Working Group III: Mitigation

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Targets and timetables
A target is the reduction of a specific percentage of greenhouse gas emissions from a baseline date (e.g., “below 1990 levels”) to be achieved by a set date, or timetable (e.g., 2008 to 2012). For example, under the Kyoto Protocol’s formula, the European Union has agreed to reduce its greenhouse gas emissions by 8% below 1990 levels by the 2008 to 2012 commitment period. These targets and timetables are, in effect, an emissions cap on the total amount of greenhouse gas emissions that can be emitted by a country or region in a given time period. See also quantified emission limitation or reduction commitments.

Tax-interaction effect
See interaction effect.

Technological potential
The amount by which it is possible to reduce greenhouse gas emissions or improve energy efficiency by implementing a technology or practice that has already been demonstrated. See also economic potential, market potential, and socio-economic potential.

A piece of equipment or a technique for performing a particular activity.

Technology or performance standard
See standard.

Technology transfer
The broad set of processes that cover the exchange of knowledge, money, and goods among different stakeholders that lead to the spreading of technology for adapting to or mitigating climate change. As a generic concept, the term is used to encompass both diffusion of technologies and technological co-operation across and within countries.

Tolerable windows approach
These approaches analyse greenhouse gas emissions as they would be constrained by adopting a long-term climate - rather than greenhouse gas concentration stabilization - target (e.g., expressed in terms of temperature or sea level changes or the rate of such changes). The main objective of these approaches is to evaluate the implications of such long-term targets for short- or medium-term “tolerable” ranges of global greenhouse gas emissions. Also referred to as safe landing approaches.

Top-down models
The terms “top-down” and “bottom-up” are shorthand for aggregate and disaggregated models. The top-down label derives from how modellers applied macroeconomic theory and econometric techniques to historical data on consumption, prices, incomes, and factor costs to model final demand for goods and services, and supply from main sectors, like the energy sector, transportation, agriculture, and industry. Therefore, top-down models evaluate the system from aggregate economic variables, as compared to bottom-up models that consider technological options or project specific climate change mitigation policies. Some technology data were, however, integrated into top-down analysis and so the distinction is not that clear-cut.

Total cost
All items of cost added together. The total cost to society is made up of both the external cost and the private cost, which together are defined as social cost.

Trace gas
A minor constituent of the atmosphere. The most important trace gases that contribute to the greenhouse effect are, inter alia, carbon dioxide, ozone, methane, nitrous oxide, perfluorocarbons, chlorofluorocarbons, hydrofluorocarbons, sulphur hexafluoride, methyl chloride, and water vapour.

Tradable quota system
See emissions trading.

Trade effects
Economic impacts of changes in the purchasing power of a bundle of exported goods of a country for bundles of goods imported from its trade partners. Climate policies change the relative production costs and may change terms of trade substantially enough to change the ultimate economic balance.

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