After a natural disaster
A single volcano in the Philippines once cooled the entire planet by half a degree for two years. Disasters don't just damage — they ripple through the living world and the air long after the event, and a local catastrophe can reach the whole globe. This powerbook follows that reach: how eruptions change the climate both ways, what extreme weather does to ecosystems, and how our own hands make some disasters worse.
The interactive book above is the lesson. What follows is a plain recap you can revise from, plus the sources and how this maps to the syllabus.
Eruptions and climate
Effusive eruptions (lava) hit locally and at ground level; explosive ones blast ash and gas high, reaching regional and global scale. A big eruption changes climate both ways: short-term cooling as stratospheric sulfate aerosols (from SO2) reflect sunlight; long-term warming from accumulated CO2. For one eruption, cooling wins.
Pinatubo, 1991
Injected ~20 million tonnes of SO2 into the stratosphere; the global aerosol veil cooled the planet by about 0.5°C for one to two years and thinned the ozone layer. Locally, ash and lahars devastated ecosystems; globally, diffuse light briefly boosted photosynthesis. A measured demonstration of one eruption reshaping the whole planet, then recovering.
Extreme weather and the human hand
Hailstorms, east coast lows, ENSO-driven droughts and floods, and bushfires reshape ecosystems — fire being double-edged (natural and renewing, but devastating when severe). Humans raise the frequency and magnitude of some: clearing and paving worsen floods; ignition, fuel and a hotter climate worsen bushfires; stripping and cutting slopes trigger landslides.
For HSC students
This powerbook covers the Impact of Natural Disasters on the Biosphere thread of Module 6 (Hazards), framed by the inquiry question how do natural disasters influence the biosphere and atmosphere? Working through it, you should be able to:
- compare explosive and effusive eruptions in terms of impact on the biosphere and atmosphere;
- analyse how a major eruption changes climate — both cooling and warming;
- assess a case study (Mount Pinatubo) of an eruption with significant effects on the biosphere and atmosphere;
- evaluate climatic phenomena (hailstorms, east coast lows, droughts/floods, bushfires) on local ecosystems, and how human activity raises the frequency and magnitude of droughts/floods, bushfires and landslides.
The next chapter looks at predicting natural disasters and reducing their effects. Explanations here are original and are a study aid, not a copy of the syllabus.
Sources
- US Geological Survey and NASA — the 1991 Mount Pinatubo eruption, its stratospheric aerosols and global cooling.
- Published climate science — volcanic sulfate aerosols (cooling), volcanic CO2 (long-term warming), and diffuse-light effects on photosynthesis.
- Australian Bureau of Meteorology — east coast lows, hailstorms, droughts and floods, and the El Niño–Southern Oscillation.
- CSIRO and fire-ecology research — bushfire as a natural force, fire-adapted vegetation, and human influence on fire, flood and landslide risk.
- NSW NESA Earth and Environmental Science Stage 6 Syllabus (2017) — used only to scope the Module 6 content; explanations above are original.
One eruption can chill a planet; one fire season can reshape a forest. Disasters reach far beyond the moment they strike — and increasingly, our own hands help decide how hard they land.