Responding to global change

Working together

The atmosphere and oceans belong to everyone, so no country can fix a global problem alone. If one country cuts its pollution while others don't, it bears the cost and everyone shares the benefit, so global problems need global agreements. The best example is the Montreal Protocol, which phased out the CFCs that were destroying the ozone layer (you studied the chemistry in 4E). Every country in the world has signed it, and the ozone layer is on track to recover by around the 2060s.

• UN Framework Convention on Climate Change (1992): agreed at the Rio Earth Summit; countries promised to prevent "dangerous" interference with the climate. Its yearly meetings are called COPs.
• Kyoto Protocol (1997): set binding targets for developed countries only. Australia ratified it in 2007.
• Paris Agreement (2015): almost every country agreed to keep warming "well below 2 °C" and to try to limit it to 1.5 °C. Each country sets its own target (its "nationally determined contribution") and must update it every five years with more ambition.
• Kigali Amendment (2016) to the Montreal Protocol: phases down HFCs, the replacements for CFCs, which don't harm ozone but are powerful greenhouse gases.
• COP28 (2023): for the first time, countries agreed to "transition away from fossil fuels in energy systems".

The carbon budget

Because CO₂ lasts for centuries, warming depends on the total amount ever emitted. That means there is a limited "carbon budget" left for any temperature goal.

From the start of 2025, the budget for a 50% chance of staying at 1.5 °C was only about 130 billion tonnes of CO₂, around three years of current emissions. The budget for 2 °C is several times larger. This is why scientists say global emissions need to fall roughly by half by the 2030s and reach net zero (any remaining emissions balanced by removals, such as growing forests) around mid-century.

Australia's emissions and targets

Australia produces about 1% of the world's emissions, but per person they are among the highest in the world, mainly because of coal-fired electricity, long driving distances, livestock and mining. Australia is also one of the largest exporters of coal and gas, whose emissions are counted in the countries that burn them. Under the Climate Change Act 2022, Australia's targets are to cut emissions to 43% below 2005 levels by 2030 and reach net zero by 2050. In 2025 the government added a 2035 target of 62–70% below 2005.

By 2024 emissions were about 440 million tonnes of CO₂-equivalent, roughly 28% below 2005, mostly thanks to less land clearing and more renewable electricity. Renewables supplied about 40% of Australia's electricity in 2024, and the national goal is 82% of the main grid by 2030.

Caring for Country

First Nations land and sea management is one of Australia's most important environmental responses. Indigenous Protected Areas now make up about half of the National Reserve System, Australia's network of protected land, and Indigenous ranger groups manage fire, weeds, feral animals and threatened species across millions of hectares. You looked at savanna burning, which cuts emissions and earns carbon credits, in Year 9 (3H), and at First Nations clean energy projects in Year 9 (6G).

Waste in global systems

Many of the things we throw away travel through all four spheres. Plastics break into microplastics that drift on currents (7B), enter food webs and have been found from the deep sea to Antarctic snow. On Lord Howe Island, scientists studying flesh-footed shearwaters found that chicks fed plastic by their parents developed scarred, damaged stomachs. In 2023 they named this new disease plasticosis. Organic waste rotting in landfill produces methane, which is why councils now collect food and garden waste for composting, and many landfills capture their methane to generate electricity.

E-waste (old phones, computers and appliances) is one of the fastest-growing kinds of waste. It contains toxic metals such as lead and mercury, but also gold, silver, copper and rare earth elements. A tonne of old phones contains far more gold than a tonne of typical gold ore, so recycling e-waste ("urban mining") protects the lithosphere and biosphere and creates jobs.

Back from the brink

Responses can work. The Lord Howe Island stick insect, a large, flightless phasmid as long as your hand, was wiped out on Lord Howe Island after black rats came ashore from a shipwreck in 1918. In 2001 a small population was rediscovered clinging to a single shrub on Ball's Pyramid, a sea stack 23 km away. Melbourne Zoo bred thousands from just a few insects, and after an eradication program removed the rats and mice from Lord Howe Island in 2019, scientists began preparing to return the insects to their home.