mainly a problem of increased global average temperature. The seriousness of the problem is more related to the potential variability and instability of the global climate and the local weather. We now know that the climate system in the past has shown great and rapid fluctuations for ‘natural’ causes. The stable climate regime observed after the last ice age is currently perturbed by the large outpouring of greenhouse gases due to human activities of many kinds. The question then is whether the stability of the current climate regime is able to withstand this kind of disturbance. The answer to this we really do not know at present. Furthermore, if the climate system should change to a more unstable regime, it is very difficult to predict the local and even regional consequences with any precision. Thus, the problem of climate change is riddled with uncertainties, and the main challenge for us in this situation is to devise a rational response to this uncertainty. Certainly we should be willing to pay some form of insurance premium in order to reduce the risk of damaging climate change, but how high a premium? And how much of the premium should be in the form of greenhouse gas emission reductions and how much in the form of investments in better defence against a more unstable climate? IPCC’s work is important in allowing us to get a best possible scientific foundation for answering these questions. However, providing an academic answer is one thing, to get a politically feasible answer is another. The merging of the scientific consensus and the political realities is therefore necessary, and the processes in the plenary sessions of IPCC are therefore important steps in the direction of providing practical answers to the challenge of climate change.

Formålet med denne rapporten er å gjennomgå klimaprosessen fra forarbeidet til Klimakonvensjonen fram til forhandlingene om Berlin-mandatet om større forpliktelser for industrilandene til å redusere sine utslipp av klimagasser. Perspektivene trekkes fram til det tredje partsmøtet til Klimakonvensjonen i Kyoto, Japan, i desember 1997, der Berlin-mandat forhandlingene skal sluttføres. I tillegg gis det en statusoversikt for klimaforskningen og mulige menneskeskapte klimaforstyrrelser slik dette er oppsummert i de tre rapportene FNs klimapanel (IPCC) publiserte i 1996. Rapporten er laget på oppdrag fra Norsk Hydro a.s. Drivhuseffekten Det eksisterer en naturlig drivhuseffekt som holder jordens middeltemperatur ca. 34° C høyere enn den ville ha vært uten denne effekten. Den naturlige drivhuseffekten skyldes tilstedeværelse av vanndamp (H2O), skyer, karbondioksid (CO2), metan (CH4), lystgass (N2O) og ozon (O3) i atmosfæren. Økte konsentrasjoner Siden før-industriell tid har konsentrasjonen av CO2 i atmosfæren økt med ca. 30%. I samme periode har konsentrasjonen av metan økt med 145%. Dagens konsentrasjoner av disse gassene ligger langt over variasjonsområdet for de siste 220 000 år. Konsentrasjonen av lystgass ligger ca 15% over før-industrielt nivå. Det er bred enighet om at økningen i konsentrasjonene av disse gassene i all hovedsak skyldes menneskeskapte utslipp. Menneskenes aktiviteter har også tilført atmosfæren drivhusgasser som ikke forekommer naturlig i atmosfæren. Forsterket drivhuseffekt Den menneskeskapte økningen i konsentrasjonene av drivhusgasser har ført til en endret strålingsbalanse for jord/atmosfære-systemet og en forsterket drivhuseffekt. Dette vil etter all sannsynlighet føre til en global oppvarming og et annerledes klima. Økningen i atmosfærens CO2-konsentrasjon betyr mest (ca. 60%) for den menneskeskapte forsterkningen av drivhuseffekten. De menneskeskapte utslippene av CO2 skyldes først og fremst bruk av fossile brensler og avskoging i tropiske strøk. Utslipp av svoveldioksid (SO2) omdannes til partikler som reduserer solinnstrålingen. Dette har dempet noe av oppvarmingseffekten av drivhusgassene, men effekten er begrenset til visse områder. Slike partikler gir også avkjøling gjennom å påvirke skyenes utbredelse og egenskaper, men det er vesentlig usikkerhet knyttet til betydningen av denne effekten. Reduksjon av "ozonlaget" i stratosfæren har også hatt en avkjølingseffekt, mens økt konsentrasjon av ozon i troposfæren (de nederste 15 km av atmosfæren) har gitt en oppvarmingseffekt. En merkbar menneskeskapt klimaeffekt Målinger viser at jordens gjennomsnittlige overflatetemperatur har økt med mellom 0.3 og 0.6° C siden slutten av 1800-tallet. De siste årene har vært blant de varmeste i denne perioden, til tross for avkjølingseffekten av vulkanutbruddet på Filippinene i 1991, som førte til økte konsentrasjoner av partikler i atmosfæren. Oppvarmingen er ikke jevnt fordelt geografisk og sesongmessig, og noen områder er blitt kjøligere de siste tiårene. FNs klimapanel, IPCC, konkluderer med at "hovedtyngden av datamaterialet (…) tyder på en merkbar menneskeskapt påvirkning på det globale klima". Klimapanelet påpeker imidlertid at det er usikkerhet knyttet til sentrale forhold som størrelse og mønster for naturlig langtidsvariasjon. Konklusjonen om en sannsynlig menneskeskapt oppvarming støttes av nyere publiserte studier, men analysene er beheftet med begrensinger og usikkerhet. Framtidige klimaendringer Det er mange faktorer som i dag begrenser forskernes evne til å beregne framtidige klimaendringer. Store og raske klimaforandringer har forekommet tidligere og slike endringer er vanskelige å forutsi. Framtidige klimaendringer kan medføre uforutsette konsekvenser. På grunnlag av scenarier for framtidige utslipp og omfattende studier med klimamodeller har IPCC beregnet en sannsynlig