To understand climate change, it’s important to recognise the difference between weather and climate. Weather is a mix of variables – things like rainfall, temperature and humidity - that occur each day and vary from place to place.

Climate is a statistical description of weather patterns for a region, including both averages and extremes over time. Weather variables such as temperature and rainfall fluctuate naturally. While weather changes on a daily basis, the climate changes relatively slowly. The period for estimating climate is usually 30 years or more, long enough to sample a full range of weather fluctuations.

Climate is a statistical description of weather patterns for a region, including both averages and extremes over time. Weather variables such as temperature and rainfall fluctuate naturally

The global climate has changed dramatically since the Earth was formed 4.5 billion years ago. In the last 1 million years, the Earth’s average surface temperature has fluctuated by about 5 degrees Celsius, through 10 major ice age cycles. However, geological evidence suggests that these changes occurred slowly over tens of thousands of years compared with the relatively rapid warming of the past 100 years.

Global average temperature has increased over the 100 years to 2009 by more than 0.7 degrees Celsius. Measured warming over the past 50 years was nearly twice that for the past 100 years. The last decade has been the warmest on record. Changes in the Australian and Victorian climates have matched the global trend.

No. 1998 was an extremely warm year but the overall warming trend has continued over the past decade.

Climate varies naturally on many timescales. A well-known example of this is the El Nino oscillation which influences temperatures and rainfall patterns throughout the Pacific region and beyond.

In principle, a natural fluctuation could last for decades. However evidence going back up to 20 centuries does not show variations in global temperature resembling those that have taken place in the last 100 years.

No. The combined annual emissions from volcanoes averaged over several decades are less than 1% of CO2 emissions in 2009 from fossil fuels, industrial processes and deforestation.

A balanced assessment of the available evidence and prior knowledge allows us to attach levels of confidence to the findings of climate science. The broad conclusions of climate change science are based on many lines of evidence which give a high degree of confidence.

These questions and answers have been based on information in The Science of Climate Change: Questions and Answers, published by the Australian Academy of Science.

The publication gives and up to date explanation of the current situation in climate science, including where there is consensus in the scientific community and where uncertainties exist.