1. Climate change

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Yes – The Earth's climate is changing. The global average surface temperature has increased since reliable measurements began in the late 1800s. During the past 100 years, global average surface temperature increased by about 0.7 °C. Global average temperatures are currently rising by 0.17 °C per decade. Scientists have also noticed that there has been an increase in heatwaves, fewer frosts, the retreat of glaciers and sea ice, and a rise in sea level of approximately 17 cm, during the 20th century.

Timeseries – Global climate variability and change

Global annual mean surface temperature anomaly (base 1961-90)

Source: Bureau of Meteorology, copyright Commonwealth of Australia, reproduced by permission

Are we causing climate change?

The Earth's atmosphere is very complex and there are many natural factors that influence climate. Scientists know that natural events such as volcanic eruptions and sunspots can change the Earth's climate. However most scientists now believe that in the last 50 years, greenhouse gas increases is the main cause of climate change.

The Intergovernmental Panel on Climate Change – an international body that assesses the latest science of climate change – stated that 'Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic [human produced] greenhouse gas concentrations' (IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S, D Qin, M Manning, Z Chen, M Marquis, KB Averyt, M Tignor and HL Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA).

Chapter 5 of the animation, Greenhouse describes the impact of human activities.

What is the greenhouse effect?

It's summer and you're at the beach. You get back to your locked car. You open the door and are hit by a blast of hot air.

The temperature inside a car left in the sun is much warmer than the outside air. This is an example of a greenhouse effect. The glass windows allow light energy from the sun to enter the car. This light energy hits things inside the car like the seats and carpet.

Some of the light energy is absorbed by the car's interior and changed to heat energy. The glass windows do not allow heat energy to pass out as easily as the light energy that came in, so some heat is trapped in the car. This causes the temperature inside the car to rise.

In many ways, this common experience is similar to what happens in our atmosphere.

The atmosphere is like a blanket of gases surrounding the Earth. Like the car's windows, the atmosphere allows light energy from the sun to pass through it easily. Some other types of energy from the sun like ultraviolet rays also get through but not as easily as sunlight.

When the light energy reaches the Earth's surface, much of it is absorbed and converted to heat energy. As the Earth's surface becomes hotter, some of the heat is released back into the atmosphere. Certain gases in the atmosphere trap some of this heat energy as it heads back into space. These heat-trapping gases are called greenhouse gases.

This process keeps the Earth – and us – warm. Our atmosphere and its delicate balance of gases have allowed our world, with its incredible diversity of life, to evolve.

In recent times however, people have been burning more fossil fuels, clearing more and more forests and increasing the amount of land used in farming. All these human activities are generating more and more greenhouse gases.

More greenhouse gases in the atmosphere means more escaping heat will be trapped – a bit like putting on an extra blanket on a cold night. Your body doesn't release any more heat. The extra blanket just prevents more heat from escaping, and so you get warmer.

The increase in greenhouse gases is called the 'enhanced greenhouse effect'. It's called 'enhanced' because, as more greenhouse gases are released into the atmosphere, more heat is trapped and the temperature of the Earth's surface and atmosphere will rise.

Scientists predict the rising temperatures are likely to affect people and other living things by a rising sea level and changes in weather patterns like drier, warmer winters and a greater chance of cyclones.

Watch the animation, Greenhouse, for an entertaining explanation of the greenhouse effect.

The enhanced greenhouse effect

To understand how the greenhouse effect works, we need to look at the properties of solar energy and what happens to this solar energy as it passes through the Earth's atmosphere.

Many different forms of the sun's energy reach the Earth. Visible light, or what we usually call sunlight, is the form of energy we are most familiar with. This itself is made up of a range of wavelengths of radiation, which can be seen when a rainbow forms, or a prism is used to split white light into the visible spectrum of colours. Red light, at one end of the colour spectrum, has a longer wavelength than other colours, while blue light has the shortest wavelength of visible light. Infrared (or heat) rays are nearest to the red part of visible light while ultraviolet (UV) rays (those that cause sunburn) are next to the blue part of visible light.

As solar energy passes through the stratosphere, a large amount of the ultraviolet radiation is absorbed by the ozone layer. Some gases in the atmosphere absorb some of the energy from radiation in the infrared portion of the spectrum. The major components of the atmosphere, nitrogen and oxygen, are almost completely transparent to the sun's rays, so most of the visible light will pass through the atmosphere.

The oceans, land, snow and ice absorb the remaining incoming solar radiation. As the solar energy is absorbed, it heats the surfaces it strikes. Any object that is hotter than its surroundings will lose heat. This heat energy is released back to space as infrared radiation. Some of this infrared radiation passes through the atmosphere on its way back into space.

Water vapour, carbon dioxide and the other greenhouse gases that are found in very small amounts in the atmosphere absorb some of the infrared radiation emitted by the Earth's surface. The absorbed radiation is not retained by the gas molecules but is re-emitted in all directions, thus increasing the temperature of the Earth's surface. This warming effect, long recognised as a major element of the climate system, is known as the greenhouse effect.