økning i global middeltemperatur på mellom 1 og 3.5° C fra 1990 til år 2100. En oppvarming på 2° C oppgis som beste estimat. Gjennomsnittlig oppvarmingshastighet vil sannsynligvis være større enn hva man har hatt de siste 10 000 år. Havnivået vil stige som følge av havets termiske utvidelse og smelting av isbreer og innlandsis. Modellene beregner en økning i havnivået på 15 til 95 cm fra i dag og fram til år 2100. En stigning på 50 cm oppgis som beste estimat. Framtidige klimaendringer vil sannsynligvis ha følgende trekk: Om vinteren vil oppvarmingen over land bli sterkere enn over hav. Oppvarmingen blir størst på høye nordlige breddegrader om vinteren. Om vinteren vil det bli økt nedbør og jordfuktighet på høye breddegrader. Vannets kretsløpet vil bli akselerert. Dette innebærer endringer i forekomst av tørke og flom. Flere dager med ekstrem varme, og færre dager med ekstrem kulde. Det kan bli flere ekstreme nedbørsperioder i noen områder. Det er svært usikkert hvordan klimaendringer vil arte seg på regional skala, og hvilke effekter dette vil ha på økosystemer og ulike sektorer av samfunnet. Analyser tyder på at konsekvensene blir større for utviklingsland enn for industriland, både fordi økonomiene i utviklingsland i større grad er basert på primærnæringene, som sannsynligvis er de mest utsatte sektorene ved klimaendringer, og fordi disse landenes kapasitet til å håndtere klimaendringer sannsynligvis er mindre enn industrilandenes. Klimakonvensjonen FNs generalforsamling opprettet i 1990 en forhandlingskomité med mandat til å utarbeide forslag til et internasjonalt avtaleverk som et første skritt for å løse klimaproblemet (Intergovernmental Negotiating Committee for the Framework Convention on Climate Change). På toppmøtet i Rio de Janeiro i juni 1992 ble forslaget til konvensjon, United Nations Framework Convention on Climate Change (FCCC), signert av 155 stater. Per desember 1996 hadde 164 land ratifisert Klimakonvensjonen, deriblant Norge. Klimakonvensjonen har som mål å stabilisere konsentrasjonene av klimagasser i atmosfæren på et nivå som forhindrer en farlig menneskeskapt påvirkning av klimasystemet. Klimakonvensjonen er en rammekonvensjon som ikke pålegger landene juridisk bindende forpliktelser til å redusere sine utslipp av klimagasser. Den inneholder en intensjonserklæring om å stabilisere utslippene på 1990-nivå innen år 2000. Landene skal rapportere om utslipp av klimagasser og tiltak som iverksettes for å redusere utslippene. Klimakonvensjonen skiller mellom tre hovedgrupper land: Annex II, Annex I, og ‘andre land’. Annex II land er de industrilandene som var medlem av OECD i 1992. Disse landene har flest forpliktelser. Annex I inkluderer alle Annex II land i tillegg til de landene som er i en overgangsfase til å bli markedsøkonomier. Denne gruppen av land har noen færre forpliktelser enn Annex II gruppen. ‘Andre land’ er stort sett utviklingsland, og har færrest forpliktelser. Berlin-mandatet På det første partsmøtet til Klimakonvensjonen i Berlin våren 1995 ble forpliktelsene til å redusere utslippene av klimagasser i Klimakonvensjonen kjent utilstrekkelige for å nå dens mål. For å styrke forpliktelsene til Annex I landene ble det såkalte ‘Berlin-mandatet’ vedtatt. I følge Berlin-mandatet skulle forhandlinger igangsettes for å vedta en protokoll eller annet juridisk instrument med sikte på å styrke forpliktelsene for Annex I landene for perioden etter år 2000. Forhandlingene skjer i ‘The Ad Hoc Group on the Berlin Mandate’ (AGBM), og skal avsluttes før det tredje partsmøtet til Klimakonvensjonen i desember 1997. Det skal settes kvantifiserte og tidsfestede mål for utslippsreduksjoner for årstall som 2005, 2010 og 2020, samt at det skal bestemmes nødvendige tiltak og virkemidler. Både i Klimakonvensjonen og Berlin-madatet fastslås det at man skal ta hensyn til partenes ulike utgangspunkt, ulike økonomiske strukturer og ressursbaser. Forhandlingene om Berlin-mandatet Det har blitt gjennomført seks forhandlingsmøter i AGBM fram til mars 1997. De store industrilandene og EU har vært sene med å konkretisere sine posisjoner, og flere mindre industriland avventer de større partenes posisjoner. Selv om det er de industrialiserte landene som skal ta på seg nye forpliktelser er utviklingslandene aktive. Øystatene (AOSIS) ønsker en omfattende og ambisiøs protokoll. OPEC-landene og noen andre utviklingsland er bekymret for at tiltak i industrilandene kan få negative konsekvenser for dem. Mange land har kommet med innspill til en protokoll. Under møtet i mars 1997 klarte EU å samle seg om å gå inn for å redusere utslippene med 15% i 2010 sammenlignet med 1990 og en intern byrdefordeling. Under samme møte ble det utarbeidet en forhandlingstekst, der overlappende forslag er fjernet, mens all substans gjenstår til senere forhandlingsmøter. Landenes utgangspunkt og interesser Landenes interesser og posisjoner i forhandlingene bestemmes av faktorer som forventede kostnader ved å redusere utslippene av klimagasser, forventede kostnader for landet knyttet til framtidige klimaendringer, holdningene og posisjonene til andre land, og politiske forhold og kultur/livsstil i landet. Forventede kostnader av tiltak avhenger blant annet av samlet målsetting for utslippsreduksjon i Annex I gruppen av land, byrdefordelingen, og graden av kostnadseffektivitet. Både i forhold til folketall og inntektsnivå varierer utslippene av karbondioksid betydelig mellom industrilandene. Blant OECD-landene har USA, Australia og Canada spesielt store utslipp i forhold til bruttonasjonalprodukt og folketall. Disse forskjellene kan forklares gjennom store variasjoner