A Case For Change

The Age

Monday March 17, 2008

Ben Haywood

It is the greatest environmental threat to our planet, but why is the climate changing?: Ben Haywood gives a quick overview of a hot issue.

CLIMATE CHANGE is a natural process. Just as the weather changes from day to day, the climate changes over decades, centuries and millennia. But recently, the changes have become more dramatic.

A global warming is under way.

Scientists believe the world has warmed more rapidly in the past 100 years than ever before, and if it doesn't stop, the consequences will be dire.

The Bureau of Meteorology says the world is experiencing rapid climate change. In Australia, temperatures have risen, on average, by 1 degree since the 1950s. There have been more heatwaves and fewer cold days and frosts.

According to the Intergovernmental Panel on Climate Change, average world temperatures are likely to be between 1.4 degrees and 5.8 degrees higher by 2100 than they were in 1990.

It doesn't sound like much, but the Earth's ecology is fragile and even minor changes can have a big effect.

The IPCC warns that if global warming goes unchecked, 70 per cent of plant and animal species could face extinction. They predict hunger and disease will spread, and water resources will be further strained.

Scientists also expect an increase in the frequency and duration of extreme weather events such as heavy rains, storms, droughts and floods.

Sea levels will also rise.

As the Earth's atmosphere warms, so do the upper layers of oceans. As water heats, it expands, causing the sea level to rise, threatening low lying coastal areas.

Why is this happening?

Scientists think we're causing these climate changes ourselves.

Our planet is like a giant greenhouse. The gases in our atmosphere work to trap the sun's heat and keep the Earth warm.

Too little of these gases and the planet would freeze. Too much, and we overheat.

Human activity - mostly the burning of fossil fuels (which produce greenhouse gases), intensive agriculture and land clearing (reducing the Earth's capacity to absorb carbon dioxide) - is causing an increase in the greenhouse gas in the atmosphere, creating an enhanced greenhouse effect.

The atmosphere's carbon dioxide (a key greenhouse gas) levels are higher now than they have been at any other point in the past 420,000 years - and our carbon emissions are still growing.

A report last month from the Federal Government's chief advisor on climate change, Ross Garnaut, revealed emissions have grown faster in the early 21st century. Emissions grew at 1.1% per year from 1990 to 1999. From 2000 to 2006, they grew at 3.1% per year.

In his report, Professor Garnaut said that for a 50-50 chance of limiting global temperature rises to two degrees, greenhouse gas emissions would need to peak in just two years, and drop to less than half of 2000 levels by 2050.

As part of the global effort, he said Australia would need to cut emissions by 90% by 2050 to avert the worst effects of climate change.

The Federal Government's current target is to reduce emissions by 60% by 2050.

NEED TO KNOW

WEATHER

The weather is what it is like outside, right now. It changes from moment to moment and place to place, sometimes very rapidly. It is the temperature and the humidity, the wind and rain, and everything in between.

CLIMATE

The climate is based on long term averages in the weather. Although there might be a cold day in summer, the climate is what tells us that winter is usually cold. But climate is not static. Just like the weather, it changes too - but over much longer timeframes. Decades of climate data allow us to examine these subtle changes, and make predictions about how the climate will be different in future.

THE GREENHOUSE EFFECT

The greenhouse effect is a natural process that is vital to the survival of life on Earth. Without it, the average global surface temperature would be minus 18 degrees. So, how does it work?

First, light from the sun passes through the atmosphere and warms the Earth's surface. The land and oceans then release this heat as infrared radiation.

Naturally occurring greenhouse gases, such as water vapour and carbon dioxide, absorb some of this energy, warming the lower atmosphere.

Because the amount of greenhouse gases in the atmosphere is increasing, more of this energy is being absorbed, making it hotter.

This is known as the enhanced greenhouse effect.

FOSSIL FUELS

About 80 per cent of the world's energy comes from burning greenhouse gas producing fossil fuels such as natural gas, oil and coal.

It is estimated that of the billions of tonnes of carbon dioxide produced by burning fossil fuels each year, only half is absorbed by natural processes. The rest builds up the atmosphere, enhancing the greenhouse effect.

AUSTRALIAN EMISSIONS

Australia is one of the biggest emitters of greenhouse gases per capita in the world. For every person, Australia emits about 27 tonnes of greenhouse gases a year.

In 2005, Victoria's greenhouse gas emissions alone were higher than some entire countries, including Austria, Hungary, Sweden and Switzerland. This is largely due to the state's reliance on brown coal, which produces high levels of greenhouse gas, for electricity generation.

More than 50% of Victoria's emissions come from coal-fired power stations that produce 90% of the state's electricity.

SOURCE: climatechange.vic.gov.au

© 2008 The Age

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