Year 9 answers
Greenhouse basics
- (i) Sunlight reaches Earth’s surface. (ii) The warm surface emits infrared radiation. (iii) Greenhouse gas molecules absorb some of this infrared. (iv) They re-emit it in all directions, including back down, warming the lower atmosphere and surface.
- E.g. CO - burning fossil fuels; CH - livestock, gas leaks, rice paddies; NO - fertiliser use; water vapour - evaporation; CFC/HFC - refrigeration/industrial.
- The natural effect keeps Earth habitable ( average). The enhanced effect is the extra warming caused by human-added greenhouse gases raising their atmospheric concentrations.
- Any four of: rising global temperature; ice core CO and temperature records; shrinking glaciers and sea ice; rising sea level; ocean acidification; shifts in species ranges and flowering times.
- “ppm” means parts per million, so 420 ppm means 420 molecules of CO in every million air molecules. Current level about 420 ppm.
- Warming melts ice/snow; darker exposed ocean or land absorbs more sunlight, causing further warming (positive feedback).
Apply the ideas
- Without greenhouse gases, more of the infrared Earth emits would escape directly to space. The balance between absorbed solar energy and emitted infrared would then sit at a much colder surface temperature (around ).
- Water vapour concentration is controlled by temperature (warmer air holds more); it cannot be directly managed. It acts as a feedback, amplifying warming triggered by CO and other long-lived gases, which we can manage.
- Weak argument. Small concentrations can still absorb strongly at specific infrared wavelengths. CO’s greenhouse effect is well measured in lab and field; doubling CO roughly doubles the added radiative forcing.
- Snowfall traps tiny air bubbles as it is buried and compressed into ice. Drilling cores and analysing the bubbles reveals CO, methane, and isotope records going back hundreds of thousands of years.
- Mitigation reduces the cause (e.g. switch to renewables). Adaptation adjusts to the impacts (e.g. build sea defences).
Data and responses
- mm m over 100 years. For a suburb at 1 m, a third of that elevation is lost, and storm surges plus high tides would already flood much of the area — plus feedback from rapid ice-sheet loss could make the rise larger.
- Rise: ppm. Percentage: .
- Mitigation — solar electricity replaces fossil-fuel generation, cutting CO emissions.
- Typical ranking (large to small): EV on renewables and flying less tend to be large; reducing red meat is sizable (methane, land use); LED lights give meaningful but smaller savings. Exact order depends on household baseline, but flying and vehicle fuel usually dominate.
Challenge
- Arctic permafrost contains huge quantities of organic carbon. As air warms, permafrost thaws; microbes decompose the organic matter, releasing CO and methane. These gases cause further warming and more thawing — a positive feedback that could lock in warming even if human emissions were stopped.
- Dissolved CO + water -> carbonic acid, which lowers ocean pH and reduces carbonate ions needed for shells and coral skeletons. Shell-forming organisms (plankton, molluscs, corals) are weakened, threatening food webs. Called the “other CO problem” because acidification is distinct from, but caused by the same CO that drives, climate warming.
- Volcanoes cause short-term cooling from sulfate aerosols, not warming. Solar output has been roughly flat since 1970. Milankovitch cycles act on tens of thousands of years, not decades. None matches the timing or magnitude of the post-1970 rise, while CO forcing does.
- Counter-arguments: (i) Australia has high per-capita emissions, so “small” is misleading. (ii) Climate change is a collective action problem — if every country said “we are small”, global emissions never fall. (iii) Australia is particularly exposed to climate impacts (droughts, bushfires, Great Barrier Reef), so mitigation protects self-interest. (iv) Leadership and export economics — clean-tech and renewables trade will favour early movers.