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The science of climate change
What is climate change?
The greenhouse gases in our atmosphere help make the planet a warm and habitable place. They act like the outside covering of a greenhouse, trapping heat from the sun.
Greenhouse gases – such as carbon dioxide, methane and nitrous oxide – are emitted naturally from trees and animals, as well as from human activity.
An increase in human activities like driving cars, farming, burning coal, and cutting down trees, is in turn increasing the greenhouse gases emitted into the atmosphere each year.
These gases are trapping even more heat, causing the planet to warm up and our natural weather patterns to change.
This process is often called ‘global warming’ but it is better to think of it as ‘climate change’ because it is likely to bring about more extreme events – floods, storms, cyclones, droughts and landslips – rather than an increase in temperature alone.
Every country will be affected differently but the one constant is a changing climate.
Natural climate changes in Earth's history
The planet Earth has gone through massive changes in its 4.5 billion-year history. Its climate has naturally fluctuated between being very cold and covered in ice, or very hot.
In the past 10,000 years the planet’s climate has become much more stable, leading to flourishing flora and fauna, and the subsequent population explosion of humankind.
Despite this relative stability, scientists are now detecting changes which suggest the climate is becoming hotter on average, and more variable.
This variability is being attributed in part to increased levels of carbon dioxide in the Earth’s atmosphere. According to scientific studies, in the past 400,000 years the planet has never had so much carbon dioxide in its atmosphere as it does today, and the levels are continuing to rise[CDIAC data center. Petite et al., Nature 399: 429-436].
Further increases in carbon dioxide levels will continue to heat up the planet and change the climate. These changes could even be irreversible.
Let's take a look at the Earth
Our changing planet
The effects of a warming planet and disrupted climate patterns are already becoming evident.
Meteorologists are seeing an increase in the severity of storms, rainfall, droughts and floods around the world.
Eleven of the last twelve years have been the warmest on record.
In the Artic, sea ice is showing worrying signs of increased melting, and, further south in countries like Peru and Greenland, many glaciers have retreated significantly in the past few decades.
Antarctica, too, is showing similar impacts. The Larsen B ice sheet on the eastern side of the Antarctic Peninsula is breaking up, leading to increasing glacier flows of ice into the sea.
If these processes continue, sea levels will rise and inundate many low-lying regions of the world, including Florida, Bangladesh, and the Pacific Islands. This could have a devastating flow-on effect to all parts of the world.
The Intergovernmental Panel on Climate Change (IPCC) – an international body of independent climate change scientists and researchers – predict that this kind of sea level rise could happen within this century[Intergovernmental Panel on Climate Change. Climate Change 2001: Working Group I: The Scientific Basis] if action is not taken to reduce emissions.
Droughts and resulting water shortages are causing problems in warmer countries. In Australia, drought has had severe impacts on the whole country. Twenty-seven areas within Australia were declared areas of “exceptional circumstance” for drought in July 2006.
Farmers – who rely heavily on the availability of water – were particularly hard hit, with the government offering farmers social and financial assistance.
In New Zealand, scientists cannot yet say whether the extreme storms and flooding that have occurred in some regions are a direct result of climate change – but they do say it highlights how climate change might affect us.
It was once believed that climate change would happen far off in the future, to our grandchildren, or their grandchildren. However, the rate of change means we are at risk in our lifetimes.
This is a cause for action. We can still avert the more catastrophic impacts of climate change. Taking action now is like taking out an insurance policy for our future.
Complex climate systems
Earth’s climate systems are very complex but we do know the world will get warmer as more and more greenhouse gases are pumped into the atmosphere. How much we reduce our emissions globally will influence the level of temperature rise we can expect.
Climate scientists project that the Earth’s average temperature will increase by between 1.1 and 6.4°C. This might not seem like much but even a 1 to 2°C increase can have a big impact. For example, a temperature increase like this could lead to less frosts, reducing the ability of kiwifruit to be grown in some areas, or, in Australia, it would bleach 81 percent of the Great Barrier Reef.[CSIRO Marine and Atmospheric Research (Preston, BL and Jones, RN). 2006. Climate Change Impacts on Australia and the Benefits of Early Action to Reduce Global Greenhouse Gas Emissions]
Can we stop climate change?
Despite any measures we take to reduce greenhouse gas emissions now, the levels of carbon dioxide already in the atmosphere are expected to continue to affect and change the climate over our lifetimes.
However, if we act now and work together to reduce our emissions, the catastrophic effects of climate change may be avoided. We should also put in place plans to prepare for climate change and adapt to its impacts.
