The model represents the world in terms of three state variables (stocks): population, environmental pollution, and production capacity (all standardized to an initial value of 1).
The global human population increases by births and is reduced by deaths. The number of births per year depends on the size of the population, the birth rate, and a birth control parameter. It is also affected by the consumption level and by the quality of environment.
Environmental pollution arises from the interplay of environmental degradation and regeneration. The amount of degradation depends on population, its consumption level and the specific degradation rate. Regeneration is determined by a damage threshold, the quality of environment and current environmental pollution.
Production capacity increases at a rate which depends on consumption level and environmental pollution.
To see a Systo page dedicated to this model, please go here.
", "language": "system_dynamics" }, "nodes": [ { "id": "cloud1", "type": "cloud", "centrex": 37, "centrey": 239 }, { "id": "cloud2", "type": "cloud", "centrex": 352, "centrey": 243 }, { "id": "cloud3", "type": "cloud", "centrex": 265, "centrey": 113 }, { "id": "cloud4", "type": "cloud", "centrex": 628, "centrey": 117 }, { "id": "cloud5", "type": "cloud", "centrex": 614, "centrey": 341 }, { "id": "stock1", "type": "stock", "label": "Population", "centrex": 215, "centrey": 241, "equation": "1" }, { "id": "stock3", "type": "stock", "label": "Environ_pollution", "centrex": 434, "centrey": 117, "equation": "1" }, { "id": "stock5", "type": "stock", "label": "Production_capacity", "centrex": 415, "centrey": 342, "equation": "1" }, { "id": "valve1", "type": "valve", "label": "births", "centrex": 126, "centrey": 248, "equation": "birth_rate*Population*quality_of_environment*consumption_level*birth_control" }, { "id": "valve2", "type": "valve", "label": "deaths", "centrex": 283, "centrey": 342, "equation": "death_rate*Population*Environ_pollution" }, { "id": "valve3", "type": "valve", "label": "degradation", "centrex": 349, "centrey": 115, "equation": "degradation_rate*Population*consumption_level" }, { "id": "valve4", "type": "valve", "label": "regeneration", "centrex": 527, "centrey": 117, "equation": "quality_of_environment>1?regeneration_rate*Environ_pollution:regeneration_rate*damage_threshold" }, { "id": "valve5", "type": "valve", "label": "capacity_increase", "centrex": 514, "centrey": 341, "equation": "growth_rate*consumption_level*Environ_pollution*(1-(consumption_level*Environ_pollution/consumption_goal))" }, { "id": "variable1", "type": "variable", "label": "birth_rate", "centrex": 140, "centrey": 321, "equation": "0.03+rand_var(0,0.1)" }, { "id": "variable11", "type": "variable", "label": "regeneration_rate", "centrex": 643, "centrey": 170, "equation": "0.1" }, { "id": "variable13", "type": "variable", "label": "degradation_rate", "centrex": 641, "centrey": 207, "equation": "0.02" }, { "id": "variable15", "type": "variable", "label": "consumption_goal", "centrex": 630, "centrey": 250, "equation": "10" }, { "id": "variable17", "type": "variable", "label": "growth_rate", "centrex": 634, "centrey": 291, "equation": "0.05" }, { "id": "variable19", "type": "variable", "label": "consumption_level", "centrex": 469, "centrey": 233, "equation": "Production_capacity" }, { "id": "variable3", "type": "variable", "label": "birth_control", "centrex": 72, "centrey": 348, "equation": "1" }, { "id": "variable5", "type": "variable", "label": "death_rate", "centrex": 257, "centrey": 318, "equation": "0.01" }, { "id": "variable7", "type": "variable", "label": "quality_of_environment", "centrex": 318, "centrey": 50, "equation": "damage_threshold/Environ_pollution" }, { "id": "variable9", "type": "variable", "label": "damage_threshold", "centrex": 580, "centrey": 46, "equation": "1" } ], "arcs": [ { "id": "flow1", "type": "flow", "start_node_id": "cloud1", "end_node_id": "stock1", "mid_node_ids": [ "valve1" ] }, { "id": "flow2", "type": "flow", "start_node_id": "stock1", "end_node_id": "cloud2", "mid_node_ids": [ "valve2" ] }, { "id": "flow3", "type": "flow", "start_node_id": "cloud3", "end_node_id": "stock3", "mid_node_ids": [ "valve3" ] }, { "id": "flow4", "type": "flow", "start_node_id": "stock3", "end_node_id": "cloud4", "mid_node_ids": [ "valve4" ] }, { "type": "influence", "start_node_id": "variable3", "end_node_id": "valve1" }, { "type": "influence", "start_node_id": "variable9", "end_node_id": "valve4" }, { "type": "influence", "start_node_id": "variable7", "end_node_id": "valve4" }, { "type": "influence", "start_node_id": "stock3", "end_node_id": "valve4" }, { "type": "influence", "start_node_id": "variable11", "end_node_id": "valve4" }, { "type": "influence", "start_node_id": "variable13", "end_node_id": "valve3" }, { "type": "influence", "start_node_id": "variable15", "end_node_id": "valve5" }, { "id": "flow5", "type": "flow", "start_node_id": "cloud5", "end_node_id": "stock5", "mid_node_ids": [ "valve5" ] }, { "type": "influence", "start_node_id": "variable17", "end_node_id": "valve5" }, { "type": "influence", "start_node_id": "stock5", "end_node_id": "variable19" }, { "type": "influence", "start_node_id": "variable19", "end_node_id": "valve5" }, { "type": "influence", "start_node_id": "variable19", "end_node_id": "valve1" }, { "type": "influence", "start_node_id": "variable1", "end_node_id": "valve1" }, { "type": "influence", "start_node_id": "variable19", "end_node_id": "valve3" }, { "type": "influence", "start_node_id": "stock3", "end_node_id": "variable7" }, { "type": "influence", "start_node_id": "stock3", "end_node_id": "valve5" }, { "type": "influence", "start_node_id": "stock1", "end_node_id": "valve1" }, { "type": "influence", "start_node_id": "stock1", "end_node_id": "valve2" }, { "type": "influence", "start_node_id": "variable5", "end_node_id": "valve2" }, { "type": "influence", "start_node_id": "stock3", "end_node_id": "valve2" }, { "type": "influence", "start_node_id": "stock1", "end_node_id": "valve3" }, { "type": "influence", "start_node_id": "variable7", "end_node_id": "valve1" }, { "type": "influence", "start_node_id": "variable9", "end_node_id": "variable7" } ], "scenarios": { "default": { "simulation_settings": { "start_time": 0, "end_time": 50, "nstep": 20, "display_interval": 1, "integration_method": "euler1" } } } }