1.1 Background 1. INTRODUCTION This Technical Paper was produced at the request of the Subsidiary Body for Scientific and Technological Advice (SBSTA) of the Conference of the Parties (COP) to the United Nations Framework Convention on Climate Change (UN/FCCC). At its second session (Geneva, 27 February-4 March 1996) SBSTA requested IPCC to provide an assessment of the implications for projected temperature increases, sea level rise and other changes in climate of different proposals for the limitation of greenhouse gas emissions? by Annex I Parties 34. The IPCC Bureau approved the production of a Technical Paper in order to meet this request at its tenth session (Geneva, 28-29 March 1996). An initial problem with the preparation of a useful Technical Paper on this subject was that none of the emissions limitation proposals tabled at that time extended beyond the year 2010. For carbon dioxide (CO2), even with large emissions differences in 2010, differences in CO2 concentration, global mean mperature and global mean sea level in 2010 will be comparatively small because of the slow responses of atmospheric CO2 and the climate and sea level systems to emissions changes. The consequences of greenhouse gas emissions changes, and CO2 emissions changes in particular, take decades to centuries to manifest themselves fully in the climate system. Thus, in order to carry out useful climate and sea level calculations it is necessary to have information that extends beyond just a few decades. A set of extended emissions limitation scenarios were therefore required to enable the analysis to be carried out. It was decided during the twelfth session of the IPCC (Mexico City, 11-13 September 1996) that, to generate information beyond 2010, further guidance was required from SBSTA. SBSTA considered the issue at its fourth session (Geneva, 16-18 December 1996). By this time, additional emissions limitation proposals had been tabled, compiled in the 31 January 1997 document from the Ad hoc Group on the Berlin Mandate (AGBM) entitled "Framework Compilation of Proposals for Parties for the Elements of a Protocol or Another Legal Instrument (FCCC/AGBM/1997/2)”. It is scenarios 1 Hereafter terms with the symbol can be found in the Glossary (Appendix 4) 2 Such proposals fall under Article 17 ("Protocols") of the FCCC. We refer to them here as "emissions limitation proposals". These include both the proposals for Annex I countries to limit emissions (as compared to baseline projections) as well as the proposals for absolute reductions of emissions compared to 1990 by Annex I countries. The term Quantified Emission Limitation and Reduction Objectives (QELROS) used by the FCCC has the same meaning, but is less transparent to the general reader. The term "protocol" is not used because this has a broader meaning. 3 In this Technical Paper, we frequently use the word "countries" to refer to the FCCC term "Parties to the Convention". drawn from these proposals that are studied in more detail in this Technical Paper. In FCCC/AGBM/1997/2 two Parties (France and The Netherlands) made proposals that were openended in time-scale. These proposals are suitable for use in a study of the climate and sea level implications of emissions limitations by Annex I countries and, hence, are used as a primary basis for the study in this Technical Paper. Since the first draft (16 April 1997) of this Paper was written, submissions relevant to this Technical Paper were received from seven Parties to the FCCC (contained in FCCC/SBSTA/ 1997/MISC2, dated 19 February 1997). These express divergent views on the emissions scenarios to be used. At its fifth session (Geneva, 24-28 February 1997), SBSTA "requested the IPCC to take into account and where appropriate reflect these contributions" in the development of the present Technical Paper (see FCCC/SBSTA/1997/4, paragraph 26(n), dated 7 April 1997). These submissions have been considered. Subsequent to this, in an Addendum to the report of the AGBM's sixth session (Bonn, 3-7 March 1997) "Proposals for a Protocol or Another Legal Instrument -- Negotiating Text by the Chairman" (FCCC/AGBM/1997/3/Add.1), dated 22 April 1997, there are a number of new proposals and withdrawals. In order to be as responsive as possible to the negotiating process we have therefore included, in Appendix 1, a summary of these latest proposals and how they relate to the emissions limitation proposals studied in more detail in this Technical Paper. 5 Article 2 states that "The ultimate objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner." It should be noted that one of the requirements for IPCC Technical Papers is that they must be based solely on material already in the IPCC assessment reports and special reports. The results presented here are therefore consistent with these earlier reports. It should also be noted that, while all the emissions limitation proposals refer only to Annex I countries as agreed upon in the Berlin Mandate (FCCC/CP/1995/7/Add. 1, Decision 1/CP.1), dated 6 June 1995, in order to be able to carry out an analysis for global CO2 concentrations and climate implications it is necessary to use global emissions. Since there are no formal proposals for limitations on emissions from non-Annex I countries, we derive these global values by combining Annex I country emissions under the various limitation proposals with emissions for non-Annex I countries from the "no-climatepolicy" IS92a, c, and e scenarios (see Box). The emissions limitation proposals used in this Paper are expressed variously in terms