5.12 Intro to Sustainability

Sustainability means using Earth's resources in a way that meets human needs now without using them up for future generations. In AP Environmental Science, you track progress toward sustainability with indicators like biodiversity, food production, global temperatures and CO2 levels, human population, and resource depletion.

Sustainability is the lens that ties Unit 5 together, so it comes back whenever you evaluate solutions to environmental problems. You will use it to weigh the benefits and drawbacks of practices like irrigation, mining, and overfishing.

Meeting Needs Without Depleting Future Resources

• Sustainability is meeting human resource needs today without depleting those resources for future generations.
• The main environmental indicators of sustainability are biological diversity, food production, average global surface temperature and CO2 concentration, human population, and resource depletion.
• Sustainable yield is the amount of a renewable resource that can be harvested without reducing the available supply.
• Sustainable yield applies to renewable resources like fish, timber, freshwater, and crops, not nonrenewable resources.
• Harvesting faster than a resource regenerates leads to depletion or collapse, which can force either species loss or a total stop in harvesting.

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Environmental Sustainability

Sustainability refers to humans living on Earth and using resources without depleting them for future generations. The goal is to balance current human needs with the long-term health of natural systems so resources are still there decades from now.

To judge whether human activity is sustainable, scientists watch a set of environmental indicators:

• Biological diversity (biodiversity): healthy ecosystems usually support a wide range of species.
• Food production: can we grow enough food without degrading the land and water that produce it?
• Average global surface temperature and CO2 concentration: rising values signal changes to climate systems.
• Human population: more people generally means more demand on resources.
• Resource depletion: how fast are we using up resources compared to how fast they replenish?

When these indicators trend in a damaging direction, it is a sign that current practices are not sustainable.

Sustainable Yield

Sustainable yield is the amount of a renewable resource that can be taken without reducing the available supply. In other words, you only harvest as much as the resource can regenerate, so the population or stock stays stable over time.

This concept applies to renewable resources such as:

• Fish populations
• Timber and forests
• Freshwater
• Crops

Determining a sustainable yield can be complex. You have to account for the resource's rate of regeneration, the demand for it, and the environmental impact of extraction. Harvesting at or below the sustainable yield keeps the resource available for future generations and helps protect the ecosystem the resource comes from.

When harvest rates exceed the rate of regeneration, the resource declines. Overfishing is a clear example: when fish are caught faster than they can reproduce, populations crash. That crash usually ends one of two ways, either the species becomes scarce or extinct, or regulations shut down harvesting to let the population recover. Both outcomes mean people lose access to the resource. Managing a fishery at its sustainable yield keeps the population steady and keeps providing that resource long term.

Explaining Sustainability and Judging Harvest Rates

Free Response:

• When a question asks you to "explain the concept of sustainability," define it as meeting current resource needs without depleting them for future generations, then tie it to specific indicators.
• If you are given data on a resource (like fish caught per year or aquifer levels), compare the harvest or use rate to the regeneration rate to argue whether the use is sustainable.
• Use sustainable yield as your reasoning when proposing or evaluating a management plan. State that harvest should not exceed what the resource can replace.

MCQ:

• Be ready to identify the environmental indicators of sustainability from a list.
• Recognize that sustainable yield applies to renewable resources, and connect a crashing population to harvest rates above the regeneration rate.

Common Trap:

• Do not treat sustainability as just "using less." It is specifically about not depleting resources so future generations still have them. Match your answer to that definition.

Common Misconceptions

• Misconception: Sustainability just means recycling or using less stuff.
  Actually: It is broader than that. It means resource use that does not deplete the resource for future generations, judged by indicators like biodiversity, food production, temperature and CO2, population, and resource depletion.
• Misconception: Sustainable yield applies to any resource.
  Actually: It applies to renewable resources that regenerate, such as fish, forests, freshwater, and crops. It does not make sense for nonrenewable resources like coal or metal ores, which do not replenish on a human timescale.
• Misconception: As long as we keep harvesting a resource, it is sustainable.
  Actually: Sustainability depends on the rate. If you harvest faster than the resource regenerates, you are depleting it, even if harvesting continues for a while before the crash.
• Misconception: Reaching sustainable yield means taking as much as possible.
  Actually: Sustainable yield is a ceiling, not a target to push past. Going over it reduces the future supply.

Related AP Environmental Science Guides

• 5.1 The Tragedy of the Commons
• 5.2 Clearcutting
• 5.0 Required Environmental Legislation
• 5.5 Irrigation Methods
• 5.4 Impacts of Agricultural Practices
• 5.3 The Green Revolution