Briefing paper: Climate Change


Just the facts about the planet warming.

Global warming is defined as an increase in the Earth’s surface temperature caused by rising concentrations of greenhouse gases.

The greenhouse effect, meanwhile, is a naturally occurring phenomenon that helps make life on our planet habitable. Without it, surface temperatures would be about 33°C lower than they are.

According to climate scientists, however, global warming (a term sometimes used interchangeably with “climate change”) is magnifying this phenomenon, increasing carbon in the atmosphere, and raising average temperatures around the globe.

Indeed, it’s estimated that average global temperatures have risen by as much as 0.8°C since 1880, when records first started. Although this doesn’t sound like all that much, the Earth is a delicate system, and the ripple effects of even small changes are profound.

These include greater frequency of extreme weather events such as cyclones, blizzards, hurricanes, wildfires, extreme-heat days and droughts; the melting of polar ice caps and glaciers; the rising of ocean levels; and the disruption of ocean currents such as the Gulf Stream, among other major impacts.

Using sensors located around the world, and comparing results with historical data, climate scientists tell us the evidence for the impact of climate change is clear and compelling.

“Cold and hot, wet and dry – we experience natural weather conditions all the time,” says Texas Tech University climate scientist Katherine Hayhoe. “But today, climate change is loading the dice against us, making certain types of extremes, such as heatwaves and heavy rain events, much more frequent and more intense than they used to be.”

The 20 hottest years on record have all occurred in the past 22 years. And only three years – 2016, 2015 and 2017 – were hotter than 2018.

2018 was the hottest year on record for the planet’s oceans, which are heating up more quickly than has been estimated.

Scientists have warned of dire consequences unless action is taken immediately to reduce our carbon emissions.

The Paris agreement, an international climate treaty, aims to limit global temperatures rises to less than 2°C. Scientists say that any more than this will see the planet experience dramatic, irreversible changes that make life for humans much less hospitable.

Australia’s Bureau of Meteorology (BOM) has confirmed that the summer of 2018–19 was the hottest on record. The average national temperature across the country was up by 2.14°C. It was also 1.28°C hotter than the previous record, set in the summer of 2012–13.

New South Wales, Victoria, Western Australia and the Northern Territory all experienced their hottest summer on record. For Tasmania and South Australia it was the second warmest, and for Queensland the fourth warmest – partly due to flooding rains in that state during late January and early February.

Adelaide set a record temperature of 46.6°C. In Port Augusta, 300km northwest of the capital, it topped out at 49.5°C.

Different sites in NSW also new records, including Borrona Downs, which went through one night with a minimum of 36.6°C. Nationally, the average minimum temperature broke the record by 1.67°C.

“There’s been so many records it’s really hard to count,” says the BOM’s senior climatologist Andrew Watkins.

It was also the driest summer on record for parts of Australia. Dust storms from Central Australia affected the east on several occasions – one storm in mid-February stretched over 1,500km.

“Summer 2018–19 comes on the back of a string of warm months and warm seasons for Australia,” says the BOM. “This pattern is consistent with observed climate change. As the State of the Climate 2018 report outlines, Australia has warmed by more than 1°C since 1910, with most warming occurring since 1950. This means that natural climate variability sits on top of this background warming, and temperature records are likely to continue to be broken in the coming years.”

About the same time as the Australian electorate rejected serious action on climate change, scientists in the US detected the highest levels of planet-warming CO2 in the Earth’s atmosphere since records began.

The Mauna Loa Observatory in Hawaii, which has tracked atmospheric CO2 levels since the late 1950s, detected 415.26 parts per million in early May. It was the first time on record that the observatory measured a daily baseline above 415 ppm.

The last time Earth’s atmosphere contained this much CO2 was more than three million years ago, when global sea levels were several metres higher and parts of Antarctica were covered in lush forest.

“It shows that we are not on track with protecting the climate at all,” says Wolfgang Lucht from the Potsdam Institute for Climate Impact Research. “The number keeps rising, and it’s getting higher year after year. This number needs to stabilise.”

Levels of CO2 – one of three greenhouse gases produced when fossil fuels are burnt – are climbing at a rapid pace.

And 2019 is likely to be an El Niño year in which temperatures rise due to warmer ocean currents.

“All of human history has been in a colder climate than now,” Lucht says. “Every time an engine runs, we emit CO2, and it has to go somewhere. It doesn’t miraculously disappear; it stays in the atmosphere.”

Despite the Paris agreement the past four years have been the hottest on record.

“We’re on a runaway train,” says leading climatologist Dr Peter Gleick. “Scientists are blowing the whistle, but politicians are shovelling coal into the engine.”