of CO2 only or in terms of greenhouse gases. For the purposes of this Paper all the proposals are interpreted as applying to fossil CO2 emissions§7 alone. The reasons for using this approximation are given in Section 3. Implications of Proposed CO2 Emissions Limitations To fully meet the initial request of the SBSTA (i.e., to discuss the temperature and sea level implications of the emissions limitation proposals) in a comprehensive manner, it would be necessary to cover the full range of possible concentrations (taking into account sinks and sources) of other gases such as methane (CH4), nitrous oxide (NO), tropospheric ozone (03) and the halocarbons, along with the full range of possibilities for sulphate aerosols derived from sulphur dioxide (SO2) emissions. Such an analysis is beyond the scope of this Paper. Further discussion of the effects of various scenarios for other gases and sulphate aerosols is given in IPCC Technical Paper 38 (Schimel, et al., 1997). 6 An alternative but equivalent way to derive global emissions is to first determine the emissions reductions for Annex I countries that result from a particular emissions limitation proposal (this will depend on the IS92 scenario that the limitation proposal is compared with), and to subtract this from the global emissions for the same IS92 scenario. 7 Fossil CO2 emissions are those arising from fossil fuel combustion (including gas flaring) and cement production. 8 Hereafter referred to as TP3: similarly, TPI and TP2. IS92 emission scenarios The six IPCC scenarios, IS92a-f. (Leggett, et al., 1992). Supplementary Report to the IPCC Scientific Assessment, hereafter referred to as IPCC92) embody a wide array of assumptions affecting how future greenhouse gas emissions might evolve in the absence of climate policies beyond those already adopted. A summary of the economic growth, energy supply and population projection assumptions made in deriving these scenarios is given in Table 4. The IS92 scenarios take into account: (a) The London Amendments to the Montreal Protocol; (b) Population forecasts of the World Bank and United Nations; (c) The report of the Energy and Industry Subgroup of the IPCC (IPCC-EIS, 1990); (d) Political and economic changes in the former Soviet Union, Eastern Europe and the Middle East; and (e) Data on tropical deforestation and sources and sinks of greenhouse gases. Overall, the scenarios indicate that greenhouse gas emissions could rise substantially over the coming century in the absence of new and explicit control measures. IS92a and IS92b: These scenarios give emission estimates that are intermediate compared with those of the other IS92 scenarios. The major difference between IS92b and IS92a is that IS926 takes into account information available up to 1992 on the commitments of some OECD countries to stabilize their CO2 emissions. IS92c: This scenario assumes the lowest rate of population and economic growth and severe constraints on fossil fuel supplies. As a result, it is the lowest emission scenario and the only one showing a decreasing emission trend. IS92d: This scenario employs the low population growth rate of IS92c but a higher economic growth rate, hence it has the second lowest future emission estimates. IS92e: This scenario assumes intermediate population growth and high economic growth rates with plentiful fossil fuels. Consequently, this scenario has the highest estimates of future emissions. IS92f. This scenario uses the highest population estimates of the IS92 scenarios, but lower economic growth assumptions. It is the second highest emission scenario. Revised versions of these scenarios are currently being produced by IPCC and will be published as a special report. Concentration When the FR or NL emissions limitation proposals for Annex I countries are combined with IS92 scenarios for nonAnnex I countries, projected CO2 concentrations are less than under any of the IS92 scenarios. The concentration reductions relative to the IS92 scenarios (with the exception of IS92c) eventually become substantial, of the order of 100 ppmv by 2100 for IS92a and 200 ppmv by 2100 for IS92e. Stabilization None of the emissions limitation proposals would lead to anything approaching CO2 concentration stabilization when non-Annex I country emissions are assumed to follow the IS92a or IS92e scenarios. In these cases, CO2 concentrations range between approximately 575 and 950 ppmv and are still increasing rapidly in the year 2100, at twice (IS92a) and five times (IS92e) the present rate of increase. • By 2100, CO2 concentrations would show a clear tendency towards stabilization if non-Annex I country emissions were to follow the IS92c scenario, the lowest of the IPCC emissions scenarios, and Annex I countries were to follow this scenario or any of the FR or NL emissions limitation proposals. The previous two key results imply that, for the cases studied, unless population growth, economic growth, technological change and other factors combine in such a way that global emissions mimic the low-emission IS92c scenario, substantial global emissions reductions beyond those defined by the various emissions limitation proposals would be required. • Any eventual stabilized concentration is governed more by the accumulated anthropogenic3 CO2 emissions from now until the time of stabilization, than by the way those emissions change over the period. This means that, for a given stabilized concentration value, higher emissions in early decades require lower emissions later on. The effects of emissions limitation proposals accrue