i økonomisk struktur og bruken av ulike energivarer. Landene i omstilling til markedsøkonomi har relativt store utslipp fordi energieffektiviteten er lav. OECD-landenes posisjon i markedene for fossile brensler er også viktig for deres interesser i klimaforhandlingene. De store nettoeksportørene er Norge (olje og gass), Canada (gass, olje og kull) og Australia (mest kull). Det finnes mange studier der kostnaden ved å redusere utslippet av karbondioksid for et land er beregnet som prosent av bruttonasjonalproduktet. De beregnede kostnadene for et land varierer noe med forutsetningene som er lagt til grunn og modellen som er brukt. Landenes posisjoner i forhandlingene De viktigste temaene i forhandlingene som landene har ulike posisjoner knyttet til er: Skal landene ha like eller differensierte mål? Australia, Island, Japan, Norge og Sveits har levert konkrete forslag til differensiering av forpliktelser, mens mange andre land støtter prinsippet. USA er imot differensiering, mens EU har fått til en intern differensiering men er imot differensiering utad. Frankrike gikk også inn for differensiering før EU samlet seg om en posisjon. En formulering i EUs forslag som åpner for differensiering på lenger sikt kan oppfattes som en konsesjon til Frankrike. Mål for og tidfesting av utslippsreduksjoner. Av de største aktørene er det bare EU som har avslørt sine forslag til tidfestet mål; 15% reduksjon i 2010 i forhold til 1990, i tillegg til et mål for 2005 som vil bli presentert senere. USA og Japan har ennå ikke lagt sine forslag på bordet. Norge mener at 10-15% reduksjon i utslippene i 2010 sammenlignet med 1990 for Annex I landene er realistisk. AOSIS går inn for å redusere utslippene med 20% i 2005. Valg av tiltak og virkemidler. De fleste partene støtter handel med kvoter og felles gjennomføring av klimatiltak. AOSIS, Norge og Sveits nevner koordinerte avgifter. EU går inn for å gruppere tiltakene i tre grupper etter graden av internasjonal koordinering. USA ønsker at det skal være helt opp til hvert land å velge virkemidler. Fleksibilitet i oppfylling av forpliktelser over tid. Den viktigste forkjemperen for mest mulig fleksibilitet i oppfyllingen av forpliktelser over tid er USA, mens mange andre land er mer skeptiske til dette fordi tiltakene kan bli utsatt og kontrollproblemer kan oppstå. Kun karbondioksid eller en ‘kurv’ av klimagasser? De fleste land støtter at man skal ta med karbondioksid og andre klimagasser. EU går inn for å ta med karbondioksid, metan og lystgass i denne omgang, og flere gasser senere (innen år 2000). Skal sluk som netto tilvekst i skogen kunne tas med? Mange land går inn for å ta med sluk og opptak av karbondioksid gjennom netto tilvekst av skog. For Norge tyder studier referert i det nye Langtidsprogrammet på at 25% av norske utslipp av karbondioksid bindes gjennom netto tilvekst i skogen. Differensiering av forpliktelser Både Klimakonvensjonen og Berlin-mandatet nevner at man skal ta hensyn til landenes ulike utgangspunkt, blant annet m.h.t. økonomisk struktur og ressursbase, for å sikre en rimelig byrdefordeling. En slik løsning kan også bidra til høyere kostnadseffektivitet. I klimaforhandlingene har de landene som har relativt høye kostnader ved å redusere sine utslipp gått inn for differensiering av forpliktelsene. Alternativet med like prosentvise reduksjoner vil bli relativt dyrt for land som Norge, Australia, Island, Japan og Sveits. Utfordringen for de som ønsker differensiering er å enes om prinsipper og kriterier for differensiering, spesielt gitt den begrensede tid som er til rådighet til desember. De viktigste forslagene om differensiering av forpliktelser er: Norge: En gruppe land fordeler utslippsreduksjonen mellom seg basert på tre kriterier, CO2 per capita, CO2 per enhet BNP, og BNP per capita. For hvert land og variabel tas forholdet mellom landet og gjennomsnittet for gruppen. Til sist vektes de tre variablene og summeres. Australia: Kostnaden målt som prosentvis endring i BNP per capita skal være lik i alle land. Fem kriterier legges til grunn for forhandlingene: veksten i BNP, befolkningsveksten, utslipp i forhold til BNP, handel med fossile brensler, og utslipp i forhold til eksporten. Island: Det islandske forslaget er likt det norske, men har med et ekstra kriterium. Dette kriteriet er andelen til fornybare energikilder i energiforsyningen. Japan: Landene kan velge mellom et mål som utslipp per capita eller et mål som en viss prosentvis reduksjon av utslippene i forhold til et basisår. Sveits: Landene skal ha et årlig mål for tillatte utslipp av klimagasser per capita. Utsikter for forhandlingene og Norge Berlin-mandat forhandlingene er vanskelige fordi landene har ulike oppfatninger av hva som er rettferdig. Selv om alle land er opptatt av det globale klima vil landenes posisjoner være farget av nasjonale særinteresser. Forhandlingene blir også vanskelige fordi det ikke finnes et felles akseptert modellverktøy som er egnet til å regne ut økonomiske konsekvenser for hvert land av ulike avtale-utforminger. Kyoto-protokollen blir en balansegang mellom hva som er mulig å få de mest skeptiske landene med på og dens effektivitet til å redusere utslippene av klimagasser. Gjennom å bygge inn ulike typer fleksibilitet i oppfyllingen av protokollen vil det bli lettere å få med de mest skeptiske landene. Fordi det sannsynligvis blir nye forhandlingsrunder etter Kyoto for å revidere klimaavtalene blir det kanskje viktigst å få vedtatt fornuftige prinsipper enn detaljerte og ambisiøse forpliktelser i denne omgang. Utformingen av protokollen blir avgjørende for hva det vil koste for Norge å undertegne den. I utgangspunktet vil en protokoll med ambisiøse mål bli dyrere enn en mindre ambisiøs protokoll. Det beste scenariet for Norge er at protokollen åpner for differensiering, kvotehandel og felles gjennomføring av klimatiltak, en viss fleksibilitet i oppfyllingen av forpliktelser over tid, en kurv av klimagasser, og for sluk for karbondioksid i form av skogtilvekst. Selv om det åpnes for kvotehandel, felles gjennomføring av klimatiltak og sluk for karbondioksid, kan det finnes tekniske problemer som de kan ta flere år å løse. Desto færre av disse ønskene som er oppfylt desto dyrere vil en ellers lik protokoll bli for Norge. Det minst gunstige scenariet for Norge er at protokollen er ambisiøs og få av de norske ønskene blir oppfylt på grunn av motstand fra andre land. En annen mulighet er at viktige land, f.eks. USA, setter bremsene på slik at avtalen blir relativt lite ambisiøs. Dermed blir kostnaden for Norge relativt mindre, men det globale klima mer skadelidende.

A three-dimensional global chemical tracer model and a radiation transfer model have been used to study the role of reduced NOx emissions on radiative forcing. Through production of tropospheric O3, NOx emissions lead to positive radiative forcing and warming. But NOx also reduces the levels of CH4, thereby giving negative forcing and cooling. The lifetime of NOx varies from hours to days, giving large spatial variations in the levels of NOx, and, due to non-linearities in the chemistry, there are also large geographical differences in the effects of NOx on O3 as well as on OH and CH4. We have selected six geographical regions representing different chemical and physical conditions, and the emissions of NOx in these regions are reduced by 20%. The sensitivity in the chemical responses and the radiative forcing due to changes in O3 and CH4 show large variations between the regions. The ozone and methane forcing are of opposite sign and generally of similar magnitude.

Ny teknologi innebærerer normalt bedre løsninger, og har vanligvis positive økonomiske og miljømessige effekter. Bakgrunnen for forslaget om COGEN-anlegget ved Borregaard er imidlertid at en vesentlig del av energitilbudet de idag benytter seg av, produksjonen av svovelsyre, blir borte om få år. Dette har framtvunget nye løsninger. I dette notatet har vi pekt på noen forhold som vi mener er viktige å belyse i en konsekvensutredning av et slikt prosjekt. En evaluering av prosjektet innebærer at en gjennomgår alle aktuelle alternativ og anslår konsekvensene av dem. I noen tilfeller kan ett aktuelt alternativ peke seg ut som det klart beste. Det er da tilstrekkelig å vurdere dette ved siden av det foreslåtte prosjektet. Ofte er det imidlertid flere aktuelle alternativer, og rangeringen av dem kan være avhengig blant annet av hvordan en vektlegger ulike miljømessige konsekvenser. Ved vurdering av de miljømessige konsekvensene av utslipp til luft er det viktig å se på flest mulig utslippskomponenter, og vurdere disse i sammenheng. Dette betyr at endringer i utslipp av ulike komponenter vurderes på bakgrunn av virkningene av eksisterende forurensing og innslaget av langtransporterte forurensninger i regionen. Hvilke bidrag prosjektet gir til langtransporterte forurensninger bør også vurderes. Når det gjelder de globale miljøkonsekvensene må prosjektet og alternativene sees i lys av nasjonale forpliktelser i internasjonale avtaler, eller hvordan globale miljøproblemer kommer til uttrykk ellers i nasjonal politikk. En måte å gjøre dette på er å anslå hvilken avgift bedriften vil kunne tåle å betale for sine utslipp ved den nye teknologien før de går over til å velge et alternativ med lavere utslipp. Dersom denne tenkte avgiften er høyere enn det som med rimelighet kan kreves av alle norske bedrifter, vil det være samfunnsøkonomisk forsvarlig å gjennomføre prosjektet.

Tropospheric ozone changes since pre-industrial times due to changes in emissions have been calculated by the University of Oslo global 3-D photochemical model. The radiative forcing caused by the increase in ozone has been calculated by two independent radiative transfer models; the University of Reading model (Reading), and the University of Oslo/NILU model (OsloRad). Significant increases in upper tropospheric ozone concentrations are found at northern mid-latitudes (15-40 ppbv, depending on season) at about 10 km altitude. In the tropical regions, the largest increase (about 20 ppbv for all seasons) is found at about 15 km altitude. The increase is found to be caused mainly by enhanced in-situ production due to transport of precursors from the boundary layer, with a smaller contribution from increased transport of ozone produced in the boundary layer. The lifetime of ozone in the troposphere decreased by about 35 % due to enhanced concentrations of HO2. The calculated increase in surface ozone in Europe is found to be in good agreement with observations. The calculations of radiative forcing include the effect of clouds and allow for thermal adjustment in the stratosphere. The global and annual averaged radiative forcing at the tropopause from both models (0.28 W/m2 and 0.26 W/m2, for the OsloRad and Reading models respectively) are in the lower part of the estimated range given in IPCC (1995). The calculated radiative forcing is similar in magnitude to the negative radiative forcing by sulphate aerosols, but displaced southward in source regions at northern mid-latitudes. The increase in tropospheric ozone is calculated to have cooled the lower stratosphere by up to 0.9 K, with possibly half of this cooling occuring in the past two to three decades.

