365 Days of Climate Awareness 323 –Boundary Conditions: Emissions Scenarios

Boundary conditions are mathematical expressions of the limits and inputs of a system. The many and complicated sets of equations—enough to fill 18,000 printed pages--which compose general circulation models (GCMs) require these boundary conditions to even run. Without them, there isn’t enough information for a computer to obtain results. And if these boundary conditions are unrealistic, the model will go off the rails and give wildly bad results. These boundary conditions tend to be empirical, that is, based on observations. However, a number are themselves derived from models, making them semi-empirical. But for climate modeling, foremost among the boundary conditions are emissions scenarios.

There are several very important sets of boundary conditions. These include:

•           Topography (treated as constant)
•            Ocean bathymetry (treated as constant)
•            Incoming solar radiation (varies with time)
•           Land-use scenarios (change over time)
•           Emissions scenarios (change over time)

IPCC Carbon pathways.

The last two themselves are the results of two sets of complex projections. One is called “Shared Socioeconomic Pathways” (SSPs). These pathways represent varying levels of international cooperation and technological progress:

•         Population trends
•          Economic activity
•          Technological development
•          Political and social will for change

The five SSPs are:

• .      SSP1: sustainable pathway. Global commons ar preserved, limits of nature are respected.
• .      SSP2: medium pathway. Limited cooperation between states. Global population growth is moderate and environmental systems degrade.
• .      SSP3: Regional rivalry. Nationalism and regional conflicts push global issues into the background.
• .      SSP4: Inequality. Contrast between globally cooperating societies and those stalling is widening. Environmental policies address local problems in some regions, but not in others.
• .      SSP5: Fossil-fueled Development. Innovations, technological progress and an energy-intensive lifestyle worldwide based on increased use of fossil fuels.

The second set of projections are called “Representative Carbon Pathways” (RCPs), and these represent different climatic scenarios with various levels of radiative forcings (global heat gain, post #91). They are stated as temperature gains over 1750 average, and range from 1.9°C/3.4°F to 8.5°C/15.3°F. Treating these two broad topics—socioeconomic factors and environmental impacts—separately produced a wide range of possible global warming scenarios. In the climate models, both SSPs and RCPs are boundary conditions which help determine the state of the world climate by 2100.

Tomorrow: West Virginia v. the EPA.

Be brave, be steadfast, and be well.