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.
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What this topic is asking
The College Board (Topic 9.5) wants you to describe the evidence and effects of global climate change and explain the role of positive feedback loops.
Evidence and effects
Positive feedback loops
Mitigation versus adaptation
Why this matters
Global climate change is the centerpiece of Unit 9 (its largest exam weighting) and draws together the greenhouse effect and rising gases of Topics 9.3 and 9.4 with the ocean impacts of Topics 9.6 and 9.7 and the biodiversity loss of Topic 9.10. Positive feedback loops and the mitigation-versus-adaptation distinction are among the most heavily tested ideas in the course.
Try this
Q1. Identify two pieces of evidence for global climate change. [1 point]
- Cue. Any two of rising temperature, melting ice, rising sea level, ocean warming or acidification, more extreme weather.
Q2. Explain how the ice-albedo feedback accelerates warming. [2 points]
- Cue. Warming melts reflective ice, exposing darker land or ocean that absorbs more sunlight and heat, which causes more warming and melts more ice, a self-reinforcing positive feedback.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2021 (style)4 marksSection II (FRQ). (a) Identify two pieces of evidence for global climate change. (b) Describe one effect of climate change on natural systems. (c) Explain a positive feedback loop that accelerates warming. (d) Distinguish between mitigation and adaptation.Show worked answer →
A 4-point FRQ on global climate change.
(a) Identify (1 point): any two of rising global average temperature, melting glaciers and ice sheets, rising sea level, ocean warming and acidification, or more frequent extreme weather.
(b) Describe (1 point): shifting species ranges, mismatched timing of life cycles, coral bleaching, or loss of polar habitat.
(c) Explain (1 point): for example the ice-albedo feedback: melting reflective ice exposes dark land or water that absorbs more heat, causing more warming and more melting.
(d) Distinguish (1 point): mitigation reduces the causes (cutting greenhouse gas emissions); adaptation adjusts to the effects (sea walls, drought-resistant crops).
Markers reward two valid evidence points, a valid effect, a correctly explained positive feedback loop, and the reduce-causes versus adjust-to-effects distinction.
AP 2018 (style)1 marksSection I (multiple choice). The ice-albedo feedback accelerates warming because: (A) ice reflects more sunlight as it melts (B) melting ice exposes darker surfaces that absorb more heat (C) ice releases carbon dioxide as it melts (D) darker surfaces reflect more sunlight. Justify your choice.Show worked answer →
A 1-point MCQ on feedback loops. The answer is (B).
In the ice-albedo feedback, warming melts reflective (high-albedo) ice, exposing darker land or ocean (low albedo) that absorbs more sunlight and heat, causing more warming and more melting, a self-reinforcing positive feedback. Reflective ice does not increase as it melts (A), the loop is about absorbed heat not carbon dioxide release (C), and darker surfaces absorb rather than reflect (D). The trap is reversing the albedo logic; dark surfaces absorb, light surfaces reflect.
Related dot points
- 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.
- 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.
- 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.
- 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.
- 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.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)