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Safe landing approach
See tolerable windows approach.

Scenario
A plausible and often simplified description of how the future may develop, based on a coherent and internally consistent set of assumptions about key driving forces (e.g., rate of technology change, prices) and relationships. Note that scenarios are neither predictions nor forecasts.

Sequestration
The process of increasing the carbon content of a carbon reservoir other than the atmosphere. Biological approaches to sequestration include direct removal of carbon dioxide from the atmosphere through land-use change, afforestation, reforestation, and practices that enhance soil carbon in agriculture. Physical approaches include separation and disposal of carbon dioxide from flue gases or from processing fossil fuels to produce hydrogen- (H₂) and carbon dioxide-rich fractions and long-term storage underground in depleted oil and gas reservoirs, coal seams, and saline aquifers.

SF₆
See sulphur hexafluoride.

Sinks
Any process or activity or mechanism that removes a greenhouse gas, an aerosol, or a precursor of a greenhouse gas or aerosol from the atmosphere.

Social costs
The social cost of an activity includes the value of all the resources used in its provision. Some of these are priced and others are not. Non-priced resources are referred to as externalities. It is the sum of the costs of these externalities and the priced resources that makes up the social cost. See also private cost, external cost, and total cost.

Socio-economic potential
The socio-economic potential represents the level of GHG mitigation that would be approached by overcoming social and cultural obstacles to the use of technologies that are cost-effective. See also economic potential, market potential, and technology potential.

Source
A source is any process, activity or mechanism that releases a greenhouse gas, an aerosol, or a precursor of a greenhouse gas or aerosol into the atmosphere.

Spillover effect
The economic effects of domestic or sectoral mitigation measures on other countries or sectors. In this report, no assessment is made on environmental spillover effects. Spillover effects can be positive or negative and include effects on trade, carbon leakage, transfer, and diffusion of environmentally sound technology and other issues.

Stabilization
The achievement of stabilization of atmospheric concentrations of one or more greenhouse gases (e.g., carbon dioxide or a CO₂-equivalent basket of greenhouse gases).

Stabilization analysis
In this report this refers to analyses or scenarios that address the stabilization of the concentration of greenhouse gases.

Stabilization scenarios
See stabilization analysis.

Stakeholders
Person or entity holding grants, concessions, or any other type of value or interest that would be affected by a particular action or policy.

Standards
Set of rules or codes mandating or defining product performance (e.g., grades, dimensions, characteristics, test methods, and rules for use). International product and/or technology or performance standards establish minimum requirements for affected products and/or technologies in countries where they are adopted. The standards reduce greenhouse gas emissions associated with the manufacture or use of the products and/or application of the technology. See also emissions standards, regulatory measures.

Stock
See reservoir.

Storyline
A narrative description of a scenario (or a family of scenarios) that highlights the main scenario characteristics, relationships between key driving forces, and the dynamics of the scenarios.

Structural change
Changes, for example, in the relative share of Gross Domestic Product produced by the industrial, agricultural, or services sectors of an economy; or more generally, systems transformations whereby some components are either replaced or potentially substituted by other ones.

Subsidy
Direct payment from the government to an entity, or a tax reduction to that entity, for implementing a practice the government wishes to encourage. Greenhouse gas emissions can be reduced by lowering existing subsidies that have the effect of raising emissions, such as subsidies to fossil fuel use, or by providing subsidies for practices that reduce emissions or enhance sinks (e.g., for insulation of buildings or planting trees).

Sulphur hexafluoride (SF₆)
One of the six greenhouse gases to be curbed under the Kyoto Protocol. It is largely used in heavy industry to insulate high-voltage equipment and to assist in the manufacturing of cable-cooling systems. Its Global Warming Potential is 23,900.

Supplementarity
The Kyoto Protocol states that emissions trading and Joint Implementation activities are to be supplemental to domestic actions (e.g., energy taxes, fuel efficiency standards, etc.) taken by developed countries to reduce their greenhouse gas emissions. Under some proposed definitions of supplementarity (e.g., a concrete ceiling on level of use), developed countries could be restricted in their use of the Kyoto mechanisms to achieve their reduction targets. This is a subject for further negotiation and clarification by the parties.

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