Without the clouds, water vapour, carbon dioxide and the other greenhouse gases in the atmosphere, this warming effect would not occur. Assuming that the amount of infrared radiation reflected back to space from the warmed Earth's surface was unchanged, the global surface temperature would average –18 °C rather than the present 15–16 °C.

Changes in the proportions of different gases present in the atmosphere can change the proportions of the different forms of energy from the sun, which are absorbed or pass through the atmosphere to reach the Earth. These changes in the gases of the atmosphere can also alter the amount of energy that is trapped as it is re-radiated from the Earth.

Scientists have measured the increased atmospheric concentrations of existing greenhouse gases (carbon dioxide, methane, nitrous oxide and ozone), as well as the presence of new greenhouse gases such as chlorofluorocarbons (CFCs). Most of these gases, once released into the atmosphere, persist for tens to hundreds of years, with an associated long-term impact on the background atmospheric levels.

Using an understanding of the processes that govern the climate system, and applying this knowledge in computer climate models, scientists consider that the presence of additional greenhouse gases will affect the radiation balance of the atmosphere and lead to a warming at the Earth's surface. This is now generally referred to as the 'enhanced greenhouse effect'.

The actual impact on global climate is likely to be complex and involve changes in atmospheric and oceanic circulations, accompanied by possible changes in sea level, daytime temperatures, rainfall and other climatic variables.

Global climate model (GCM) simulations provide predictions of the global impact of the enhanced greenhouse effect. Regional climate models (or 'downscaling' models) can now provide predictions for specific areas of the Earth. These predictions are very important as they will help us to plan how we use the land in future. For example, if rainfall patterns change in Australia then we may need to stop farming in certain areas and move our crops to other areas.

Computer models

Scientists can investigate climate change using computers. With programs called 'global climate models' they model the atmosphere and explore how greenhouse gas levels may change climates around the world.

The Bureau of Meteorology Research Centre (BMRC) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) are two organisations in Australia that have developed global climate models.

Climate models are simplified mathematical representations of the Earth's climate system. These models are continually being improved. One way to test their accuracy is to make predictions of past climate changes. The BMRC model, for example, was found to successfully reproduce the main features of the world climate that existed 6,000 years ago.

Temperature

Using the atmosphere models, scientists can predict the temperature changes that would occur if the level of carbon dioxide in the atmosphere doubled. In most areas of the world, there would be an increase in temperature of between one and two degrees.

Rainfall

The likely change in rainfall across the world is a very complex issue as shown by a model prepared by the Bureau of Meteorology Research Centre. Some parts of the world, particularly in the tropics, will experience higher rainfall, while others may receive less, resulting in long droughts. There may be more severe rain events causing more floods. Even locations receiving less rain could experience worse floods.

Changing weather patterns – what the future might hold

Increasing temperatures and changing weather patterns over the next 70 years might seem attractive – after all, winters will become milder and there will be fewer wet days in some areas. However, there are serious environmental implications that are likely to accompany such changes.

Using global models, atmospheric scientists at the CSIRO are predicting that inland Victoria and western New South Wales are likely to lose up to 20% of their crucial winter rainfall and that the average temperature will increase by 1.8 °C by the year 2070. Not only that, but what rainfall that does occur is likely to be in heavy storms, thus increasing soil erosion. This will have a dramatic impact on Australia's agriculture, as this area covers the Murray-Darling Basin, which accounts for around 40% of national food production.

Projected temperature changes for the Murray-Darling Basin by 2030 and 2070

Projected temperature changes for the Murray-Darling Basin by 2030 and 2070

Units are in °C

Source: © CSIRO Australia, www.csiro.au/science/ps1f2.html

For those of you who like to ski, there is every likelihood that Australian snowfields will slowly be reduced to the very tops of the highest mountains for a very short period during the winter months. Current resorts will need to invest in powerful snow-making facilities to maintain ski runs on lower slopes.

More importantly, climate change may result in higher rainfall over the oceans, and the melting of ice in the Arctic and Antarctic regions, leading to rising sea levels. CSIRO scientists have estimated that over the next 25 years, sea levels will rise 5–12 cm. Although this does not seem to be a large increase, such rises will threaten to overwhelm many areas of the world, including the low-lying islands in the Pacific and Indian Oceans, the coastal areas of the Netherlands, the Florida everglades, and Bangladesh – all areas that are heavily populated.

International response

Are we changing the world's climate? We know that the level of carbon dioxide in the atmosphere is rising. But what effect will this have? Over the past 30 years these questions have been hotly debated. At first only a few people considered them. By the 1980s, however, there was enough concern that a scientific report was prepared by a group called the Intergovernmental Panel on Climate Change (IPCC). This report was discussed at a conference held in Toronto, Canada in 1988. There, some countries, including Australia, agreed to try and reduce the levels of carbon dioxide emissions. Since then, regular international meetings and conferences have been held to determine what actions countries can take to reduce greenhouse gas emissions and so help slow climate change.

