About climate change
Geology and fossil records show ample evidence that the climate of the earth has always been in flux, and has changed naturally on time scales ranging from years to millennia as a result of natural processes. What is concerning us now is that the rate of change has been accelerating since the 1950s.
The earth is getting warmer—so sea levels are rising, glaciers and sea ice are melting, and the global climate is becoming more variable, with changed rainfall patterns and an increase in intense weather events such as storms and cyclones.
This warming is unequivocal, according to the Intergovernmental Panel on Climate Change (IPCC), which provides authoritative scientific information from the world’s leading climate scientists and climate modelling systems.
In its Fourth Assessment Report released in 2007, the IPCC reports that:
- Most of the warming in the past 50 years is “very likely” (more than 90% in probability) due to the observed increase in greenhouse gas concentrations from human activities such as the burning of fossil fuels and land use change.
- Global average surface temperature increased by 0.7ºC, and global sea level rose approximately 17cm in the last century (to 2005).
Changes in climate are being experienced across Australia. Regional climate change projections for Australia and Queensland are produced by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Australian Bureau of Meteorology and are based upon the latest international climate change research including conclusions from the IPCC Fourth Assessment Report (2007).
In its latest report Climate Change in Australia — Technical Report 2007, the CSIRO and Australian Bureau of Meteorology reported that Australian average temperatures have warmed by 0.9ºC since 1950.
Climate Change in Queensland: What the science is telling us
The Office of Climate Change in the Queensland Government has prepared a document – Climate Change in Queensland: What the science is telling us (PDF, 2.1MB)* – that analyses international and national climate change science and assesses its significance to Queensland's regions and sectors. The report draws on two main sources: the IPCC Fourth Assessment Report and the CSIRO and Australian Bureau of Meteorology Climate Change in Australia — Technical Report 2007.
Effect of human activities
Though natural processes affect climate change, it is also apparent that human activities are having a real and observable influence. Current studies at QCCCE are aimed at isolating the likely effects of factors related to these activities because:
- the factors will change in different ways in the future
- each has a different impact on global climate.
The main effects of human activity on climate change are:
- Increased emissions of greenhouse gases
- Depletion of stratospheric ozone
- Increase in sulphate aerosols over Asia
- Land-cover change
Increased emission of greenhouse gases
The presence in the atmosphere of greenhouse gases such as carbon dioxide (CO2), methane, nitrous oxide, and halocarbons (e.g. chlorofluorocarbons (CFCs)) is natural—by trapping heat from the sun they play a role in regulating the earth’s temperature. However, their level in the atmosphere is increasing as a result of human activity. This is driving the phenomenon known as the 'enhanced greenhouse effect', which is a major factor causing global warming—and these levels will continue to rise.
Both international studies and modelling studies conducted by the QCCCE indicate that increased atmospheric levels of CO2 have tended to enhance summer rainfall in eastern Australia. However, the effect of this on our future rainfall is uncertain, because this also depends strongly on changes in large-scale circulation patterns in the Southern Hemisphere (e.g. the El Niño-Southern Oscillation or the Southern Annular Mode). These vary naturally from year to year, and also over decades, but are also influenced by changes in concentration of greenhouse gases.
Depletion of stratospheric ozone
Another factor causing climate change is depletion of stratospheric ozone over the poles as a result of increased levels of CFCs in the atmosphere. This has lead to marked changes in atmospheric circulation patterns in both the northern and southern hemispheres. However, levels of CFCs in the atmosphere are likely to stabilise and then decline during this century.
Increase in sulphate aerosols over Asia
Depending on their size, concentration and vertical distribution, atmospheric aerosols (microscopic airborne particles such as smoke from forest fires, particles from volcanic eruptions, dust and pollutants) also have a heating or cooling effect on the atmosphere.
In the Northern Hemisphere, particularly over Asia, high sulphur emissions have had a cooling effect, which may have offset global warming due to increased greenhouse gases. Modelling studies conducted by CSIRO also indicate they may have contributed to the recent increases in rainfall observed over north-western Australia. Future levels of sulphur emissions in the Northern Hemisphere are uncertain.
Land-cover change
As numerous studies demonstrate, changes in land-use can alter the roughness and reflectivity of the earth’s surface and therefore the amount of radiation it absorbs, making them another agent of climate change. They may also alter the capacity of the land to absorb or produce greenhouse gases.
Further information
The scientific basis for climate change
See the summary for policy makers in the Working Group 1 Report, The Physical Science Basis on the website of the Intergovernmental Panel on Climate Change.
The Greenhouse Effect and Climate Change
See Greenhouse Effect and Climate Change (PDF, 5.5Mb)* on the Australian Bureau of Meteorology website.
*Requires Acrobat Reader
Last updated 7 March 2008.
