Glaciers are melting, sea levels are rising, cloud forests are drying, and wildlife is scrambling to keep pace. It's becoming clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than in the last 650,000 years.

We call the result global warming, but it is causing a set of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. As the Earth spins each day, the new heat swirls with it, picking up moisture over the oceans, rising here, settling there. It's changing the rhythms of climate that all living things have come to rely upon.

Greenhouse effect

The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse.

First, sunlight shines onto the Earth's surface, where it is absorbed and then radiates back into the atmosphere as heat. In the atmosphere, "greenhouse" gases trap some of this heat, and the rest escapes into space. The more greenhouse gases are in the atmosphere, the more heat gets trapped.

What causes global warming?

Deforestation: burning and removing vegetation

Plants take up carbon dioxide from the air during photosynthesis and are therefore often referred to as carbon 'sinks'. When land is cleared and vegetation removed or burnt, the stored carbon is converted back to carbon dioxide. Since 1788, we have cleared 20 billion trees and significantly modified more than 70% of Australia's native vegetation.

Industry
Many industrial processes such as cement and liquid natural gas production and coal mining produce or emit a variety of greenhouse gases.

Burning of fossil fuels. Most of Australia's greenhouse gas emissions come from the burning of fossil fuels for energy (eg. for electricity and transport). When oil, gas or coal burns, carbon contained within it combines with oxygen in the air to create carbon dioxide.

Farming
Animals, particularly sheep and cattle, produce large amounts of methane. Some fertilisers also release nitrous oxide, which is another greenhouse gas.

Waste breakdown
Carbon dioxide and methane is released during the decay of food, vegetation and paper dumped in landfills. The same thing occurs when sewage wastes break down.

Impacts of climate change

Climate change is one of the greatest social, economic and environmental challenges of our time. Human activity is causing the climate to change. This, in turn, is having an impact on Australia's rainfall, temperatures, bushfire frequency, health, heritage and biodiversity for current and future generations.
During the past 100 years, global average surface temperature increased by about 0.7°C. Since 1910 the average temperature of Australia has risen by about 1°C. Although these increases sound small, they have a big impact on the world's climate.

How will I be affected?

It is difficult to precisely predict what the impacts of climate change will be, as they vary with each region. Best estimates are that by 2030 Australia will face:

• - a further 1ºC of warming in temperatures
• 
  - up to 20 per cent more months of drought
• 
  - up to 25 per cent increase in days of very high or extreme fire danger
• 
  - increases in storm surges and severe weather events.

Australia is very vulnerable to the effects of climate change. We are already the driest inhabited continent on earth, heavily exposed to the dangers of extreme heat and drought. We are home to many globally important and vulnerable ecological systems. Australians are overwhelmingly coastal dwellers.

Our industries and urban centres face ongoing water limitations. Our economy, including food production and agriculture, is under threat. The longer we wait to act on climate change, the more it will cost and the worse its effects will be.

Climate change solutions

According to the best science, an average global warming of 2°C or more would result in dangerous climate change, leading to irreversible social, economic and environmental impacts.

We must act now to reduce greenhouse gas emissions. Delays will make the transition to reduced emissions increasingly expensive and difficult, with much greater risk of failure.

Other developed countries with large industrial sectors have reduced emissions since 1990 using a combination of energy efficiency, renewable and low-emission technologies and re-forestation. Norway has reduced emissions by 18%, Germany by 17% and the United Kingdom by 14%.

The good news is that Australia is well-placed to reduce emissions. We are a wealthy nation; we have plentiful renewable sources and access to world-class skills and technology.

Written by Bruno Romeiro de Oliveira (Biologist) and  Rodrigo B. Foschini (Environmental Engineer)