the lines of evidence for climate change including direct measurements and proxy data such as ice cores, and the environmental and social impacts of climate change

What this dot point is asking

VCAA wants you to describe the lines of evidence for climate change, distinguish direct measurement from proxy data, and outline the environmental and social impacts. A strong answer explains how a proxy works and gives a real impact, ideally Australian.

Direct measurements

Direct data are recorded with instruments in real time.

• Temperature records. Thermometer records since the mid-1800s show a clear rise in global average surface temperature of more than 1 degree Celsius. Australia's Bureau of Meteorology reports similar warming nationally.
• Atmospheric CO2. Continuous measurements at Mauna Loa (the Keeling Curve) and at Cape Grim in Tasmania show CO2 rising from about 315 parts per million in the late 1950s to over 420 parts per million today.
• Sea level. Tide gauges and satellite altimetry show global sea level rising as oceans warm and expand and land ice melts.
• Ice and snow. Satellite and field data show shrinking Arctic sea ice, retreating glaciers and reduced snow cover.

Proxy data

Proxy data are indirect records preserved in natural materials, used to reconstruct climate before instruments existed.

• Ice cores. Bubbles of ancient air trapped in Antarctic and Greenland ice reveal past CO2 and methane concentrations going back hundreds of thousands of years. The ratio of oxygen isotopes in the ice indicates past temperatures. Ice cores show that today's CO2 levels are higher than at any point in that long record, and that CO2 and temperature have risen together.
• Tree rings (dendrochronology). Ring width reflects growing conditions, allowing reconstruction of past temperature and rainfall.
• Coral cores and sediment cores. Growth bands and chemical composition record past sea temperatures and ocean conditions.
• Pollen records. Pollen preserved in sediments shows how vegetation, and therefore climate, shifted over time.

Feedback loops

Some impacts amplify warming through positive feedback loops. As ice melts, dark ocean or land is exposed, which absorbs more heat and melts more ice (the ice-albedo feedback). Warmer air holds more water vapour, a greenhouse gas, increasing warming. Thawing permafrost releases stored methane and CO2. These feedbacks are a key reason climate change can accelerate.

Environmental impacts

• More frequent and intense heatwaves, droughts and bushfires (the 2019-2020 Black Summer fires in Australia were linked to record heat and dryness).
• Sea-level rise threatening low-lying coasts and Pacific island nations.
• Ocean warming and acidification, driving mass coral bleaching on the Great Barrier Reef.
• Shifts in species distributions as organisms move toward cooler areas; some cannot move fast enough and decline.
• Disrupted timing of natural events such as breeding and flowering.

Social and economic impacts

• Threats to food and water security as droughts and changing rainfall reduce agricultural output, especially in the Murray-Darling Basin.
• Damage to infrastructure and property from fires, floods and storms, raising insurance costs.
• Health impacts from heat stress and changing disease patterns.
• Pressure on First Nations and remote communities whose livelihoods and culture are tied to the land and sea, and displacement of people in vulnerable regions.