Emission scenario

Emission scenarios are possible pathways that society might take in the the emission of greenhouse gases in the future. It is hard to predict what will occur in society in the next 5 years, let alone to predict the next 100. Society could continue to pollute heavily, or it could switch to minimal emissions in harnessing its energy, or anything in between.

By making assumptions on how society will develop, such as how the world population will grow and how world economies interact, it is possible to estimate the world's future emissions and their effects on the climate. This is known as the Storyline Approach.

Another method is to simply assume emissions at some point in the future, and then see what steps society might need to take to get there. This approach is known as the Representative Concentration Pathways (RCP), and will be discussed alongside the Storyline Approach.

What determines different emission scenarios?

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The determining factors for emission scenarios are known as driving forces. The main forces that "drive" society's future emissions are:[1]

  • Population growth
  • Energy use changes
  • Economic development
  • Technological development and
  • Land use change

Each of the driving forces affect how society emits pollutants, specifically greenhouse gases. If the population grows drastically, GHG emissions are expected to increase with it. If technology develops such that electrical generation becomes more efficient, then GHG emissions may be able to decrease. There are many combinations of these driving forces that can occur, thus leading to various scenarios.

Visit driving forces for emission scenarios for more information.

Emission scenarios

Below is a summary of the two emission scenario methods taken by the IPCC in past reports. The video at the bottom of the page discusses each in more detail, along with images and results from the different approaches. Effects of the scenarios on the climate are discussed here.

Storyline Approach

The scenarios developed by the IPCC in the Special Report on Emissions Scenarios (SRES) are a result of four different storylines, titled A1, A2, B1, and B2. Each storyline assumes a distinctly different direction for future developments of driving forces. From these assumptions, each storyline differs in increasingly irreversible ways resulting in drastically different end scenarios.[1]

The four scenarios are as follows:

  1. A1 (Global/Economic) - This storyline describes a future world of rapid economic growth, with a global population that peaks in the mid 2000's and declines afterwards. The A1 storyline is also split into 3 further groups: A1FI follows a "business as usual" fossil fuel intensive future, A1B is a balanced energy picture, and A1T is a non-fossil fuel future.
  2. A2 (Local/Economic) - The A2 storyline follows a more conservative economic world, where economic growth is more limited to smaller regions of the world. Technological change is slower in this storyline, while high fertility rates result in a booming population.
  3. B1 (Global/Environmental) - The B1 storyline assumes the same population growth as the A1 storyline. It differs in that it has less of a material intense society, and focuses more on clean and efficient technologies. It takes emphasis on global solutions to economic, social and environmental sustainability, but with no additional climate incentives.
  4. B2 (Local/Environmental) - The B2 storyline focuses on a society that looks for local solutions to economic, social, and environmental sustainability. It is a world with continuously increasing global population in accordance with the UN prediction, with intermediate levels of economic development, and less rapid technological change compared to the B1 and A1 storylines. It focuses on local and regional solutions to environmental protection and social equity.

Representative Concentration Pathways

Representative Concentration Pathways were adopted in the IPCC's 5th assessment report. As mentioned before, RCPs assume end points of emissions giving a clear pathway for emissions to take in the future. How these endpoints are reached is another story, and could depend on a wide variety of driving force combinations. The year that is defined up to is 2100, chosen to give a wide range of possible outcomes.[2]

Four pathways are set, defined by endpoint values for radiative forcing by the year 2100. The lowest emission scenario peaks in emissions by 2050, declining afterwards, therefore called RCP3PD (Peak/Decline). The highest emission scenario on the other hand is called RCP8.5, as it reaches 8.5 W/m2 by the year 2100.[2]

In the video below Professor of Instruction Dr. Harris[3] explains the scenarios resulting from these storylines and representative concentration pathways. Implications of each are discussed along with them, giving a nice summary of the two methods.


  1. 1.0 1.1 IPCC. (Accessed May 9, 2016). "IPCC Special Report on Emissions Scenarios" [Online], Available: https://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf
  2. 2.0 2.1 IPCC. (Accessed June 1, 2016). Representative Concentration Pathways (RCPs) [Online], Available: http://sedac.ipcc-data.org/ddc/ar5_scenario_process/RCPs.html
  3. This video is used with the gracious permission of Dr. S. Harris in a private communication with Jason Donev on 2016-6-12.