
The IPCC climate models are highly sophisticated mathematical representations of the climate. But, for the models to predict future behavior, they must be given a set of assumed future conditions (the "what if" scenario).
In the previous report, AR4, scenarios were based on assumptions about future demographics, economics, and technology. These scenarios were described in the Special Report on Emissions Scenarios (SRES) and were called the SRES scenarios. They were called "storylines." For example, the "A1 storyline" assumed a world of very rapid economic growth, a global population that peaks in mid-century, and rapid introduction of new and more efficient technologies.
In the new report (AR5), the IPCC uses a different report to define four possible views of the future. These are called Representative Concentration Pathway (RCP) scenarios. They are defined not by assumptions based on demographics, economics and technology, but instead specify actual concentrations of greenhouse gasses and emission levels. The IPCC describes, the new scenarios "are referred to as pathways in order to emphasize that they are not definitive scenarios, but rather internally consistent sets of time-dependent forcing projections that could potentially be realized with more than one underlying socioeconomic scenario. The primary products of the RCPs are concentrations but they also provide gas emissions." (AR5, WGI, Chapter 12, Long-term Climate Change" Projections, Commitments and Irreversibility, page 1045)
Reading Assignment
Box 1.1 Description of Future Scenarios (AR5 WGI Chapter 1 Introduction)
(At first glance, this information may appear very complicated. Read slowly, be sure of acronyms, and I believe you will find it very understandable...and interesting!)
We simply do not know what climates of the future will look like. We count on climate models for this information. If we continue doing what we are doing, what will happen? If we manage ourselves differently, what will the future climate look like? Climate models are essential to our understanding and management of climate change.
Reading Assignment
From AR5 Climate Change 2013: The Physical Science Basis, Summary for Policymakers (used earlier in this lesson). Read the following section (and all subsections):D. Understanding the Climate System and its Recent Changes