Climate change

Global warming and ultimately climate change are issues of much discussion and debate throughout the world. While much progress in understanding the climate change issue has been made and some impacts of climate change are now inevitable, uncertainties continue to exist about aspects of the climate change science, and regarding societal developments that will affect the extent of future climate change and societal vulnerability.

What is the greenhouse effect?

The greenhouse effect is the term given to the natural process whereby energy originally from the sun (short wave radiation) is reflected from the Earth’s surface (long wave radiation) and trapped within the earth’s atmosphere by greenhouse gasses such as carbon dioxide, methane and water vapour. The trapping of this reflected energy within the Earth’s atmosphere results in the temperature conditions presently experienced at the Earth’s surface. However, this has not always been the case with the concentrations of key greenhouse gases, naturally fluctuating throughout the history of the earth resulting in far different climatic conditions than those experienced today, ranging from ices ages, to dramatically warmer periods when there were no ice-caps at all.

It is this increase in the concentration of the above mentioned gases, particularly carbon dioxide and methane, over the past 100-150 years (from human activities), which most scientists believe has resulted in an enhanced greenhouse effect. It is this enhanced or human induced greenhouse effect that is contributing to an average increase in global temperatures, leading to likely climatic changes in the future.

Greenhouse effect

Climate change – What does the latest data and information trends tell us?

Due to the far reaching, global issues and responses posed by the threat of a changing climate, a huge amount of research has been undertaken during recent years, culminating in a vast quantity of data and literature being made available by a variety of different sources. However, it is important to realise that some of this information is from reliable sources while some of it is not.

The information presented below is from a summary of the 2007 Fourth Assessment Report on Climate Change produced by an international panel of climate scientists, known as the IPCC (International Panel on Climate Change). This summary information is based on data collected up until the end of 2006 and therefore provides a reasonably up-to-date source of information, which has been peer reviewed by many of the leading scientific experts in climate change science. However, it is important to realise that climate change science is a very complex area of study, which scientists around the world are only just beginning to understand, and so it is advisable to read as much of the information available before drawing any firm conclusions about climate change and global warming.

Key finding of IPCC 2007 Fourth Assessment Report on Climate Change

Observed changes in climate and their effects

  • Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.
  • Eleven of the last twelve years (1995-2006) rank among the twelve warmest years in the instrumental record of global surface temperature (since 1850).
  • The temperature increase is widespread over the globe, and is greater at higher northern latitudes.
  • Land regions have warmed faster than the oceans.
  • Rising sea level is consistent with warming. Global average sea level has risen since 1961 at an average rate of 1.8 [1.3 to 2.3] mm/yr and since 1993 at 3.1 [2.4 to 3.8] mm/yr, with contributions from thermal expansion, melting glaciers and ice caps, and the polar ice sheets. Whether the faster rate for 1993 to 2003 reflects decadal variation or an increase in the longer-term trend is unclear.
  • Observed decreases in snow and ice extent are also consistent with warming. Satellite data since 1978 show that annual average Arctic sea ice extent has shrunk by 2.7 [2.1 to 3.3]% per decade, with larger decreases in summer of 7.4 [5.0 to 9.8]% per decade. Mountain glaciers and snow cover on average have declined in both hemispheres.
  • From 1900 to 2005, precipitation increased significantly in eastern parts of North and South America, northern Europe and northern and central Asia but declined in the Sahel, the Mediterranean, southern Africa and parts of southern Asia. Globally, the area affected by drought has likely increased since the 1970s.

Causes of change

  • Global greenhouse gas (GHG) emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004.
  • Global atmospheric concentrations of CO2, methane (CH4) and nitrous oxide (N2O) have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years.
  • Atmospheric concentrations of CO2 (379ppm) and CH4 (1774 ppb) in 2005 exceed by far the natural range over the last 650,000 years.
  • There is very high confidence that the net effect of human activities since 1750 has been one of warming.

Global projected climate change and its impacts

  • Continued GHG emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
  • For the next two decades a warming of about 0.2°C per decade is projected.
  • Based on a number of different scenarios, average global surface temperatures are expected to increase between 1.1°C and 6.4°C, while average sea level is expected rise between 0.18 and 059 metres by 2100.
  • Altered frequencies and intensities of extreme weather, together with sea level rise, are expected to have mostly adverse effects on natural and human systems.
  • To view the full report, visit the IPCC website: www.ipcc.ch. 

Climate change projections and impacts in Australia

Much of the research relating to climate change and its impacts in Australia has been conducted by the CSIRO. A brochure summarising climate change science and associated projections and impacts for Australia, indicates:

  • Global greenhouse gas (GHG) emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004.
  • The warming projected for Australia in 2070 is 1.0 to 2.5°C for a low emission scenario (similar to a 500 ppm CO2 equivalent path) and 2.2 to 5.0°C for a high emission scenario (similar to the world’s current path).
  • Warming is projected to be lower near the coast and in Tasmania and higher in central and north-western Australia. These changes will be felt through an increase in the number of hot days.
  • By 2030, southern Australia may receive up to 10% less rainfall while northern areas see changes of -10 to +5%. By 2050, southern areas may get 0 to 20% less rainfall, with changes of -20 to +10% in the north.
  • The frequency and extent of droughts is projected to increase over most of southern Australia.
  • There is greater than 90% likelihood that extreme fire weather will occur more often in southern Australia, with longer fire seasons.
  • Days with heavy rainfall are projected to become more intense over most areas in summer and autumn and in northern areas in winter and spring.
  • Tropical cyclone days are projected to increase in the north-east but decrease in the north-west, with the strongest cyclones becoming more intense.
  • The number of days with large hail is projected to increase along the east coast from Fraser Island to Tasmania and decrease along the southern coast of Australia.

More information is available from the CSIRO website at www.csiro.au/en/Research/OandA/Areas/Assessing-our-climate/Climate-change-science-and-solutions 

Other useful websites

Links to other useful sites with information and reports on climate change include: