Climate Change and the Enhanced Greenhouse Effect - TCE Environmental Science (Tasmania)
“Explain the greenhouse effect and the enhanced greenhouse effect, and describe the observed and projected impacts of climate change on Tasmanian and global ecosystems.”
The greenhouse effect is a natural process in which gases such as carbon dioxide, methane and water vapour trap outgoing heat and keep Earth warm enough for life. Burning fossil fuels and clearing land have raised greenhouse gas levels, strengthening this trapping in the enhanced greenhouse effect and driving global warming. The result is climate change, which is already shifting Tasmanian ecosystems through warming seas, marine heatwaves, changed rainfall and altered fire patterns.
What this dot point is asking
This dot point asks you to explain how the greenhouse effect works, distinguish the natural effect from the enhanced effect caused by human activity, and describe how the resulting climate change is altering ecosystems. You should name the main greenhouse gases, explain feedback loops, and use Tasmanian and global examples of observed and projected impacts.
The natural greenhouse effect
Energy from the Sun reaches Earth mostly as short-wave radiation. The surface absorbs this energy and re-emits it as longer-wave infrared heat. Greenhouse gases in the atmosphere absorb some of this outgoing heat and re-radiate it in all directions, including back towards the surface. This natural greenhouse effect keeps the planet about 33 degrees warmer than it would otherwise be, making it habitable. The main natural greenhouse gases are water vapour, carbon dioxide, methane and nitrous oxide.
The enhanced greenhouse effect
Human activities have increased the concentration of greenhouse gases. Burning fossil fuels for energy and transport releases carbon dioxide, agriculture and decomposing waste release methane, and clearing forests removes carbon sinks while releasing stored carbon. These extra gases strengthen the heat-trapping effect, so more heat is retained and average global temperatures rise. This human-driven strengthening is the enhanced greenhouse effect, and it is the central cause of modern climate change.
The enhanced greenhouse effect is the additional warming caused when human activities increase the concentration of greenhouse gases, trapping more heat than the natural greenhouse effect alone.
Feedback loops
Climate change is amplified or dampened by feedback loops. A positive feedback loop accelerates warming: as ice and snow melt, the bright surface that once reflected sunlight is replaced by darker ocean or land that absorbs more heat, causing further warming and more melting. Thawing permafrost releasing methane is another positive feedback. A negative feedback loop would dampen change, for example if extra plant growth removed more carbon dioxide, though such effects are generally too small to offset emissions.
Observed and projected impacts
Climate change is not a distant prospect; its effects are already measurable.
The seas around Tasmania are a global warming hotspot. The East Australian Current has strengthened and pushed warmer water further south, raising sea temperatures faster than the global average. This warming, together with marine heatwaves, has driven the spread of the long-spined sea urchin and contributed to the collapse of giant kelp forests along the east coast.
On land, changes to rainfall and temperature are altering fire regimes. Drier conditions raise the risk of bushfire in fire-sensitive ecosystems such as alpine and rainforest communities, including the ancient pencil pine and King Billy pine of the highlands, which do not recover from fire. Globally, climate change is shifting species ranges, disrupting breeding and migration timing, bleaching coral reefs and increasing the frequency of extreme weather.
A common exam trap is to treat the greenhouse effect itself as the problem. The natural greenhouse effect is essential for life. The problem is the enhanced greenhouse effect, the extra warming from human-added gases. Make this distinction clearly to show you understand the mechanism.
Data questions often give a temperature record over time and ask you to quantify and explain the change. Work through it in order.
Calculate the total change
Subtract the earliest value from the latest, for example degrees C, and state the time span over which it occurred.
Put the rate in context
Compare the rate against a benchmark, such as the global average. A rate several times faster marks the region as a warming hotspot.
Explain the mechanism
Link the warming to its cause: a strengthening, southward-extending East Australian Current pushing warm water down the Tasmanian coast, on top of the global enhanced greenhouse effect.
State an ecological consequence
Connect the trend to a measurable effect, such as the spread of the long-spined sea urchin and kelp forest collapse, so the calculation is tied to ecosystem change.
Bringing it together
To answer this dot point well, explain the natural greenhouse effect, then explain how human activity creates the enhanced greenhouse effect, name the key greenhouse gases, and describe at least one feedback loop. Finish with observed and projected impacts, using strong Tasmanian examples such as the strengthening East Australian Current, marine heatwaves, kelp forest collapse and the threat of fire to fire-sensitive alpine flora.
The greenhouse effect and ozone depletion are separate problems. The greenhouse effect traps heat and drives climate change. The ozone hole is the thinning of stratospheric ozone that lets through more harmful ultraviolet radiation. Do not blame climate change on the ozone hole or vice versa.
Exam-style questions
Questions in the style of TASC exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Practice7 marksA dataset shows that east-coast Tasmanian sea surface temperature rose from about degrees C in 1950 to about degrees C in 2020, roughly four times the global average rate. Using the data, calculate the total rise, and explain the ocean process responsible and one ecological consequence.Show worked answer →
A 7 mark data-and-explain question rewards a calculation plus mechanism and consequence.
- Calculate the rise
- degrees C over the period. State that this is about four times faster than the global average, making the region a warming hotspot.
- Explain the ocean process
- The East Australian Current has strengthened and extended further south, pushing warm, nutrient-poor tropical water down the Tasmanian coast and raising sea surface temperatures rapidly.
- State a consequence
- The warming has allowed the long-spined sea urchin to survive and spread south, contributing to the collapse of giant kelp forests; marine heatwaves add further stress. (Range shifts of fish species is also acceptable.)
Markers reward the degree figure, the strengthening East Australian Current, and a valid ecological consequence.
Practice6 marksDistinguish between the natural greenhouse effect and the enhanced greenhouse effect, and explain how a positive feedback loop accelerates warming.Show worked answer →
A 6 mark distinguish-and-explain question wants the contrast plus a feedback mechanism.
The distinction. The natural greenhouse effect is the trapping of outgoing heat by naturally present gases (water vapour, carbon dioxide, methane), keeping Earth about degrees warmer and habitable. The enhanced greenhouse effect is the extra warming caused when human activity raises greenhouse gas concentrations, trapping still more heat.
A positive feedback loop. As warming melts bright, reflective ice and snow, it exposes darker ocean or land that absorbs more solar energy. This causes further warming, which melts more ice, which absorbs still more energy: the change reinforces itself and accelerates.
Markers reward the natural-versus-enhanced contrast and a correctly described self-reinforcing feedback.