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“Global warming is a greater risk to humanity than the war on terror, particularly in Australia where the stakes are high”: Al Gore.
Climate change
Ten years ago we weren't sure about climate change, but the latest United Nations International Panel on Climate Change (IPCC) Assessment Report, released in February 2007 says that the 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 mean sea level.
Today, pointers to the future of life on Earth are both unmistakable and locally significant. Countries around the world are seeing disappearing glaciers and thawing permafrost (the permanently frozen soils in countries near the poles), more intense tropical cyclones and floods, forest fires and extreme heatwaves.
The Earth has warmed, on average, by about 0.7 degrees C since 1906, with eleven of the twelve warmest years on record occurring in the past twelve years. There has been an increase in heatwaves, fewer frosts, and a warming of the lower atmosphere and oceans to depths of 3000m.
Australia will be significantly affected: our temperatures have increased by almost 0.9 degrees C since 1910, which is slightly more than the global average.
Our understanding of the role of humans in the observed changes in climate has improved markedly over the past couple of decades. The IPCC's Fourth Assessment Report states that most of the observed warming since the mid-20th century is very likely (greater than 90 per cent probability) due to the observed increase in human-created greenhouse gas concentrations in the atmosphere. And global warming appears to have accelerated during the past 30 years, this at a time when natural influences such as solar flares and volcanic eruptions (both of which cause changes in the atmosphere that reflect sunlight) should have reduced global temperatures.
Living in a greenhouse
People are changing the natural climate pattern by burning huge amounts of fossil fuels (coal, oil and natural gas), releasing billions of tonnes of carbon dioxide (CO2) into the atmosphere every year. This process began centuries ago, but has increased sharply in the last two centuries of industrial development.
Greenhouse gases are a natural part of the atmosphere. They absorb and re-radiate the sun's warmth, and maintain the Earth's surface temperature at a level necessary to support life.
The problem we now face is that human actions particularly burning fossil fuels, agriculture and land clearing are increasing the concentrations of the gases that trap heat within the atmosphere. This is the enhanced greenhouse effect, which is contributing to a warming of the Earth's surface.
Water vapour is the most abundant greenhouse gas. Its concentration is highly variable and human activities have little direct impact on its amount in the atmosphere. Humans have most impact on carbon dioxide, methane and nitrous oxide. Various artificial chemicals such as halocarbons also make a small contribution to the enhanced greenhouse effect.
Depending on our efforts to reduce emissions in the future, global average temperatures are projected to increase by between 2 and 5 degrees C by the end of this century, which could melt sea ice at the poles, raise ocean levels, flooding coastal towns and cities, alter local climate patterns, and change vegetation.
Effects on people and global economies that depend entirely upon our environment will be diverse and unpredictable. Disease risk is expected to change. Some crops may grow faster while others will be lost to drought. Not everywhere will have less water. Dwindling water supplies could cause conflicts in many regions, and rising sea levels are expected to create a large number of environmental refugees.
As natural ecosystems such as coral reefs are affected, biodiversity is likely to be reduced. Some species may struggle to adapt and survive, and others will change in response to warming and changing climatic conditions.
In the last 200 years, the oceans have absorbed around half of the carbon dioxide we produced. Research suggests that the ocean's ability to absorb ever-increasing levels of the gas could now be stretched to the limit. Land-use changes cause both release (through reforestation) and uptake (through plant growth) of carbon dioxide.
What can we do?
In the view of the IPCC, the world needs to quickly become energy-efficient and develop non-carbon-producing sources of energy, such as wind, solar, tidal, wave and geothermal. There is renewed and polarised debate about nuclear power as a substitute for traditional energy sources such as coal and gas.
The bottom line is that it is estimated that we will need to cut carbon dioxide emissions by 70 per cent by 2050 to stabilise atmospheric carbon dioxide concentrations at a level to avoid dangerous amounts of climate change.
How we do that involves every one of us, and begins with actions as simple as switching to low-energy light bulbs, reducing fuel use and turning the air conditioner thermostat up a degree or two. By reducing demand from power generators or energy sources that emit greenhouse gasses, we all play a part in reducing the problem.
