What is climate change?
Climate change is any significant change in the measures of climate lasting for several decades or longer, including changes in temperature, precipitation or wind patterns. Historically the Earth’s climate has changed continually, but it is widely agreed that the observed changes over the past 50 years or so have been primarily caused by human activities.
How much has the global temperature changed?
Long-term air and ocean temperature records clearly show the Earth is warming. Over the past century, the global air temperature has increased by about 0.8ºC. From about 1970 the global air temperature trend has strongly increased.
The oceans are absorbing around 90% of the additional heat, with ocean heat content showing strong increases; on average the temperature of the ocean layer from 0 to 700 metres increased by 0.18ºC between 1955 and 2010.
Why does only a few degrees of warming matter?
Warming of a few degrees in average temperature may seem minor, but it is much larger than any other climatic changes experienced in the past 10,000 years. The increase in average temperature creates a much greater likelihood of very hot weather and a much lower likelihood of very cold weather. A warming of only a few degrees in average temperatures means we will see weather events that have never been observed since instrumental records were begun, and heat events that were rare in the previous climate will become more common. For comparison, the difference in average air temperature between an ice age and a warm period in recent Earth history is only 5 to 6ºC.
How does climate change affect us?
Changes have already been observed in our climate and have caused serious impacts in Australia. There has been an increase in the number of hot days and record-breaking heatwaves and in heavy rainfall events.
Climate change is likely to continue to affect Australians in a number of ways, including:
- rising temperatures and more hot days
- greater risk of bushfire
- increased frequency and severity of extreme weather events including heavy rainfall and drought
- sea-level rise leading to more coastal flooding and erosion.
Specific impacts will vary according to location. Before relaunching as the community-funded Climate Council, the Climate Commission produced a number of state and regional reports for communities across Australia, which can be found on our Reports page.
Why is the climate changing?
Greenhouse gases, including carbon dioxide, are a natural part of the atmosphere. These gases act like a blanket, trapping some of the sun’s heat close to the Earth’s surface and keeping the planet warm enough for us to live. This is known as ‘the greenhouse effect’.
The natural greenhouse effect is being influenced by human activity. Humans are using increasing amounts of energy to power our modern way of life, for example, to power cars, planes, factories, computers and televisions. Much of this energy is generated by burning fossil fuels (coal, oil and natural gas). The burning of fossil fuels adds carbon dioxide and other greenhouse gases to the atmosphere. As more greenhouse gases are added to the Earth’s natural blanket, more of the sun’s heat is trapped and this causes the Earth’s average temperature to rise.
Since the Industrial Revolution (in the mid-1700s), carbon dioxide levels in the atmosphere have increased by 40% and are now the highest they have been for 800,000 years.
Deforestation also has an impact. Trees and plants store carbon in their branches, leaves, trunks and roots. When trees are cut down or burnt this carbon is released into the air as greenhouse gases.
Scientists study the past changes in the Earth’s climate, such as through ice cores, and have found that no natural processes can explain the extra heat in the Earth’s atmosphere and oceans.
How do scientists know the climate is changing?
Scientists collect detailed and accurate data on the climate system, including air and ocean temperature, precipitation, sea level, ocean salinity and acidity, changes in ice sheet mass, to name just a few.
Direct measurements of temperature and precipitation have been taken for over 150 years. Since the 1970s satellites have measured global temperatures and since the 1990s global sea level. Proxy records such as ice cores, tree rings, marine sediments, pollen and others provide insights into the climate of hundreds or thousands of years ago.
Analysis of this climate data is used to put today’s climate change in a longer term context and to explore the response of the climate system to changes in radiative forcing in the past.
The most significant difference between recent warming and previous changes in the Earth’s climate is the speed of the change and the role of humans in changing greenhouse gas concentrations. Ice cores from Antarctica provide a record of 800,000 years of atmospheric carbon dioxide; in all that time the concentration has never increased so quickly and by so much as during this era of human influence.
How can we deal with climate change?
To have a good chance of keeping global temperatures from rising above 2ºC on pre-industrial levels, we can emit no more than 1,000 billion tonnes of carbon dioxide from 2000 to mid-century. After the carbon budget is spent the economy must be completely decarbonised.
This will require a progressive shift away from fossil fuels to technologies that use low emission power, including renewable energy and increasing energy efficiency. The earlier such action is under way the less disruptive and costly it will be.
Although there’s a long road ahead, we will all benefit from a move towards more renewable energy, cleaner air, better health and new industries.
We can all contribute to creating a more sustainable Australia. Our Solutions section has more information.
Where can I find out more?