The twelve leverage points to intervene in a system were proposed by Donella Meadows, a scientist and system analyst who studied environmental limits to economic growth.
History The leverage points, first published in 1997, were inspired by Meadows' attendance at a North American Free Trade Agreement (NAFTA) meeting in the early 1990s, where she realized a very large new system was being proposed but the mechanisms to manage it were ineffective. Meadows, who worked in the field of systems analysis, proposed a scale of places to intervene in a system. Awareness and manipulation of these levers is an aspect of self-organization and can lead to collective intelligence. Her observations are often cited in energy economics, green economics and human development theory. Meadows started with the observation that there are levers, or places within a complex system (such as a firm, a city, an economy, a living being, an ecosystem, an ecoregion) where a "small shift in one thing can produce big changes in everything" (compare: constraint in the sense of the theory of constraints). She claimed we need to know about these shifts, where they are, and how to use them. She said most people know where these points are instinctively, but tend to adjust them in the wrong direction. A greater understanding would help solve global problems such as unemployment, hunger, economic stagnation, pollution, resources depletion, and conservation issues. Meadows started with a nine-point list of such places, and expanded it to a list of twelve leverage points with explanations and examples, for systems in general. She describes a system as being in a certain state, consisting of a stock and flow, with inflows (amounts entering the system) and outflows (amounts leaving the system). At a given time, the system is in a certain perceived state. There may also be a goal for the system to be in a certain state. The difference between the current state and the goal is the discrepancy.
For example, one might consider a lake or reservoir, which contains a certain amount of water. The inflows are the amount of water coming from rivers, rainfall, drainage from nearby soils, and waste water from a local industrial plant. The outflows might be the amount of water used up for irrigation of nearby cornfield, water taken by that local plant to operate as well as the local camping site, water evaporating in the atmosphere, and trickling surplus water when the reservoir is full. Local inhabitants complain about the water level getting low, pollution getting higher, and the potential effect of hot water release in the lake on life (in particular, the fish). This is the difference between the perceived state (pollution or low water level) and the goal (a non-polluted lake).
Leverage points to intervene in a system The following are in increasing order of effectiveness.
12. Constants, parameters, numbers Parameters are points of lowest leverage effects. Though they are the most clearly perceived among all leverages, they rarely change behaviors and therefore have little long-term effect. For example, climate parameters may not be changed easily (the amount of rain, the evapotranspiration rate, the temperature of the water), but they are the ones people think of first (they remember that in their youth, it was certainly raining more). These parameters are indeed very important. But even if changed (improvement of upper river stream to canalize incoming water), they will not change behavior much (the debit will probably not dramatically decrease).
11. The size of buffers and other stabilizing stocks, relative to their flows A buffer's ability to stabilize a system is important when the stock amount is much higher than the potential amount of inflows or outflows. In the lake, the water is the buffer: if there's a lot more of it than inflow/outflow, the system stays stable. For example, the inhabitants are worried the lake fish might die as a consequence of hot water release directly in the lake without any previous cooling off. However, the water in the lake has a large heat capacity, so it's a strong thermic buffer. Provided the release is done at low enough depth, under the thermocline, and the lake volume is big enough, the buffering capacity of the water might prevent any extinction from excess temperature. Buffers can improve a system, but they are often physical entities whose size is critical and can't be changed easily.
10. Structure of material stocks and flows (such as transport network, population age structures) A system's structure may have enormous effect on operations, but may be difficult or prohibitively expensive to change. Fluctuations, limitations, and bottlenecks may be easier to address. For example, the inhabitants are worried about their lake getting polluted, as the industry releases chemical pollutants directly in the water without any previous treatment. The system might need the used water to be diverted to a wastewater treatment plant, but this requires rebuilding the underground used water system (which could be quite expensive).
9. Length of delays, relative to the rate of system changes Information received too quickly or too late can cause over- or underreaction, even oscillations. For example, the city council is considering building the wastewater treatment plant. However, the plant will take 5 years to be built, and will last about 30 years. The first delay will prevent the water being cleaned up within the first 5 years, while the second delay will make it impossible to build a plant with exactly the right capacity.
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