Background on En-ROADS Dynamics

As you use En-ROADS, pay attention to when and how much slider adjustments result in departures from the Baseline scenario. Ask your audience to reflect on why this happened to illuminate thinking about the dynamics of the climate and energy system that En-ROADS simulates.

Most of the dynamics in En-ROADS can be answered by these explanations:

1. Drivers of the Baseline Scenario

To gain a deeper understanding of the model’s behaviors, it is important to comprehend what factors drive the Baseline scenario.

Drivers of Growth

A challenge to limiting future warming in this simulation is the powerful growth in global GDP, which is population multiplied by GDP per person. Energy efficiency and changes to the fuel mix can help reduce energy emissions, but their success is dampened by the steady growth in GDP. Recognizing this fact leads many participants to explore different futures for population (for example, by empowering women in developing countries, which could lower population growth) and economic growth measured in GDP per person (for example, by finding ways to meet economic needs without increasing consumption).

This addresses questions such as:

  • “We’ve done a lot in energy efficiency and clean energy – why haven’t emissions reduced substantially enough?”

To illustrate this point: See the Kaya Graphs view below for a low emissions scenario with increased energy efficiency and a transition to low carbon energy sources. Even though Energy Intensity of GDP improves, and the Carbon Intensity of Energy decreases as well, Global Population and GDP per person continue to grow.


Non-CO2 Emissions Affect Temperature Significantly

Methane, N2O, and the F-gases are controlled by the Methane & Other slider. Adjusting this has a large impact on temperature. This implies significant changes in livestock management and consumption, waste management, fertilizer use, and industry. These emissions currently make up around 28% of total greenhouse gas emissions.

Addresses questions such as:

  • “We’ve done a lot in energy – why haven’t we solved the climate crisis?”

To illustrate this point: See the “Greenhouse Gas Net Emissions by Gas – Area” and “Greenhouse Gas Net Emissions” graphs and adjust the Methane & Other slider. See the scenario below – highly reducing Methane & Other emissions achieves a significant reduction in 2100 temperature.


1. Complex Interactions Between Competing Energy Supplies and Demand

Economies of Scale and Learning

Costs of energy supplies such as renewables fall as cumulative experience is gained through a learning feedback loop, also known as “economies of scale.” Every doubling of cumulative installed capacity of renewables reduces costs by around 20%, creating a reinforcing loop (this is known as the “progress ratio”). Increasing the capacity (1) and installation (2) of new energy sources leads to increased learning (3), a decrease in price (4), increasing the attractiveness of renewables (5) and therefore even greater capacity and installations:


This addresses questions such as:

  • “Why should we have hope?”

  • “How can we afford a transition to a low-carbon economy?”

  • “Aren’t the costs of renewables prohibitive?”

To illustrate this point: Look at the “Renewables Primary Energy Demand” graph in a scenario in which Renewables are subsidized. It sparks an initial exponential growth that is driven and sustained by the reinforcing learning loop figure shown above.


Delays and Capital Stock Turnover

New energy sources (e.g., renewables and new zero-carbon energy sources) take decades (not years) to scale up sufficiently to compete with coal, oil, and gas globally. One of the main sources of these delays is that new energy infrastructure is only built when old infrastructure retires or there is a need to meet increased energy demand. Only about 6% of all the world’s energy infrastructure changes each year, since infrastructure like coal-fired power plants and oil refineries can be used for 30 or more years. So while new zero-carbon energy sources may make up the majority of the market share of new energy capital, it will take many years for the old capital to turn over and be retired. The climate is only helped when coal, oil, and gas is retired away, and in the absence of other interventions, that amount is relatively small — approximately 3% per year.


This addresses questions such as:

  • “Why doesn’t subsidizing renewables, nuclear, or a new zero-carbon energy source help avoid more warming?”

This dynamic is also relevant to increasing energy efficiency, however, energy-using capital such as vehicles, buildings, and industry, has an average lifetime that is much shorter (10-15 years). One can promote increases to energy efficiency of new cars immediately, for example, but the average energy efficiency of all the cars takes decades to improve since it takes time for all the old inefficient cars to be taken off the road.

To illustrate this point: Move the New Zero-Carbon slider to huge breakthrough. Examine the “Global Sources of Primary Energy” graph and notice that, even as low-carbon sources grow, it takes several decades before enough fossil fuel capacity retires away to make much of an impact. Notice that coal, oil, and natural gas grow steadily through the 2020s and 2030s and it takes time for greenhouse gas emissions to depart from the Baseline scenario.


Implications of this dynamic: Policies that merely promote alternatives to fossil fuels take several decades to reduce carbon dioxide emissions — the existing infrastructure takes a long time to retire away. Thus, meeting climate goals also requires direct disincentives to building and using fossil fuel infrastructure.

Price and Demand Effects

Energy demand falls if energy prices rise, and demand increases if prices fall. The first dynamic is evident when carbon prices increase. The second dynamic occurs when zero-carbon energy such as renewables or a new zero-carbon energy source are either subsidized or experience a breakthrough in cost improvement.

While subsidizing low-carbon energy supplies such as Renewables, watch Final Energy Consumption increase. Inexpensive wind and solar spreading around the world decreases overall energy prices and boosts energy demand up:


On the other hand, implementing a carbon price causes energy costs to increase and consumption to decrease:


Crowding Out or Squeezing the Balloon

Many assume that if the world promoted several long term zero-carbon energy sources such as nuclear, wind, and solar, their contribution to carbon mitigation would be additive. Instead, they actually compete. More of one, less of the other.

This addresses questions such as:

  • “Why didn’t it help to have a breakthrough in a new zero-carbon energy supply in this renewable-dominated scenario?”

To illustrate this point: See the “Global Sources of Primary Energy” graph in the three scenarios below. In the first graph, we subsidize renewables alone; in the second, there is a breakthrough in a new zero-carbon energy supply; in the third graph, we see both a renewables subsidy and a new zero-carbon breakthrough.

In the following scenario, a high Renewables subsidy leads to a 0.2 degree Celsius reduction in temperature:


A huge breakthrough in New Zero-Carbon also leads to a 0.2 degree Celsius reduction on its own:


When combined, instead of seeing an additive 0.4 degree Celsius reduction, we only see a 0.3 degree reduction in temperature due to the energy supplies competing with each other for market share:


3. System Dynamics of the Climate

Bathtub Dynamics - Temperature and CO2 Concentrations Seem Weakly Responsive to CO2 Emissions

Emissions must fall significantly just to change the growth in temperature and CO2 concentrations slightly. This counterintuitive dynamic is an important feature of the carbon and climate system. A short explanation for this dynamic would include the fact that the momentum in the carbon cycle and the climate lead to long delays between emissions and temperature.

This addresses questions such as:

  • “Emissions are stabilized, so why is temperature or CO2 concentration still going up?”

To illustrate this point: See the “CO2 Emissions and Removals” and “CO2 Concentration” graphs in a scenario where CO2 emissions stabilize. Even though CO2 emissions (in red below) have flattened, CO2 concentrations (in blue on the right below) continue to increase:


Similarly, in a much more stringent scenario where CO2 concentration stabilizes, temperature change continues to increase:


To understand more about stocks, flows, and the bathtub framing below, check out our Climate Leader learning series.


Please visit for additional inquires and support.