As a result of chemical processes in the atmosphere, emissions of NOx can both damp and enhance the greenhouse effect. The two most important effects of NOx in this context are increased concentrations of tropospheric ozone and reduced levels of methane. The ozone response has a warming effect (positive indirect effect) and the methane response gives cooling (negative indirect effect). Previous studies using simplified models have shown that when NOx is emitted from ground sources, these effects may be of the same magnitude on a global scale. It is, however, important to be aware that since they have very different characteristics, these effects do not offset each other. In the free troposphere, the lifetime of ozone is 100-200 days and the changes in ozone and the resulting radiative forcing is limited to a regional scale. Changes in ozone and its radiative forcing occur relatively shortly after the emissions of NOx takes place. Methane, on the other hand, has a lifetime of 10-12 years and changes in methane degradation will therefore affect the concentration of methane on a global scale. The relatively long lifetime also leads to a corresponding time lag in the response of methane compared to changes in NOx emissions. Studies of the effects of NOx have usually focused on the effects of increased emissions. In this project we have studied the chemical and radiative effects of reduced NOx emissions, and how these effects vary among different regions of the world. The following areas have been chosen: Scandinavia, Central Europe, Southern Europe, USA, Southeast Asia, and Australia. In separate model tests the emissions of NOx have been reduced by 20% in each region, and the resulting changes in ozone and methane have been calculated. Changes in the concentrations of these gases have formed the basis for calculation of radiative forcing. In the case of Scandinavia it has been undertaken model tests where emissions of VOC and CO are also reduced. Calculations of the radiative forcing from both ozone and methane have been performed for Scandinavia (two tests), USA and Southeast Asia. The results confirm earlier findings that the indirect effects of NOx through methane and ozone are of the same magnitude, but with opposite signs. We also find that the effects vary significantly in magnitude among the various regions. In addition, we find that in a global and regional perspective, 20% reductions in NOx emissions in Scandinavia have a negligible effect on climate. The magnitude of NOx emissions in the studied regions varies substantially (a factor of 35 between USA and Scandinavia). This is due to differences in area size, population density, as well as economic and technological conditions. USA and Southeast Asia will experience the largest effect of a 20% reduction in NOx emissions on the concentrations of ozone and methane. This is due to the large emissions in USA and the chemical and meteorological conditions in Southeast Asia. Scandinavia separates from the rest by having the smallest effect. The very large differences in changes in NOx emissions in absolute numbers necessitate a normalisation of the effects of changes in emissions; i.e. that changes in ozone and methane are calculated per Tg (1012 g) change in NOx emissions. The same has been done for radiative forcing (given as W/m2/TgN/yr). A ranking of the regions according to changes in the most climate sensitive altitudes of ozone concentrations per reduction in NOx emissions, shows that Southeast Asia is the most sensitive area, followed by Australia. USA and Europe follow thereafter, with Scandinavia ranking slightly below. Concerning radiative forcing resulting from changes in ozone (radiative forcing per reduction in TgN), Southeast Asia is about 8 times more sensitive than Scandinavia, while USA is about 20% more sensitive. We find that the sensitivity of radiative forcing due to increased methane concentrations is about 6 times higher for NOx reductions in Southeast Asia than for NOx reductions in Scandinavia. The sensitivity of NOx reductions in the USA is about 30% higher than in Scandinavia. While the climate effect of a 20% reduction in NOx in Scandinavia is negligible, the radiative forcing of reductions in ozone resulting from a 20% reduction in NOx emissions in the USA is significant. However, if indirect radiative forcing of NOx reductions is given per unit reductions in NOx emissions, the estimates indicate that the sensitivities of radiative forcing from ozone and methane in Scandinavia and USA are comparable. The estimates also show that changes in the emissions of other gases are very important. Model experiments that at the same time reduced the emissions of VOC and CO in Scandinavia by 30% (test 2) resulted in a radiative forcing of around 60% lower (less negative) than if only NOx emissions were reduced. The reason for this is that oxidation products from these gases take part in chemical reactions that remove ozone when NOx levels are sufficiently low. This fact underlines the need for considering various measures for emission reductions jointly and to analyse how measures affect several gases simultaneously. A model experiment was also undertaken where emissions of VOC, CO and NOx were reduced by 30% in Scandinavia (test 3). The results showed only minor deviations from test 2 (20% reduction in NOx and 30% reduction in VOC and CO), but on a global scale the effect on ozone was somewhat lower in test 3. This is a result of complex relationships in the atmospheric chemistry as well as varying impacts of transport on the distribution of gases that leads to ozone formation. Reduced levels of NOx and O3 and hence lower concentrations of OH in one region result in lower oxidation of CO and hydrocarbons. This in turn increases the supply of these ozone precursors in areas further south, and enhances the ozone levels there. Because of the complex role of NOx in the chemistry of the atmosphere as well as large spatial and temporal variations in the NOx concentration, there are significant uncertainties associated with calculations of changes in ozone and methane. This implies that, at present, it is not possible to give any firm conclusions regarding the net effect of NOx on the radiative forcing, since the warming and the cooling effects are of the same magnitude. Estimations of net effects of NOx may be of limited value as the radiative forcing of ozone and methane have different characteristics and may lead to different effects on the atmospheric circulation patterns. Despite the uncertainties concerning quantification of indirect climatic effects of NOx emissions, several studies support our conclusion that NOx both has warming and cooling effects and that these probably are of the same magnitude. In order to study the chemical responses on changes in NOx emissions, we have used a global 3-dimensional model (longitude x latitude x elevation) with an extensive chemistry scheme as opposed to previous studies that used 2-D models. Radiative forcing resulting from changes in ozone is calculated by professor Wang and his group at the State University of New York at Albany, USA.

