Sustainability refers to systems and not individual components of systems. Individual species are often set apart to represent resource sustainability, which creates grave misconceptions of available harvest. Much like the myriad of elements necessary for human survival, all species are supported by systems. If the systems are capable of adapting to changing conditions or stress, they can be considered sustainable. Intense targeting of one species for harvest impacts a resource system, even if we don’t think it does.
Scientists are growing more concerned about sustainability, not so much because of change itself but because of the rate change some systems are trying to accommodate.
Once a resource system has been internally or externally stressed beyond its ability to successfully adapt, The “tipping point will have been exceeded. The integrity of the system will vanish as energy spills from the system into a new form. While resource systems are not really considered linear, some of their responses under stress can be modeled as linear. However, once a system collapses, the linearity will unpredictably translate into a new, lateral form which cannot be modeled ahead of time.
Tipping points usually can’t be modeled because if we understood the system that well we would be able to manage it better. It is a widespread misconception that if we simply remove a stress, the system will regain sustainability. (See Sustainability: Case Studies, Case Study # 2. Without intervention, would this system have regained sustainability simply by removing anthropogenic stress? Possibly but over what time period and what would the resource look like by then?)
Resource system interventions are well meant but often result in only delaying system collapse. Once a system accrues stress, it takes much less additional stress to reach a tipping point. The additional stress could be anthropogenic or part of the natural system stress which a healthy system could have adapted to.
In addition to their own system, individual species need external links to other systems to survive. In this MA DEP Stream Crossing booklet photo, a salmon struggles to reach its breeding grounds so the species can survive. The breeding stream is one example of a system which is externally linked to the salmon’s survival. The stream overflowed its banks, blocking the existing culvert with branches and debris and the water flooded the road. Perhaps the culvert was undersized to begin with or perhaps it is undersized now due to increased precipitation from climate change. Behind this fish, are more fish. They may become a lost year class for the species.
Tipping points may also be relevant for ocean currents. The graph below represents various climate change models for predicted changes in part of the North Atlantic Drift Current, which delivers significant heat to Western Europe. For a number of linked reasons, this current has been reduced. While the models represent somewhat linear behavior, the results of that behavior have no way of being modeled. Also, in this case the contributions of the Gulf Stream, which is a wind driven current, have not been considered in the reduced current flow.
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This satellite thermal image shows a critical juncture between two significant ocean currents, just south of Cape Cod. The bright colors of the warm Gulf Stream on the lower part and the dark colors of the cold Labrador current on the top. The green color marks a mixing eddy current between the two systems. Where the Labrador current actually meets the Gulf Stream determines where the north wall of the Stream will be, how close to shore the Stream flows and when it will turn east for Europe. There have been studies indicating a possible slow down in the transport volume of the Labrador current, which may or may not be linked to predicted slow downs in other ocean currents.Ocean currents may have linkages which support each other as sustainable systems and they may have tipping points.
This is an image of how the two currents interact along the coast.
