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.
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What this topic is asking
The College Board (Topic 9.4) wants you to identify the human activities that increase greenhouse gases and explain why their concentrations are rising.
The main human sources
How deforestation raises carbon dioxide
Why concentrations are rising
Why this matters
Topic 9.4 connects the greenhouse effect (Topic 9.3) to its human causes, tying Unit 9 back to fossil fuels (Unit 6), deforestation (Unit 5) and the carbon cycle (Unit 1). The Keeling Curve is a standard AP exam data figure, and the two-way effect of deforestation is a frequently tested explanation.
Try this
Q1. Identify the largest human source of carbon dioxide emissions. [1 point]
- Cue. Burning fossil fuels (coal, oil and natural gas).
Q2. Explain how deforestation increases atmospheric carbon dioxide. [2 points]
- Cue. Deforestation removes trees that would absorb carbon dioxide, shrinking the carbon sink, and burning or decay of the cleared trees releases their stored carbon, adding a source, so it both lowers uptake and raises emissions.
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 2022 (style)4 marksSection II (FRQ). (a) Identify the human activity that contributes the most carbon dioxide. (b) Identify two human sources of methane. (c) Explain how deforestation raises atmospheric carbon dioxide in two ways. (d) Describe the evidence that carbon dioxide is rising.Show worked answer →
A 4-point FRQ on rising greenhouse gases.
(a) Identify (1 point): burning fossil fuels (coal, oil, natural gas) for energy, transport and industry.
(b) Identify (1 point): any two of livestock (enteric fermentation), rice paddies, landfills, and natural gas leaks.
(c) Explain (1 point): deforestation removes trees that absorb carbon dioxide (reducing the sink), and burning or decay of the cleared trees releases stored carbon (adding a source).
(d) Describe (1 point): direct measurements (the Keeling Curve) show a steady rise in atmospheric carbon dioxide since the 1950s, with ice cores showing today's levels far above pre-industrial values.
Markers reward fossil-fuel combustion as the main carbon dioxide source, two valid methane sources, the both-removes-sink-and-adds-source effect of deforestation, and the direct-measurement (Keeling Curve) evidence.
AP 2018 (style)1 marksSection I (multiple choice). The largest single human source of carbon dioxide emissions is: (A) volcanic eruptions (B) the burning of fossil fuels (C) animal respiration (D) ocean release. Justify your choice.Show worked answer →
A 1-point MCQ on greenhouse gas sources. The answer is (B).
Burning fossil fuels for energy, transport and industry is the largest human source of carbon dioxide, releasing carbon stored underground for millions of years. Volcanoes (A) emit far less than human activity, and respiration (C) and ocean release (D) are natural fluxes balanced by uptake. The trap is overstating natural sources; human fossil-fuel combustion is the dominant driver of the rise.
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 9.5 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.
- Topic 1.4 The Carbon Cycle: describe the major reservoirs and fluxes of the carbon cycle and explain how natural processes and human activities move carbon between them.
A focused answer to APES Topic 1.4, covering carbon reservoirs and fluxes, photosynthesis and respiration, decomposition, combustion, the ocean as a carbon sink, and how fossil fuel burning alters the cycle, with a worked carbon-flux calculation.
- Topic 6.5 Fossil Fuels: explain how fossil fuels form and are used to generate electricity, and describe their environmental impacts, including cogeneration.
A focused answer to APES Topic 6.5, covering how fossil fuels form, how a fossil-fuel power plant generates electricity, fracking, cogeneration, and the environmental impacts of coal, oil and gas, with a worked power plant efficiency calculation.
- Topic 5.2 Clearcutting: describe clearcutting and explain its environmental consequences for soil, water and ecosystems.
A focused answer to APES Topic 5.2, covering clearcutting as a logging method, its economic appeal, and its consequences for soil erosion, water temperature and quality, flooding, habitat loss and biodiversity, with a worked erosion comparison.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)