Notes
Stratospheric ozone depletion
- Ozone in the stratosphere absorbs harmful UV-B radiation.
- CFCs (old refrigerants and aerosols) rise to the stratosphere, where UV releases chlorine atoms. One chlorine atom can destroy thousands of ozone molecules.
- More UV means more skin cancer, cataracts and harm to plants and plankton.
- The Montreal Protocol (1987) phased out CFCs, and the ozone layer is slowly recovering. Replacements like HFCs don't harm ozone but are strong greenhouse gases.
The greenhouse effect and climate change
- Greenhouse gases absorb infrared radiation (heat) given off by Earth and re-radiate it, warming the planet. Without the natural greenhouse effect, Earth would be frozen.
- Main gases: $\mathrm{CO_2}$ (fossil fuels, deforestation), methane ($\mathrm{CH_4}$, from livestock, landfills, rice paddies, natural gas leaks), nitrous oxide ($\mathrm{N_2O}$, fertilizers), water vapor, and CFCs/HFCs.
- Global warming potential (GWP) compares gases to $\mathrm{CO_2}$. Methane traps much more heat per molecule but stays in the air for a shorter time.
- Evidence: rising $\mathrm{CO_2}$ (the Keeling curve), rising average temperatures, melting glaciers and sea ice, and rising sea levels.
- Effects: sea-level rise (thermal expansion and melting land ice), more intense heat waves and storms, shifting species ranges, spread of diseases, and ocean warming that causes coral bleaching.
- Positive feedback loops: melting ice exposes darker water and land, which absorb more heat (lower albedo); thawing permafrost releases methane.
Ocean acidification
The oceans absorb $\mathrm{CO_2}$, which forms carbonic acid and lowers pH. This makes it harder for corals, shellfish and plankton to build calcium carbonate shells.
Invasive species and endangered species
- Invasive species spread quickly in new places without natural predators (zebra mussels, kudzu, cane toads). They are often r-selected generalists.
- Threats to biodiversity: HIPPCO (Habitat loss, Invasive species, Population growth, Pollution, Climate change, Overexploitation). Habitat loss is the biggest.
- Protections: the Endangered Species Act, CITES (limits trade in endangered species), protected areas and habitat corridors.
Practice
UV releases chlorine from CFCs, which breaks down ozone.
It phased out CFCs and similar chemicals.
They trap outgoing heat.
Methane comes from anaerobic decomposition and livestock.
Lower albedo is a positive feedback.
Dissolved $\mathrm{CO_2}$ lowers ocean pH.
r-selected generalists without predators spread quickly.
Habitat destruction affects the most species.
Free response
Write your answer first, then open the scoring guide.
Free-response question
Atmospheric $\mathrm{CO_2}$ has risen from about 315 ppm in 1958 to about 420 ppm today.
(a) Calculate the percent increase.
Show the answer and scoring guide
$\displaystyle \frac{420 - 315}{315} \times 100 \approx 33\%$.
Check off the points you earned:
(b) Identify two human activities that contribute to rising $\mathrm{CO_2}$.
Show the answer and scoring guide
Burning fossil fuels for electricity and transportation, and deforestation (fewer trees to absorb $\mathrm{CO_2}$, and burning or decay releases stored carbon).
Check off the points you earned:
(c) Describe one effect of rising $\mathrm{CO_2}$ on coral reefs.
Show the answer and scoring guide
Ocean acidification makes it harder for corals to build their calcium carbonate skeletons; warming also causes coral bleaching.
Check off the points you earned: