Understanding IPCC 1992 report's emission scenario

Introduction
The fifth session of Inter-Governmental Planning on Climate Change(IPCC)(Geneva, March 1991) distributed six tasks among three working groups. The particular responsibility of the sixth task, which was emission scenario analysis, fell on Working group 1(WG1). The emission scenario analysis was a particularly complex document as it included multiple previous study analysis and constant new detailed descriptions of emission. On 1992, IPCC released a full supplementary report that included emission scenario.

The Atmospheric stabilising framework(The tool)
This framework principally involves balancing the supply and demand of the global energy system. It combines emission from different sectors. For example energy, industry, agriculture, forest and land-use. Each sector merges assumptions concerning future population, economic growth, resource availability in future, etc. It estimates emission for CO2, CH4, N2O, CFCs and substitutes CO, NOx, Volatile organic compound(VOCs) and SOx. There are four major sectors i.e. energy, agriculture, CFCs and tropical forest sector.
The energy sector uses energy price to equalize demand of four energy end sector and supply from diverse sources. The increased energy price influences the increase in alternative or additional souces and increases energy efficiency, but has a minute impact on economic growth.
The agriculture sector uses predictions on population growth, economic growth and enhanced yields to predict production and consumptions of agricultural products, land and fertilizer use along with greenhouse emissions.
The CFC sector expects to estimate future emissions of CFC, HCFCs, HFCs, methyl chloroform and CCl4 by taking into consideration various policies and its effective implementation.
The tropical rainforest sector gathers assumption regarding the increase in population, more agricultural land required, the procedure of forest clearing and amount of carbon accumulated by the land cover to estimate emissions.

General assumptions
Earlier there was a document SA90 a possible emission report by IPCC in 1990. Six more possibilities were added during this report. The future population assumptions came from World bank report. Since then the world bank revised and UN published new population estimation. UN alternative scenarios are also included in this report that involves more extreme estimation from the upper and lower end.

Scenario-IS92a
This scenario assumes the population to be 11.3 B by 2100 and economic growth from 1990-2025 be 2.9% and from 2025-2100 be 2.3%. Energy supply involves 12,000EJ from conventional oil, 13,000EJ from natural gas, 191EJ from biofuels @ $70/bbl and solar cost falls to $0.075/kWh. Other compliance to agreement involves incorporating the London Amendments to the Montreal Protocol, the amended US Clean Air Act, and the SOx, NOx, and VOC Protocols of the Convention on Long-Range Transboundary Air Pollution (LRTAP). Regarding CFCs, it was assumed a gradual phase-out of CFC by 2075 by non-attendants of Earth summit and limited compliance with Montreal protocol.

IS92b
Scenario assumptions regarding population, economic growth and energy supply were the same as 'a'. Other agreements were also the same as ‘a’ plus OCED members commitments to stabilise CO2 emission. CFC emission global agreement with scheduled Montreal Protocol elimination.

IS92c
This scenario assumes the population to be 6.4 B by 2100 and economic growth from 1990-2025 be 2.0% and from 2025-2100 be 1.2%. Energy supply involves 8,000EJ from conventional oil, 7,300EJ from natural gas and nuclear cost decline by 0.4% annually. Other agreements and CFCs emissions were the same as ‘a’.

IS92d
This scenario assumes the population to be 6.4 B by 2100 and economic growth from 1990-2025 be 2.7% and from 2025-2100 be 2.0%. Energy supply involves 8,000EJ from conventional oil, 7,300EJ from natural gas, the solar cost falls to $0.065/kWh and 272EJ from biofuels @ $50/bbl. Other agreements involve emission controls extended worldwide for CO, Nox, NMVOC and Sox. Capture and use of emissions from coal mining and gas production and use. Cease deforestation. CFC production phase-out by 1997 for industrial countries. Phase-out of HCFCs.

IS92e
This scenario assumes the population to be 11.3 B by 2100 and economic growth from 1990-2025 be 3.5% and from 2025-2100 be 3.0%. Energy supplies include 18,400EJ conventional oil, 13,000EJ Natural gas and phase-out of nuclear by 2075. Other agreement is emission control which increases fossil energy costs by 30%. CFC emissions are the same as ‘d’.
IS92f
This scenario assumes the population to be 17.6 B by 2100 and economic growth from 1990-2025 be 2.9% and from 2025-2100 be 2.3%. Energy supply 18,400EJ from conventional oil, 13,000EJ from Natural gas, the solar cost falls to $0.083/kWh and nuclear costs increase to $0.09/kWh. Other agreements and CFCs emissions were the same as ‘a’.

Table of assumptions used in deforestation cases

Table of emission

Cumulative net Carbon emission

Comparison and other studies 
IPCC has not conducted a probability exercise of the prospective scenario but other studies have been analysed for the best guess scenario. Uncertainty analysis for carbon emission from fossil fuel was done in two studies, Edmonds et al. (1986) and Nordhaus and Yohe (1983). Further deep explanation on the energy consumption, intensity and future specific requirements are discussed in the study thoroughly. This study also explains different scenarios regarding halocarbons and policies affecting its emissions. Details of agriculture, forest and land conversion have also been included precisely.

Important uncertainty in scenario

1. The large human evolutionary patterns are diverse like economic, environmental and technological advances or institutional concerns and are mostly inter-related.
2. The deficient scientific knowledge partly regarding emission factors and their relationship. Another possible limitation of this study is that does not charge the effects of climate change on agricultural production, energy demand and terrestrial ecosystem.

Conclusion

The purpose of this study was not to foresee future greenhouse gases estimation but to help policymakers to consider the direction in which emissions might unfold without collaborative efforts and policies. The commitment of various individual countries, as well as companies, will undoubtedly affect emission sources. Major conclusions from the study included-

1. CFC emission is likely to be considerably lower from the previous estimate, especially if all the countries abide by the London Amendment to the Montreal protocol.
2. The OCED members' compliance to achieve and stabilise CO2 emissions might have a significant impact on their emissions but a smaller impact on global emissions by 2100.
3. Population and economic growth, availability of fossil fuels at low cost and increased deforestation rate gravitate more greenhouse gases. Whereas, availability of renewable energy supply, plantation of biomass, restriction on conventional air pollution and improvement in agricultural productivity decreases greenhouse emission.
4. IS92a&b scenarios fall within the short-term scenarios previously reported by the World Energy Council and International Energy Council.
5. There remains a need to calculate sector-wise greenhouse emission as well as hidden human-induced emissions.