Dette er en oversettelse av synteserapporten fra den andre hovedrapporten til FNs klimapanel (IPCC). Synteserapporten drøfter vitenskapelig og faglig informasjon med relevans for fortolkning av Artikkel 2 i FNs rammekonvensjon om klimaendringer (FCCC). På grunn av hensynet til vitenskapelig presisjon har vi så langt som mulig fulgt ordlyden i den engelske originalteksten. Dette har i noen tilfeller gått på bekostning av leservennligheten. I tillegg har CICERO foran i rapporten laget en mer kortfattet beskrivelse av IPCC og noen sentrale konklusjoner fra IPCCs andre hovedrapport. Arbeidet er utført av CICERO på oppdrag fra Miljøverndepartemenet. Følgende personer har vært involvert: Terje Berntsen, Jan Fuglestvedt, Ivar Isaksen, Mariann Murvoll, Lars Otto Næss, Tora Skodvin og Asbjørn Aaheim. Vi vil takke for nyttige kommentarer og innspill fra Øyvind Christophersen og Harald Dovland (Miljøverndepartementet), Frøydis Kvaløy (Direktoratet for Naturforvaltning), Lorents Lorentsen (Finansdepartementet) og Thomas Martinsen (Statens Forurensningstilsyn).

The study reviews and analyzes some major issues that must be considered when defining principles for distributing commitments to reduce greenhouse gas emissions for countries belonging to the Organization for Economic Cooperation and Development (OECD). The study is divided into three main parts, where the first discusses the concept and measurement of costs, the second analyzes the negotiations and burden sharing rules, and the third analyzes the handling of a mix of greenhouse gases. The study shows that removal of subsidies on fossil fuels or minimum fossil-fuel taxes have advantages in terms of cost-effectiveness and fairness compared to quantified national reduction commitments. The calculations suggest that a moderate climate policy is optimal, but a more ambitious climate policy is favorable if emissions abatement is relatively inexpensive or climate-change effects are uncertain. The burden sharing rules examined have quite different consequences for the OECD countries depending on the choice of rule and weights of the criteria included. Due to the lack of reliable methodologies and uncertainties in the understanding of the mechanisms of some gases, not all climate gases should be included in the negotiations.

The principle of comprehensiveness constitutes an important element in the climate convention, but guidelines as to how this principle is to be understood and implemented are not provided. In this analysis the meaning of this concept within the context of climate change is investigated: How should "comprehensiveness" be defined and operationalized and which scientific considerations need to be taken into account? Understood as an approach by which all greenhouse gases are juxtaposed and parties are permitted to choose their individual reduction paths within a common framework, the comprehensive approach may constitute an important element in the development of adequate solution design models for a climate regime. The study discusses the criteria necessary for deciding which gases to include in a comprehensive approach, and, based on these criteria, a set of gases is proposed. The study also examines the requirements a method for comparing gases with different properties must fulfill in order to be able to employ a comprehensive approach as proposed. Estimations of the relative contribution of a particular gas to the enhanced greenhouse effect is very dependent upon the chosen time horizon. Moreover, the choice of horizon is linked to the kind of effect with which one is concerned. Thus, the selection of the time horizon is a choice with significant environmental and policy implications. Determining time horizons may prove to be a difficult one, and should be handled with care within the scientific, technical and political bodies of the climate convention. There may be a lot to gain politically by adopting and developing a comprehensive approach, although it should be emphasized that a comprehensive approach may complicate, and most probably prolong, the negotiation process. There is a set of difficult questions which have to be settled among contracting parties in order for this approach to work as intended.

The aim of this report is to analyze the conditions under which Joint Implementation (JI) can contribute to a costeffective abatement of global greenhouse gas (GHG) emissions. JI refers to policies and measures implemented jointly by Parties to reduce net GHG emissions contributing to meeting their national commitment under the Climate Convention. The overall conclusion is that JI is a promising mechanism under some circumstances. Difficulties related to implementation and control of JI projects vary considerably and depend on what countries participate, how the project affects GHG emissions or sinks (for example through fossil fuel saving or through carbon sequestration in forests), and the institutional frames for JI. The Conference of the Parties (COP) to the Climate Convention should take steps to establish the institutional capacity necessary to initiate and coordinate a number of studies and pilot projects in regard to JI. The potential problems related to implementation and control of the simplest JI project type are also found for the more complicated JI project types. Thus extra effort should be put into solving these basic issues. Contracts between JI parties should include incentives for the host country to implement the project in an efficient manner. Contracts can reduce some of the problems that may lead to a reduced cost saving potential and difficulties in controlling the global GHG abatement effect of JI projects. The establishment of a Clearinghouse or Credits Bank institution may significantly reduce some of the potential problems related to implementation and control of JI projects. These problems include asymmetric information and incentives that generate inefficiencies, the difficulties involved in measuring the global abatement effect of a JI project, and handling of risk related to uncertain cost per unit of GHG abatement.

