Understanding Climate Models


The Emission Scenarios of the IPCC Special Report on Emission Scenarios (SRES)

A1. The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil-intensive (A1FI), non-fossil energy sources (A1T) or a balance across all sources (A1B) (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end use technologies).

A2. The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self-reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily regionally oriented and per capita economic growth and technological change more fragmented and slower than other storylines.

B1. The B1 storyline and scenario family describes a convergent world with the same global population, that peaks in mid-century and declines thereafter, as in the A1 storyline, but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.

B2. The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to economic, social and environmental sustainability. It is a world with continuously increasing global population, at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented towards environmental protection and social equity, it focuses on local and regional levels.

An illustrative scenario was chosen for each of the six scenario groups A1B, A1FI, A1T, A2, B1 and B2. All should be considered equally sound.

The SRES scenarios do not include additional climate initiatives, which means that no scenarios are included that explicitly assume implementation of the United Nations Framework Convention on Climate Change or the emissions targets of the Kyoto Protocol.


Source: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-projections-of.html



Projected global average surface warming and sea level rise at the end of the 21st century. {10.510.6Table 10.7}



Temperature Change 

Sea Level Rise) 

(°C at 2090-2099 relative to 1980-1999)a 

(m at 2090-2099 relative to 1980-1999) 


Best estimate  

Likely range  

Model-based range excluding future 

rapid dynamical changes in ice flow 

Constant Year 2000 concentrations 


0.3 – 0.9  


B1 scenario  


1.1 – 2.9  

0.18 – 0.38 

A1T scenario  


1.4 – 3.8  

0.20 – 0.45 

B2 scenario  


1.4 – 3.8  

0.20 – 0.43 

A1B scenario  


1.7 – 4.4  

0.21 – 0.48 

A2 scenario  


2.0 – 5.4  

0.23 – 0.51 

A1FI scenario  


2.4 – 6.4  

0.26 – 0.59 

Table notes:

a These estimates are assessed from a hierarchy of models that encompass a simple climate model, several Earth System Models of Intermediate Complexity and a large number of Atmosphere-Ocean General Circulation Models (AOGCMs).

b Year 2000 constant composition is derived from AOGCMs only.

Source: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-projections-of.html


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