only Temperature and Sea Level • Future CO2 concentration projections are subject to uncertainties arising from our incomplete understanding of the carbon cycle. However, uncertainties in the reductions in radiative forcing arising from the emissions limitation proposals are smaller. This is because the cumulative emissions reductions due to the limitation proposals are small relative to the total cumulative emissions, and because of the non-linear relationship between CO2 concentration and radiative forcing. • The emissions limitations proposals considered here affect future changes in global mean temperature and sea level. By 2100, relative to the no-limitation cases, the reduction in global mean temperature increase resulting from the NL-2% limitation proposal ranges between 0.1°C (i.e., from 0.7°C down to 0.6°C for IS92c and a climate sensitivity of 1.5°C) and 0.9°C (i.e., from 3.9°C down to 3.0°C for IS92e and a climate sensitivity of 4.5°C), while the reduction in sea level rise ranges between 2 cm (ie., from 12 cm down to 10 cm for IS92c and a climate sensitivity of 1.5°C) and 15 cm (i.e., from 100 cm down to 85 cm for IS92e and a climate sensitivity of 4.5°C). • While temperature and sea level results are given in detail only for the NL-2% case, the reductions in the increases in these variables achieved by any given year can be easily generalized to other smoothly-varying emissions limitation scenarios. 3. DESCRIPTION AND QUANTIFICATION OF EMISSIONS LIMITATION PROPOSALS As noted in the Introduction, the emissions limitation proposals for Annex I countries examined in this Technical Paper are documented in the 31 January 1997 report of the AGBM entitled "Framework Compilation of Proposals from Parties for the Elements of a Protocol or Another Legal Instrument" (FCCC/AGBM/1997/2, pp. 34-39). The details (for those suggestions that may be fully defined in quantitative terms) are summarized in Table 1 and expressed in terms of absolute CO2 emissions in Table 2. In producing Table 2, emissions limitation suggestions expressed in terms of greenhouse gases (rather than CO2 specifically) have been interpreted as applying to fossil CO, emissions alone. If such limitations were achieved through emissions reductions of nonCO2 greenhouse gases in addition to, or in place of, CO2 emissions reductions (ie., in accordance with the so-called "comprehensive" approach noted in Article 3.3 of the FCCC), then higher CO2 emissions than those assumed here would be possible. However, if the emissions limitation proposals were expressed in CO2-equivalent terms (e.g., see TP3. Section 2.2) in an appropriate way, then the temperature and sea level results produced here would apply equally to the CO-alone and greenhouse gas (CO-equivalent) cases. In the absence of any suggestions for the breakdown between CO2 and non-CO2 emissions reductions, and because there is no agreed method of satisfactorily quantifying the effects of non-CO2 emissions reductions in CO,-equivalent terms?, it is not possible to easily quantify the additional CO2 emissions that a comprehensive approach might allow. The emissions limitation proposals listed in Table 2 assume that Annex I country emissions levels in the year 2000 are the same as in 1990. This is in accordance with Article 4.2(a) and (b) of the FCCC. It is also assumed in all cases that CO2 emissions for Annex I countries remain constant over 1990-2000. If the limitation proposals remain unchanged after the year 2000, the effects of these simplifications on the calculated CO2 concentrations are very small. Should emissions for Annex I countries rise during the 1990s, then fall to the 1990 level in the year 2000, the increase in concentration in the year 2000 would be approximately 0.4 ppmv for every additional GtC of CO2 emissions accumulated over 1990-2000 declining to 0.2 ppmv per additional GtC by 210010. Within the range of possible emissions for the 1990s, this effect on concentration is negligible. 9 Global Warming Potentials (GWPs) provide a means of comparing the effect of different greenhouse gases with that of CO2. However. the values of the GWPs for a given gas differ greatly depending on the time horizon which is chosen. Therefore GWPs can only be used to provide an approximate measure of CO2 equivalence associated with a specific choice of time horizon. 10 The same sensitivity to emissions "errors" over 1990-2000 applies to global emissions. In other words, if global emissions over 1990-2000 differ from the values assumed here, then the effect would be a change in concentration of 0.4 ppmv for each cumulative GtC of emissions "error" in the year 2000, declining to 0.2 ppmv by the year 2100. Emissions limitation proposals for Annex I countries Reduce CO2 emissions by at least 20 per cent by 2005 Reduce CO2 emissions by 10 per cent by 2005, and by 15-20 per cent by 2010 Reduce CO2 emissions by 10-20 per cent by 2010 Reduce CO2 emissions by 20 per cent by 2005, and by 50 per cent by 2030 Reduce ghg emissions by 5-10 per cent by 2010 Return ghg emissions to 1990 level by 2000, reduce emissions by 10 per Reduce ghg emissions by an average of 1-2 per cent per year (from 2000) Table 1. Description of emissions limitation proposals for Annex I countries (FCCC/AGBM/1997/2, dated 31 January 1997). All reductions are relative to the 1990 level. Some proposals apply to CO, alone, others to CO2 plus other greenhouse gases (ghg) presumably in some equivalent CO2 emissions sense. Note that, in general, FCCC usage of the term ghg excludes gases controlled by the Montreal Protocol. |