Global Warming Potentials for emissions of CH4, CO and NOx that take into account indirect chemical effects have been estimated for five time horizons. The indirect effects of methane emissions that have been considered are the ability of methane to increase its own lifetime (through the CH4/OH-feedback) and the effects on the levels of tropospheric ozone and stratospheric water vapour. All these effects have Positive signs, and our estimate shows that the indirect effects together are of the same magnitude as the direct radiative effect of methane. For emissions of NOx, the picture is somewhat more complicated. Emissions of NOx generally increase the levels of tropospheric ozone. Ozone is an important GHG and therefore this mechanism constitutes a positive indirect effect. On the other hand, NOx emissions increase the levels of OH, thereby reducing the lifetime of gases that are removed by OH. Of these, methane is the most important in this context. The effect on CH4, through changes in OH, constitutes a negative indirect effect on climate. Difficulties may therefore be connected to estimating the net effect of these opposing effects. However, for NOx emitted from airplanes the radiative forcing from changes in ozone is significantly larger than the radiative forcing from the changes in methane. We may therefore conclude that the net effect of NOx emitted from aeroplanes is positive. Our estimates also indicate that the climate impact of NOx emissions from aeroplanes, expressed as GWPS, is relatively large. One should, however, bear in mind that while the GWPs for NOx from aeroplanes are relatively large, the emissions are small compared to the surface emissions of this component. For NOx emitted from surface sources the picture is not so clear. Contrary to the emissions from aeroplanes, surface emissions of NOx affect OH in a region of the troposphere that is very important for the oxidation of CH4. The negative effect through reduced CH4 levels are therefore more important than in the case of NOx emitted from aeroplanes. The estimated net effect is slightly negative since the positive effect through increased O3 levels is somewhat smaller than the negative effect. This estimate may be model dependent and should only be considered a preliminary finding. Emissions of CO increase the tropospheric levels of ozone, and, through lowered levels of OH, CO increases the levels of methane. Thus, the considered indirect effects of CO are positive. The effects of NMHC emissions on the radiative balance are assessed by comparison with the effects of CO. This assessment is dependent on the chemical composition of NHMC. In the IPCC assessment from 1992, only the direct GWPs for methane were given and the estimates of the indirect GWP from the 1990 assessment were abandoned. In IPCC 1990, GWPs for NOx from surface sources were also given, but only the effect through increased levels of tropospheric ozone were considered. This estimate was also left out in the 1992 report. There are large uncertainties connected to the estimates of the indirect GWPS. The estimated GWPs represent what we are able to infer with the present model tools, and they should be considered as preliminary results which will change. Efforts should be made to develop these model further and to refine the methods for estimating the GWPS. The GWPs for CF4 and C2F6 given in this current report are also different from earlier estimates (WMO, 1992 and EPCC, 1992). The estimates are taken from Isaksen et al. (1992b), and a summary of the present state of knowledge in this area is also given. In addition, a short review of the knowledge of SF6 is also given. CF4 , C2 F6 and SF6 , all have very long atmospheric lifetimes and strong absorbtion of IR, giving very high GWP values.

A two-dimensional chemistry/transport model of the global troposphere is used to study the chemical response to i) increased UV-radiation from stratospheric ozone depletion and ii) increased temperatures and water vapour densities that follow from in-creased levels of greenhouse gases. Increased UV radiation increases the photolysis rates for several tropospheric gases, in particular ozone. This leads to enhanced levels of odd hydrogen and reduced concentrations of tropospheric ozone. Increases in temperature and water vapour densities reduce the levels of tropospheric ozone through temperature dependent reaction rates and increased production of odd hydrogen. In both cases the methane levels are also reduced. Thus, the results indicate that the considered mechanisms constitute damping effects on global warming. For a global temperature increase of 3.88 K, the levels of tropospheric ozone and methane are reduced by about 10% and 18%, respectively.

Country studies are important instruments for determining national climate policies and adding to the global knowledge on climate issues. They are, however, also the basis for examining the obligations of the Parties under the United Nations Framework Convention on Climate Change (FCCC), and for developing and assessing projects eligible for financing by the Global Environmental Facility (CEF). It is important that these country studies are comparable, in order to make the CEF efficient and able to compare and choose between projects built on country studies, in terms of their ecological and economic efficiency. The term "country study" should in our context be understood as an official national study on climate change which could include parts or all of the following areas: inventories of sources and sinks; impacts and vulnerability assessments; and response strategies and options, both on adaptation and greenhouse gas (GHG) abatement. This report is prepared for the Administrator of the Global Environmental Facility (CEF), as a basis for discussion at a workshop organised by TERI in New Delhi in February 1993 on improving current approaches to country studies on climate change. It is also a contribution to the discussion within the Program for Measuring Incremental Costs in the Environment (PRINCE). The CEF commissioned CICERO on November 20,1992, to study experience to date, drawing explicitly upon those studies funded under CEF as well as experiences from other studies. As many of the studies are not yet completed, the focus of this review is on work plans, terms of reference and underlying assumptions and parameters used in their development. Ideally this work should also include interviews with the institutions involved in the preparation of such studies. The time available has, however, not permitted us to meet this objective. The terms of reference of the review states that the following elements should be considered, of which the area of costing exercises was highlighted: (i) an assessment of the level of activity currently and projected in the field of country studies on climate change, including an inventory of studies underway or planned; (ii) a review of the terms of reference for such studies including a review and assessment Of.. -their objectives; -methodological approaches; -parameters and assumptions used, including treatment of discount rate, costing assumptions, abatement targets etc.; -range of policy and investment/expenditure options to be reviewed and assessed; and -the extent to which local staff were involved in design and implementation of these studies; (iii) a review of the costs and staffing patterns Of such studies including the expertise required to undertake specific studies; and (iv) for those studies completed or underway, an assessment of their usefulness for government policy makers, especially in terms of providing a clear strategy for future activities including provisions and "expectations" laid down in the climate convention. The availability of completed studies and terms of reference for such studies was meagre. This review and assessment is, therefore, built on a very limited number of studies and terms of references, as listed in Annex 1. The time available for the preparation of this first draft has also limited our ability to study in depth all the issues mentioned above. We trust, however, that this exercise is a valuable start and may assist in the discussions and the development of more comparable methodologies for country studies. Contents : Chapter 1 is an overview of the current and planned activity in the field of country studies. Chapter 2 introduces important elements of inventories on sources and sinks of GHG, and focuses on these inventories in terms of methodological approaches, documentation and reporting. Chapter 3 is concerned with impact and vulnerability assessments, and starts with a discussion of the basis upon which impacts may be estimated. This is followed by an assessment of country studies in terms of physical and biological effects, and in terms of economy. Chapter 4 consists of four main parts: the theoretical platform for cost-benefit analyses related to climate change interventions; a discussion of a practical approach; an evaluation of country studies; and possible improvements of current approaches. Chapter 5 is a review of the costs and staffing patterns in the same studies. Chapter 6 is a discussion of the usefulness of country studies for government policy makers in their efforts to meet their obligations under the Framework Convention on Climate Change.

