Earth's climate has warmed
Both natural and human influences have affected climate over the past century, but it is extremely likely that human activities have been the dominant cause of the observed warming since the mid-20th century.
The evidence that climate has changed over the past century includes temperature observations from around the world at the surface and from satellites, over land and sea. In addition, measurements of rainfall, sea levels, and ocean acidity and salinity show identify large scale changes.
Over time, these measurements give us a picture of how climate has changed, both in Australia and globally.
Globally averaged air temperature at the Earth’s surface has warmed by 1.1 °C since reliable records began in 1850.
There is no record of temperature having increased as rapidly as it has over the past century.
Most of the hottest years on record have occurred in the 21st century. Worldwide, every year from 2013 onwards has been among the 10 warmest on record: 2016 and 2019 were the warmest years on record, followed by 2020, 2015, 2017 and 2018.
The heat content of the world's oceans has increased during recent decades and accounts for more than 90 per cent of the total heat accumulated by the land, air and ocean since the 1970s.
On a global scale, the ocean warming is largest near the surface, and the upper 75 m warmed by between 0.09°C and 0.13°C per decade over the period 1971–2010.
As well as temperatures increasing, global average sea levels have risen by around 25 cm since 1880, and there have been large-scale changes to climate, seasonal patterns such as the monsoon, and to the intensity and frequency of extreme weather events.
Changes in Australia
In Australia, land surface temperatures have been recorded at many sites since the mid to late 19th century.
By 1910, Australia had a reliable and standardised network of thermometers. The data they produced have been extensively analysed by the Bureau of Meteorology and scientists at CSIRO, Australian universities and international research institutions.
These high-quality temperature observations reveal that since 1910, Australia's climate has warmed by 1.44 °C (plus or minus 0.24 °C).
This long-term warming trend means that most years are now warmer than almost any year during the 20th century. Since the 1950s, each decade has been warmer than the one before.
We've also experienced an increase in record hot days and a decrease in record cold days across the country. For example, 2019 experienced 43 extremely warm days, more than triple the number in any of the years prior to 2000.
Some years have been relatively cool due to natural effects such as La Niña that partially offset the background warming trend, but overall the trend is clear and distinct: Australia has become warmer.
Rainfall has decreased by around 16 per cent in April to October in the southwest of Australia since 1970. In the southeast of Australia, there has been a decline of around 12 per cent in April to October rainfall since the late 1990s.
Rainfall has increased across most of northern Australia since the 1970s, with a general trend towards increased spring and summer monsoonal rainfall. There has been an increase in the intensity of heavy rainfall events in Australia.
Sea-surface temperatures around Australia have increased faster than the global average, warming by more than 1 °C since 1900, with 8 of the 10 warmest years on record occurring since 2010.