What is climate change?

What is climate change?

Climate change is a change in the average pattern of weather over a long period of time. Weather is the short-term observation of rainfall, temperature and winds. Climate is the long-term statistical average of weather, described according to rainfall patterns and average temperatures.

The majority of scientists now agree that the world's climate is changing because of an increase in atmospheric carbon dioxide concentrations.  According to the Editor-in-Chief of Science Magazine, "Consensus as strong as the one that has developed around this topic is rare in science."

To understand how the climate is changing and why, we draw from CSIRO's "Understanding Climate Change" factsheet.

Our climate is changing

In the past century, the global average surface temperature has risen by 0.74 ºC. The observed increase in average temperatures is widespread around the globe, with rising trends recorded on all continents and in the oceans.

The Earth is warming

Globally, observed CO2 emissions, temperature and sea levels are rising faster than expected. The warming has been fastest over land, and greatest in the higher latitudes of the northern hemisphere. Global ocean temperature rose by 0.10 ºC between 1961 and 2003, to a depth of 700 metres. In Australia, there has been a 0.9 ºC warming since 1950. We have already observed changes to our climate that are more rapid than anything the earth has experienced for at least 1800 years.

Change is happening now - results include:

  • Retreat of glaciers and sea-ice
  • A decline of 10-15% of the Arctic sea ice extent and a 40% decrease in its average thickness
  • Snow depth at the start of October has declined 40 per cent in the last 40 years in the Australian Alps
  • An average sea level rise of 20 mm per decade over the last 50 years
  • Changes in mating and migration times of birds
  • Pole-ward and altitudinal shifts of plants and animals (especially in the Alpine zone)
  • An increase in coral bleaching due to increased water temperature.


CSIRO Fast facts

  • Global average surface temperature has risen by 0.74 ºC over the past century.
  • Greenhouse gas concentrations in the atmosphere have increased since 1750, and now exceed pre-industrial levels.
  • There is greater than 90 per cent likelihood that most of the global warming seen since the mid 20th-century is due to increases in greenhouse gas emissions.
  • Sea level is projected to rise further by the end of this century.


Our climate will continue to undergo natural change coupled with changes due changes to atmospheric greenhouse gas concentrations. Three factors will determine the amount and speed of future climate change.

  • First, whether greenhouse gases and aerosol concentrations increase, stabilise or decrease.
  • Second, how strongly features of the climate (temperature, precipitation, and sea level) respond to changes in greenhouse gas and aerosol concentrations.
  • Third, how much the climate varies as a result of natural influences (volcanic activity and changes in the sun's intensity), and its internal variability (changes in the circulation of the atmosphere and oceans).


To find out more about why climate scientists believe this is happening and possible consequences, you can see the Intergovernmental Panel on Climate Change (IPCC)'s Frequently asked questions.