The greenhouse effect

The greenhouse effect

Earth's natural greenhouse effect makes life possible. Our planet warms up when humans burn fossil fuels and clear forests, intensifying the natural greenhouse. This is because growing amounts of greenhouse gasses are trapped in the atmosphere creating an "enhanced greenhouse effect".

The greenhouse effect is explained by CSIRO in the following four Q&As:

How does the greenhouse effect work?

The greenhouse effect is a natural process. Sunlight passes through the atmosphere, warming the Earth's surface. In turn, the land and oceans release heat, or infrared radiation, into the atmosphere, balancing the incoming energy. Water vapour, carbon dioxide and some other naturally occurring greenhouse gases can absorb part of this radiation, allowing it to warm the lower atmosphere.

This absorption of heat, which keeps the surface of our planet warm enough to sustain us, is called the greenhouse effect. Without heat-trapping greenhouse gases, average global surface temperature would be -18°C rather than the current average of 15°C.

What is the enhanced greenhouse effect?

Since the industrial revolution and expansion of agriculture around 200 years ago, we have been raising the concentration of carbon dioxide gas in the global atmosphere. Levels of other greenhouse gases have also increased because of human activities.

Higher concentrations of greenhouse gases in the Earth's atmosphere will lead to increased trapping of infrared radiation. The lower atmosphere is likely to warm, changing weather and climate.

Thus, the enhanced greenhouse effect is additional to the natural greenhouse effect and is linked to human activity changing the make-up of the atmosphere. (The enhanced greenhouse effect is often referred to as global warming.)

Is greenhouse just a theory?

Yes and no! The way in which greenhouse gases affect climate is based on observations and scientific interpretations, as is the evidence that human activities have increased concentrations of greenhouse gases.

The way in which these increases will affect our future climate is, and can only be, the result of theoretical calculations.

However, there is unequivocal evidence that greenhouse gases are increasing in the atmosphere. Since the industrial revolution the level of carbon dioxide alone has risen from approximately 280 ppm (parts per million) to approximately 390 ppm. This will have an effect on the world's climate. What is not clear is the exact magnitude of that effect.

Isn't greenhouse warming just part of a natural cycle?

The greenhouse effect is a natural phenomenon, but the extra gases produced by human activity are making it stronger.

We are now adding to these gases faster than oceans and plants can absorb them - the greenhouse effect is being 'enhanced' by humans. There is strong evidence that recent changes are unprecedented and not due to natural causes.

When considering how climate will be affected, we need to be mindful that global warming due to the enhanced greenhouse effect will be in addition to the natural fluctuations of climate.