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Frequently Asked Questions

Q1. Why use global scenarios?

A:  Global scenarios describe variations in greenhouse gas emissions.  Their output projects climate changes averaged over the entire Earth. Regional and local changes are affected by global events, and could be more intense and variable than expressed by the global net effect.  Besides, it does not matter where CO₂ is released into the atmosphere: It mixes well, so local concentrations will not vary significantly from global concentrations. For more…[link to Primer/ why global scenarios page]

Q2. What are “A2” and “B2”?

A:   Scenario A2 - assumes regional resiliency and adaptation: The underlying theme of A2 is self-reliance and preserving local identities, with economic develop being moderate and focused within regions. Compared to other plausible scenarios, global population is expected to increase at a high rate in A2. Energy consumption is high and changes in land use are moderately high. Resources are becoming scarce and technological change is fragmented and slower than in other scenarios.

Scenario B2 - assumes local resiliency and adaptation: B2 emphasizes environmental preservation and social equity with local solutions to economic, social and environmental sustainability. Global population is expected to increase continuously, yet more slowly than in scenario A2. B2 has a moderate level of economic development (like A2), but requires less energy and less change in land use than A2. Resources are more abundant and technological change is more diverse than in A2.

 

Q3. How are A2 and B2 different?

A: The A2 and B2 scenarios are not extremes. Yet they are quite different in what they anticipate the Earth might be like by the end of the 21^st century. Compared with scenario B2, scenario A2 anticipates…

• higher CO₂ concentrations
• a larger human population
• greater energy consumption
• more change in land use
• scarcer resources
• less diverse applications of technology

Q4. A2 and B2… are there more?

A: A2 and B2 are labels given to two of four families of scenarios. The A1 family, for example, is distinguished from others by its reliance on fossil fuels. A1 is split further into three groups, each depicting a different combination of fossil fuels as the major source of energy. All together, there are 40 scenarios, each considered to be equally likely, each describing a unique future scenario for the Earth. 

Q5. Is one driving force more important than the others?

A: Although we cannot know for sure, technology as a driving force of greenhouse gas emissions could be as important as population or economic development. It is important to keep in mind the large uncertainty about future changes in atmospheric composition.  Such uncertainty stems from not knowing the socio-economic conditions that drive emissions, as well as uncertainty in the biogeochemical models that relate emissions to concentrations. This uncertainty should be considered along with the errors in the climate models themselves.

Q6. Who developed the A2 and B2 scenarios, and why?

A:  IPCC developed a total of 40 emissions scenarios in its Special Report on Emissions Scenarios (SRES) for use in its Third Assessment Report (TAR).  The scenarios were designed to explore potential greenhouse gas emissions and aerosol emissions.  The ultimate purpose was to examine two questions:

-  Can institutions and agreements be put in place to manage global problems?

-  Will society focus more on material wealth than on environmental health and social well-being?

Q7. Why does CARA use the “A2” and “B2” Scenarios?

A: Not all climate modeling groups participating in the third IPCC climate assessment ran all 40 scenarios. Scenarios A2 and B2 were used the most and have received the most scientific peer review. Because their output data are widely available, these two were adopted for use in CARA.

Q8. How are climate projections made?

A: Projections of future climate are based on simulations of global climate under alterations in atmospheric composition, including changes in concentrations of greenhouse gases such as carbon dioxide (CO₂), nitrous oxide and methane, as well as sulfur concentrations.  These simulations often are called emissions scenarios.  But composition of the atmosphere also depends on what happens to the emissions.  So changes in atmospheric composition are determined from emissions scenarios in combination with biogeochemical models that predict the fate of the emitted gases. For example, a carbon cycle model is used to partition human-caused CO₂ emissions among the atmosphere, the terrestrial biosphere and the oceans.  This is because some of the CO₂ ends up staying in the atmosphere, some of it is taken up by plants, and some dissolves in ocean water.

CARA uses climate projections from Working Group 1 of the Third Assessment Report (link to http://www.grida.no/climate/ipcc_tar/index.htm) of the IPCC, derived from the IPCC Special Report on Emissions Scenarios (SRES, link to http://www.ipcc.ch/pub/sres-e.pdf). 

 

For more details, go to: Climate Change Scenarios and Projections