Modeling for Sustainability

Human-caused climate change is becoming more apparent with each year.  Our Industrial civilization is at a crossroads.  For over 200 years, the industrialized world has been increasingly dependent on fossil fuels – coal, oil, natural gas - to grow food, make things, travel, and heat and cool our buildings.  However, the carbon dioxide generated by burning fossil fuels, along with other human introduced gases, is destabilizing the Earth’s climate, with far-reaching consequences now and well into the future. 

Climate change is a direct result of greenhouse gases (GHGs) we have introduced to the atmosphere.  GHGs are the gaseous compounds that can absorb and trap the radiant heat that the Earth's surface normally emits back into space.  The Earth must emit part of the Sun’s warmth back into space in order to keep the planet from overheating – and to keep the climate stable.

Nitrogen and oxygen, the two compounds that make up the vast majority of the atmosphere, are not greenhouse gases and do not trap the Earth’s heat.  This is because they are “diatomic” molecules, made of two atoms (N2 and O2).  As a result, they do not possess certain physical attributes that allow them to absorb radiant heat. However, most gases that are made up of three or more atoms – such as carbon dioxide (CO2), methane (CH4), water vapor (H2O) and many synthetic (man-made) gases, are GHGs.  Often, the more atoms a gaseous molecule has, the more potent it is as a GHG.

Aside from water vapor, most GHGs are in trace amounts in the atmosphere.  The second most prevalent GHG (after water vapor), carbon dioxide, is at 400+ parts per million, only about one molecule in 2,500 in the air.  Yet it can exert an enormous influence on climate.  Other synthetic gases, such as refrigerants, which leak out of refrigerators and air conditioners, compound the GHG problem. 


Carbon dioxide is naturally removed from the atmosphere through the process of plant photosynthesis, where it becomes the carbon backbone of plant matter.  We can encourage this carbon dioxide removal through specific land use practices, such as reforestation or afforestation (establishing trees where none existed previously).  If we then ensure the captured plant carbon remains in the soil long-term, we employ the practice called Carbon Sequestration (Sequestration for short).  This is currently our only cost-effective means for removing atmospheric carbon dioxide.

Much work has been done in recent years to measure the steadily increasing concentration of GHGs added to the atmosphere, and understand where they are coming from.  The state of California maintains a statewide inventory of “direct” GHG emissions sources – those that come from the tailpipes, chimneys, and smokestacks located in the state.

A local nonprofit, The Climate Center, is promoting policies to support the rapid reduction of GHG emissions within California, with the goal of achieving net zero GHG emissions by 2030, through a combination of rapid reductions of existing sources, coupled with aggressive sequestration practices on “working lands” (such as croplands and pasture).

When they wanted to know effective these policies would be in reducing GHG emissions, they requested ECMC develop a mathematical model to estimate the GHG emissions impact, compared to the degree of adoption of the steps over the next ten years.

The model, called Climate Safe Pathways, was developed as a Microsoft Excel workbook, consisting of several workbooks: computational, charting, and documentation.  It is based on California’s statewide GHG inventory, and other available data provided by the scientific and policy making community.  It includes a model developed by another firm, Carbon Cycle Institute, to quantify the amount of sequestration available in California to offset hard to eliminate emissions, with the goal of net zero emissions (sequestration equal to emissions).

The overall Pathways concept is to quantify the tangible actions as specific indices, (which are inputs to the Pathways model) and estimate the impact of each on statewide GHG emissions.  These indices are intended to be adjusted by users, allowing them to view the estimated impact on the resulting GHG emissions, through changes in the model values, and on summary bar charts.  The hope is it will promote a deeper understanding of the challenges we face in the years ahead, as we address the climate change issue.

The Pathways model is available for download on The Climate Center’s website here: