Environmental Science and Climate Change
Grade 12 · Science · Study Guide
Examine the science behind Earth's climate system, human impacts on the environment, and strategies for sustainability.
Earth's climate is regulated by a complex system of interactions between the atmosphere, oceans, land, ice, and living organisms. The greenhouse effect is a natural process: solar radiation warms Earth's surface, which emits infrared radiation. Greenhouse gases (CO₂, methane, water vapor, nitrous oxide) absorb this outgoing radiation and re-emit it in all directions, keeping Earth ~33°C warmer than it would otherwise be. Human activities — primarily burning fossil fuels, deforestation, and agriculture — have increased atmospheric CO₂ from ~280 ppm (pre-industrial) to over 420 ppm today, intensifying the greenhouse effect and driving global warming.
Consequences of climate change include rising global average temperatures, melting polar ice and glaciers, rising sea levels, more frequent and intense extreme weather events, ocean acidification (as oceans absorb CO₂, forming carbonic acid), and shifts in species distributions and phenology. The IPCC (Intergovernmental Panel on Climate Change) synthesizes thousands of peer-reviewed studies and projects temperature increases of 1.5–4°C by 2100 depending on emission trajectories.
Beyond climate, environmental science addresses pollution (air, water, soil), habitat destruction, biodiversity loss, ozone depletion (caused by CFCs breaking down stratospheric ozone, increasing UV exposure), and resource depletion. Sustainability involves meeting present needs without compromising future generations' ability to meet theirs. Strategies include renewable energy (solar, wind, hydro), energy efficiency, reforestation, sustainable agriculture, and international agreements like the Paris Agreement.
| Gas | Primary sources | Relative warming potential (100 yr) |
|---|---|---|
| CO₂ (carbon dioxide) | Fossil fuels, deforestation | 1 (baseline) |
| CH₄ (methane) | Livestock, landfills, natural gas | ~84 |
| N₂O (nitrous oxide) | Agriculture, fertilizers | ~265 |
| CFCs/HFCs | Refrigerants, aerosols | Thousands |
Key terms
- Greenhouse effect
- Warming of Earth's surface when atmospheric greenhouse gases absorb and re-emit infrared radiation.
- Carbon dioxide (CO₂)
- Primary anthropogenic greenhouse gas; released by burning fossil fuels and deforestation.
- Global warming
- The long-term increase in Earth's average surface temperature, primarily due to increased greenhouse gases.
- Ocean acidification
- Decrease in ocean pH as oceans absorb CO₂, forming carbonic acid; threatens marine ecosystems.
- Ozone layer
- Layer of ozone (O₃) in the stratosphere that absorbs harmful UV radiation; depleted by CFCs.
- Biodiversity
- The variety of life on Earth at all levels, from genes to ecosystems; essential for ecosystem resilience.
- Sustainability
- Meeting present needs without compromising the ability of future generations to meet their own needs.
Flashcards
- Greenhouse effect
- Natural warming process: greenhouse gases absorb outgoing IR radiation and re-emit it, warming Earth's surface
- Enhanced greenhouse effect
- Human-intensified warming due to increased CO₂, CH₄, N₂O from burning fossil fuels and agriculture
- Ocean acidification
- CO₂ + H₂O → H₂CO₃ (carbonic acid); lowers ocean pH; dissolves coral skeletons; threatens marine life
- Ozone depletion
- CFCs break stratospheric O₃ → O₂; allows more UV-B to reach surface; increases skin cancer risk
- Paris Agreement
- 2015 international treaty; goal to limit warming to 1.5–2°C above pre-industrial levels; 196 signatories
- Carbon footprint
- Total greenhouse gas emissions attributed to an individual, organization, or product, expressed in CO₂ equivalents
Practice questions
Which gas is the most significant anthropogenic contributor to the enhanced greenhouse effect?
- Oxygen
- Nitrogen
- Carbon dioxide
- Argon
Show answer
Answer: Carbon dioxide
CO₂ is the primary anthropogenic (human-caused) greenhouse gas due to the massive scale of fossil fuel combustion, cement production, and deforestation. While methane is more potent per molecule, CO₂ is far more abundant in the atmosphere.
Ocean acidification occurs because oceans absorb CO₂, which forms carbonic acid.
Show answer
Answer: True
When oceans absorb CO₂, it reacts with water to form carbonic acid (H₂CO₃), which dissociates and lowers ocean pH. Since industrialization, ocean pH has dropped from ~8.2 to ~8.1 — a 26% increase in acidity.
The stratospheric ___ layer absorbs harmful UV radiation and is depleted by CFCs.
Show answer
Answer: ozone
The stratospheric ozone layer (primarily 15–35 km altitude) absorbs 97–99% of UV-B and UV-C radiation. Chlorofluorocarbons (CFCs) catalytically destroy ozone; the 1987 Montreal Protocol began phasing them out.
Pre-industrial atmospheric CO₂ levels were approximately:
- 180 ppm
- 280 ppm
- 380 ppm
- 420 ppm
Show answer
Answer: 280 ppm
Pre-industrial CO₂ was approximately 280 ppm, stable for thousands of years. It began rising sharply with industrialization in the mid-1800s and has now exceeded 420 ppm — the highest in at least 800,000 years.
Renewable energy sources include solar, wind, and nuclear power.
Show answer
Answer: False
Nuclear power uses nuclear fission (not an infinitely renewable process — uranium is finite) and is generally classified separately as 'low-carbon' rather than 'renewable.' Solar, wind, hydro, geothermal, and biomass are renewables.
Fun facts
- The 2023 global average temperature was ~1.45°C above the pre-industrial baseline — the hottest year in recorded history, surpassing the previous record set in 2016.
- The Great Pacific Garbage Patch is roughly twice the size of Texas — a vortex of plastic debris trapped by ocean currents, with an estimated 80,000 metric tons of plastic.
- If all Antarctic ice melted, sea levels would rise approximately 58 meters — enough to submerge most of the world's major coastal cities.
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