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What do the emissions scenarios mean?

The amount of greenhouse gas emissions that are emitted into the atmosphere over the next few decades could follow a number of different pathways, depending on global mitigation efforts. The emissions scenarios provided in UKCP09 give three possible future pathways for emissions that do not include planned mitigation measures, though they do include technological and economic change that has an impact on levels of emissions. If the world is successful at mitigating climate to maintain global temperatures below 2ºC, it is likely that none of the emissions scenarios used in UKCP09 will be realised. However, it is prudent to plan adaptation strategies that are robust across a range of future climates.

In detail

Modelling of future climate change requires estimation of future levels of greenhouse gas emissions. Future greenhouse gas emissions are the product of very complex dynamic systems, determined by factors such as population change, socio-economic development, and technological advances.

The importance of emissions scenarios on future climate becomes increasingly significant beyond the middle of the century.

In 2000, the Intergovernmental Panel on Climate Change (IPCC) in their Special Report on Emissions Scenarios (SRES) developed a series of 40 greenhouse gas and aerosol emissions scenarios. Each of the individual SRES scenarios represents a variation within one of four main storylines, labelled A1, A2, B1 and B2. They are commonly depicted on two axes. The horizontal axis represents the system of governance ranging from autonomy, where power remains at the regional/national level, to interdependence, where power increasingly moves to other institutions, for example, the European Union. The vertical axis shows social values, ranging from individualistic values to community-oriented values. 		  You may also be
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SRES illustrated

 

Each storyline was developed based on different assumptions about how the world will change between now and 2100.

The A1 storyline assumes that:

  • Global population peaks at almost 9 billion in 2050 before falling to around 7 billion by 2100.

  • The global economy grows during the 21st century at a similar rate (2.9% per year) as experienced during the 20th century (2.7% per year). Some reductions in income inequalities are achieved as a by-product of economic growth.

  • Total global energy use continues to grow and is around six times greater in 2100 than in 1990.

  • Under the A1FI (fossil intensive) scenario, the current dominance of fossil fuels is maintained through the 21st century. The proportion of energy generated from coal increases from 24% in 1990 to over 30% by 2050. There is little change in the proportion of energy generated from nuclear and renewable sources until 2050.

The A2 storyline assumes that:

  • Global population exceeds 15 billion by 2100, almost three times larger than in 1990.

  • The global economy grows at a slower rate than in other SRES storylines, but the average growth rate between 1990 and 2100 of 1.3% per year is higher than that observed between 1970 and 1995.

  • Total global energy use continues to grow and is almost five times greater in 2100 than in 1990.

  • There is a marked increase in the proportion of energy generated from coal, rising from 24% in 1990 to over 50% by 2100. There is a corresponding decrease in the share of energy generated from oil, declining from 43% in 1990 towards zero by 2100. Nuclear and renewable energy sources gradually increase in importance from 1990 to 2100.

The B1 storyline assumes that:

  • Global population peaks at almost 9 billion in 2050 before falling to around 7 billion by 2100.

  • The global economy grows during the 21st century at a rate of 2.5% per year, which is slightly less than during the 20th century. Income inequalities are reduced as a direct result of constant domestic and international efforts.

  • As a result of energy intensity improvements, total global energy use grows at a slower rate that in other SRES storylines, peaking in 2050 at just over double the 1990 total. Between 2050 and 2100, total global energy use falls significantly and is returning towards the 1990 total.

  • There is a major shift in energy production towards nuclear and renewable sources. Until 2050, the global energy system remains fossil fuel dominated, but with a move away from coal and towards natural gas. By 2100, the transition away from fossil fuels is well underway, with nuclear and renewable energy accounting for 53% of total global energy (up from 18% in 1990).

The B2 storyline assumes that:

  • Global population increases to about 9.4 billion by 2050 and about 10.4 billion by 2100, in line with recent median global population projections.

  • The global economy grows at 2.2% per year, slower than the long-term historical average, and income inequalities remain higher than those in the A1 or B1 storylines.

  • Energy intensity improvements are slower than in the A1 or B1 storylines, and by 2100 total global energy use reaches almost four times the 1990 total.

  • A trend towards increased use of natural gas, followed by nuclear and renewable energy and finally – as oil and gas start to become scarce – an increasing return to coal. This means that by 2100 there is a broad mixture of different energy sources, with nuclear and renewable energy producing 49% of energy (up from 18% in 2100).

Based on the current understanding, the emission scenarios that have been used in UKCP09 are:

  • High – A1FI
  • Medium – A1B
  • Low – B1

Find out more


  • BESEECH – Building Economic and Social information for Examining the Effects of Climate cHange
Last Updated Wednesday, 15 December 2010