About half of the Sun’s energy reaching the top of our atmosphere penetrates to the Earth’s surface as short wave radiation. The rest is either reflected back into space by the atmosphere or absorbed by gases and dust particles. The solar energy that does reach the Earth's surface warms the land and oceans. In turn, the land and oceans release heat in the form of infrared radiation or long wave radiation. See Figure 1.
Figure 1: The greenhouse effect
Greenhouse gases absorb some of this radiation, acting like a blanket and keeping the planet warm enough to sustain life. This is called the natural greenhouse effect.
Throughout history, the Earth's climate has fluctuated naturally– from seasonal variations to sweeping shifts on geological time-scales, like ice ages. However, human activities, predominately the burning of fossil fuels, intensive agriculture and land clearing, are causing greenhouse gas concentrations in the lower atmosphere to rise above natural levels. In effect, the Earth's blanket is becoming thicker, trapping extra heat and further warming the planet. This is called the enhanced greenhouse effect, often referred to as global warming or climate change.
Atmospheric concentrations of carbon dioxide, a key greenhouse gas, are higher now than at any time in the last 420,000 years. These higher concentrations correspond closely to increased rates of fossil fuel consumption and land clearing.
Earth's average temperature might increase by up to 5.8°C over the next 100 years, if greenhouse gas concentrations continue to increase. As the average global temperature rises, it will lead to other changes in weather. Storm patterns and severity might increase, sea levels will rise, and floods and drought may become more frequent and more severe.
Some changes to the climate are inevitable – even if we stop emitting greenhouse gases now, the gases we have already released will have an effect. However, we must do everything we can to avoid further changes, and to adapt to the impacts of climate change.Top of page
A majority of the world's scientists agree that human activities have resulted in observed increase in global average temperatures, particularly since the middle of the 20th century.
Recent data indicates that the global mean temperature has increased by between 0.2 and 0.6°C since the late 19th century, while Australian average temperatures have increased by 0.8°C. The World Meteorological Organisation (WMO) releases a statement each year on the status of the global climate. For 2008, the global mean temperature was 14.3°C, making it the tenth warmest year on record that dates back to 1850.
The Intergovernmental Panel on Climate Change (IPCC) was established by the WMO and the United Nations Environment Programme (UNEP) to assess scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation.
The IPCC's Fourth Assessment Report (2007) concludes that global warming has accelerated in recent decades, and there is new and stronger evidence that warming over the past 50 years is attributable to the increase in greenhouse gas emissions associated with human activities.
The Victorian Government regularly monitors updates in climate change science through the Victorian Climate Change Adaptation Program.
The most recent synthesis for Australia is 'Climate Change 2009: Faster Change and More Serious Risks', often referred to as the Steffen Report, produced by the Australian National University on behalf of the Commonwealth Department of Climate Change.
Key findings from the report show that:
Critical risks for Australia include:
The Copenhagen Synthesis Report was released earlier in 2009 and updates the findings of the 2007 Fourth Assessment by the IPCC and was published in preparation for the UN Climate Change Conference scheduled to take place in December 2009 in Copenhagen. It takes a more global perspective of the implications of new developments in climate change science. Highlights of global risks identified include:
The Department of Sustainability and Environment has prepared a 2-page fact sheet summarising both of these reports which can be downloaded below.
Find out how the climate in each region of Victoria will change under different greenhouse emission scenarios.