We consider here some examples of the use of the model to look at trajectories of change in parts of the Population, Energy Systam and Land Use sub-models, and their impact on atmospheric carbon. First, here is a graph of atmospheric carbon versus years since 1990 if all of the processes currently at play stay on their current trajectories. The blue line is the doubling of the pre-industrial revolution level of carbon in the atmosphere. The units of the y axis are billion metric tons of carbon (BMT).
Then, we used the model to simulate the atmospheric carbon under a variety of scenarios. In the first figure below, everything is the same as above, execpt the developed world reduces the carbon intensity of energy production immediately and completely in 2020. Note that the time to cross a doubling of atmospheric carbon increases by approximately 3-5 years.
In this next figure, everything is the same as in the previous figure, but the world's population stabilises in 30 years. Nothing has been done to the per capita emissions in the underdeveloped world (i.e. that continues on the current trajectory). Note the time to cross a doubling of atmospheric carbon increases by about 15 years.
In this next figure, population is again rising without control (as in the first and second figures), and the developed world is completely and abruptly decarbonised in 2020, but the carbon intensity of the underdeveloped world decreases at a rate 3% per year beginning in 2020. Note that the doubling before 2100 is almost prevented.
Also, bear in mind that none of the analyses above say anything about HOW these changes are to be made. The results simply provide estimates of what the atmospheric carbon will be IF one could find a way to change the parameters as described.