← Environmental Science syllabus

United StatesEnvironmental Science

Unit 9: Global Change

10 dot points across 10 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What pushes a species toward extinction, and how do we pull it back?

Topic 9.9 Endangered Species: explain the factors that make species vulnerable to extinction and describe how endangered species are protected.
A focused answer to APES Topic 9.9, covering what makes a species endangered, the traits that increase extinction risk, the human causes, conservation strategies (protected areas, captive breeding, the Endangered Species Act, CITES), and keystone species, with a worked minimum-viable-population example.
9 min answer →

What changes as the planet warms, and how do feedback loops make it worse?

Topic 9.5 Global Climate Change: describe the evidence and effects of global climate change and explain the role of positive feedback loops.
A focused answer to APES Topic 9.5, covering the evidence for global climate change, its effects (rising temperatures, melting ice, sea-level rise, extreme weather, shifting species), positive feedback loops (ice-albedo, permafrost methane, water vapor), the difference between weather and climate, and mitigation and adaptation, with a worked sea-level reasoning example.
10 min answer →

What are the big human pressures driving species loss, and why does losing biodiversity matter?

Topic 9.10 Human Impacts on Biodiversity: identify the major human causes of biodiversity loss (HIPPCO) and explain why declining biodiversity matters.
A focused answer to APES Topic 9.10, covering the HIPPCO causes of biodiversity loss, why habitat loss is the largest, the importance of biodiversity for ecosystem services and resilience, the sixth mass extinction, and conservation responses, with a worked species-loss reasoning example.
10 min answer →

Why are greenhouse gases rising, and which human activities are to blame?

Topic 9.4 Increases in the Greenhouse Gases: identify the human activities that increase greenhouse gases and explain why their concentrations are rising.
A focused answer to APES Topic 9.4, covering the human activities that raise greenhouse gases (fossil fuel combustion, deforestation, agriculture, landfills, industry), the specific sources of carbon dioxide, methane and nitrous oxide, the role of the carbon cycle, and the Keeling Curve evidence, with a worked emissions calculation.
9 min answer →

Why can a species that is harmless at home wreck an ecosystem somewhere new?

Topic 9.8 Invasive Species: explain what makes a species invasive and describe the impacts of invasive species and how they are managed.
A focused answer to APES Topic 9.8, covering what makes a species invasive, how they are introduced, why the lack of natural predators lets them spread, their impacts on native species and ecosystems, the link to climate change, and methods of control, with a worked exponential-spread reasoning example.
9 min answer →

How does carbon dioxide make the sea more acidic, and why does that dissolve shells?

Topic 9.7 Ocean Acidification: explain how rising carbon dioxide acidifies the ocean and describe the effects on marine organisms.
A focused answer to APES Topic 9.7, covering how the ocean absorbs carbon dioxide to form carbonic acid, the resulting fall in pH, why acidification harms shell- and skeleton-building organisms (corals, shellfish, plankton), the effect on carbonate availability, the link to food webs, and how it differs from ocean warming, with a worked pH and carbonate reasoning example.
9 min answer →

What does a warmer ocean do to coral, sea level and marine life?

Topic 9.6 Ocean Warming: explain how the ocean absorbs heat and describe the effects of ocean warming on marine ecosystems and sea level.
A focused answer to APES Topic 9.6, covering how the ocean absorbs most of the extra heat from climate change, coral bleaching, thermal expansion and sea-level rise, shifting species ranges, reduced oxygen, effects on currents, and why the ocean buffers but does not escape warming, with a worked thermal-expansion reasoning example.
9 min answer →

How did the world manage to start healing the ozone layer?

Topic 9.2 Reducing Ozone Depletion: describe the strategies and international agreements used to reduce ozone depletion and how the ozone layer is recovering.
A focused answer to APES Topic 9.2, covering the Montreal Protocol, the phase-out of CFCs, substitutes (HCFCs and HFCs) and their trade-offs, why ozone recovery is slow, the success of international cooperation, and the lesson for other global problems, with a worked recovery-timescale reasoning example.
9 min answer →

What punched a hole in the ozone layer, and why does it matter?

Topic 9.1 Stratospheric Ozone Depletion: explain how CFCs deplete stratospheric ozone and describe the consequences of a thinner ozone layer.
A focused answer to APES Topic 9.1, covering the protective role of stratospheric ozone, how CFCs release chlorine that catalytically destroys ozone, the Antarctic ozone hole, the consequences of increased UV (skin cancer, cataracts, harm to ecosystems), and the difference from ground-level ozone, with a worked catalytic-destruction reasoning example.
10 min answer →

How do gases in the air keep the planet warm, and which gases matter most?

Topic 9.3 The Greenhouse Effect: explain the greenhouse effect, identify the major greenhouse gases, and distinguish the natural effect from the enhanced effect.
A focused answer to APES Topic 9.3, covering how the greenhouse effect works, the major greenhouse gases (carbon dioxide, methane, nitrous oxide, water vapor, CFCs), the difference between the natural and enhanced greenhouse effect, global warming potential and residence time, with a worked global warming potential calculation.
10 min answer →