The Intergovernmental Panel on Climate Change

The Intergovernmental Panel on Climate Change is an international panel of scientists and researchers that provides advice on climate change to the international community. It is acknowledged by governments around the world, including the Australian Government, as the authoritative source of advice on climate change science. It was established by the World Meteorological Organisation and the United Nations Environment Program in 1988.

The role of the IPCC is to assess the scientific, technical and socioeconomic information relevant for the understanding of the risks of human-induced climate change.

The IPCC has completed four comprehensive assessment reports to date, in 1990, 1996, 2001 and 2007. These reports have been instrumental in developing an international response by providing a firm foundation on which to build climate policy.

United Nations Framework Convention on Climate Change

The United Nations Framework Convention on Climate Change (UNFCCC) provides the basis for global action 'to protect the climate system for present and future generations'. Negotiated between 1990 and 1992, the UNFCCC was adopted in May 1992 and opened for signatures a month later at the United Nations Conference on Environment and Development in Rio de Janeiro, Brazil.

Australia ratified the Convention in December 1992 – one of the first countries to do so. The Convention entered into force in 1994 after a requisite 50 countries had ratified it. There are now 186 parties to the UNFCCC – almost all of the members of the United Nations. Parties to the Convention have agreed to work towards achieving the Convention's ultimate aim of stabilising 'greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system' (Kyoto2 2007 summary).

Kyoto Protocol

At a meeting held in Kyoto in 1997, developed countries agreed to reduce greenhouse gases by at least 5% by the period 2008–2012 based on 1990 levels. The target covers the six greenhouse gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6).

To reduce emissions, countries agreed to:

  • introduce new technologies and practices to improve efficiencies in industry
  • establish greenhouse gas 'sinks' such as forest plantations which take carbon dioxide out of the atmosphere.

The protocol will take effect when enough countries with high greenhouse gas emissions sign the agreement.

Copenhagen

The United Nations Climate Change Conference from 7 to 18 December 2009 in Copenhagen produced an Accord. This accord is not binding on any nations and will not replace the Kyoto Protocol when it ends in 2012. While the Accord agrees that climate change issues must be addressed and we must keep the temperature increase to below two degrees, it does not set binding targets.

In Copenhagen, parties also agreed to continue the Bali Roadmap negotiations with the aim of concluding them at the Climate Change Conference in Mexico at the end of 2010.

Australia's response to climate change

Australia has actively participated in all of the major international conferences on climate change.

In 1992, the Council of Australian Governments endorsed the National Greenhouse Response Strategy, which was reviewed and released in November 1998 as the National Greenhouse Strategy. On 3 December 2007, the Prime Minister signed the instrument of ratification of the Kyoto Protocol, and on 11 March 2008, Australia's ratification came into effect.

Australia has set a renewable energy target of 20% by 2020. This means that by 2020, one-fifth of Australia's electricity will come from renewable sources such as wind, solar and geothermal power.

Australia will focus on:

  • reducing its greenhouse gas emissions
  • adapting to the impacts of climate change we cannot avoid
  • helping to shape a global solution with Australia's participation in negotiations for a post–2012 global framework under the United Nations Framework Convention on Climate Change, in particular:

    • working to help shape a post–2012 outcome in the lead up to the Copenhagen Conference of the Parties in December 2009
    • seeking support for Australia's approach in the post–2012 negotiations.

Some of the key priorities for 2009–10 have included:

  • implementing the carbon pollution reduction scheme and expanded national renewable energy target
  • implementing the National Greenhouse and Energy Reporting System and continuing development of the Greenhouse and Energy Reporting Office
  • contributing to the development of an effective global response to climate change and undertaking the analytical work to position Australia well in the lead up to the Copenhagen Conference of the Parties in 2009
  • investing in the analytical work required to build an effective adaptation framework for Australia
  • working collaboratively with the states and territories to deliver a more streamlined and effective national approach to climate change.

Government initiatives and programs

The Commonwealth Government has dozens of programs to assist homes, industry including farms, individuals and schools to tackle climate change. See www.climatechange.gov.au. Most of the programs aim to help us reduce greenhouse gases, while some help our neighbours in the Pacific region to do the same. They also address ways we need to adapt to climate change that is occurring now and into the future.

National Greenhouse Gas Inventory

Information on the sources of and trends in Australia's greenhouse gas emissions is made available through the National Greenhouse Gas Inventory (NGGI). The inventory is essentially a database of human-induced greenhouse gas emissions sources and sinks, which are categorised into six sectors: energy, land use change and forestry, agriculture, industrial processes, solvent and other product use, and waste.

The Inventory forms a baseline from which decision makers are able to identify trends and patterns in sectors, monitor response action, and develop projections of future greenhouse gas emissions.