A two-dimensional (altitude vs. latitude) photochemical/transport model of the global troposphere is applied to study the effects of changed emissions of NOx, CH4, CO2 and NMHC on the levels of O3, OH and CH4. On a mass basis, the efficiencies in increasing O3 concentrations differs markedly between the source gases, with NOx having the largest effects. The sensitivity to increased emissions of NOx from airplanes is found to be significantly higher than for ground emissions of NOx (> a factor of 10). The tests also show that the efficiencies are larger for smaller perturbations and that the background levels of NOx are important for the efficiency in O3 enhancement from NOx emissions. Increased emissions of CO2, CH4 and NMHC all reduce tropospheric OH, while increased NOx emissions increase OH. Through changes in OH these source gases also affect the distribution of CH4. Since increased emissions of CH4 reduce the strength of its own main sink, the relative increase in atmospheric levels is larger than the relative increase in emissions. The strength of this positive feedback is estimated to be approximately 35The results indicate that the indirect effects of emissions of CH4, CO2 and NMHC on climate may be positive due to the positive effect on O3 and the negative effect on OH, with the latter effect increasing the lifetimes of greenhouse gases removed by OH. The indirect effects of NOx on climate are of opposite signs; a positive through O3 increases and a negative through OH increases. Thus, estimates of the net effect of the indirect effects of NOx emissions on climate require better knowledge of the NOx distribution and detailed radiative calculations.

The observed reductions in stratospheric ozone since the late 1970s are likely to have affected the penetration of UV radiation into the troposphere. We have examined the sensitivity and the response of the tropospheric chemistry to such changes in UV radiation. Based on observations of ozone column densities and model calculations of changes in the ozone column densities after 1970, photodissociation rates for selected years (1970, 1980, 1990, 2000 and 2050) are calculated. These calculations give significant changes in the dissociation rates of some gases, particularly in the dissociation rate for O3 yielding O('D). This increase in photodissociation rates initiates increases in tropospheric OH. However, the model studies show that the OH changes are somewhat damped compared to the changes in short wave radiation due to strong interactions between key species in the troposphere. Ozone is reduced in most areas when the UV radiation increases, but the percentage reductions in ozone are significantly smaller than the percentage UV increases. However, during spring, O3 increases in regions where NOx is enhanced. The calculations give increased levels of H2O2, although the magnitude of the response varies considerably with time of year and with region, and they are largest at high latitudes during spring. The relative changes in methane are found to be less than the relative changes in global average of OH since the largest relative OH changes take place outside the region of most importance for the methane oxidation (low latitudes and low altitudes). In addition, the effect is delayed in accordance with the chemical lifetime of methane (~10 years). The results indicate that increased fluxes of UV due to reduced ozone columns may have contributed to the reduction in the growth rate of methane, and the magnitude of this effect is estimated to ~1 /3 of the reduction. It is therefore unlikely that changes in UV fluxes is the main cause of the reduction in the growth rate of methane which has been observed during the 1980s. The mechanism constitutes a negative indirect chemical effect on climate from the ozone depleting substances, mainly the CFCS. Det er observert reduksjoner i stratosfærisk O3, hvilket har økt innstrålingen av UV til troposfæren. UV-strålingen driver den kjemiske omsetningen i troposfæren, og ved hjelp av modeller og observasjonsdata studeres kjemiske responser på UV-økning. Resultatene viser betydelige økninger i fotolyserater, spesielt i fotolysen av O3 som initierer produksjon av OH; den viktigste oksidanten i troposfæren. Men pga. interaksjoner i kjemien blir denne økningen noe dempet. Nivåene av troposfærisk O3 reduseres, bortsett fra i vårmånedene i områder med høye NOx konsentrasjoner, der en får en viss økning. H2O2 viser markerte økninger som varierer sterkt med årstid og breddegrad. Beregningene indikerer også at de økte OH-nivåene fører til reduserte veksthastigheter for CH4-konsentrasjonen, men at dette bare kan forklare ~1/3 av den observerte reduksjonen. Siden KFK bryter ned stratosfærisk O3 har disse gassene negative indirekte effekter på klimaet via de studerte mekanismene.