Some gases in the Earth’s atmosphere trap heat and stop it escaping into space. We call these ‘greenhouse gases‘. These gases act as a warming blanket around the Earth, known as the ‘greenhouse effect’.
Greenhouse gases come from both human and natural sources. Gases like carbon dioxide, methane, and nitrous oxide naturally occur in the atmosphere. Others, such as chlorofluorocarbons (CFCs), are only produced by human activity.
When short-wave radiation from the sun reaches Earth, most of it passes straight through and hits the surface. The Earth absorbs most of this radiation and gives off longer-wavelength infrared radiation.
The greenhouse gases absorb some of this infrared radiation, instead of it passing straight out into space. The atmosphere then emits radiation in all directions, sending some of it back to the surface, causing the planet to heat up. This process is known as the ‘greenhouse effect’.
The greenhouse effect is critical to our survival. In fact, without greenhouse gases, Earth would be about 30 degrees colder than it is today. Without greenhouse gases and their warming effect, we wouldn’t be able to survive.
However, since the Industrial Revolution, we’ve been adding more and more greenhouse gases into the air, trapping even more heat. Instead of keeping Earth at a warm, stable temperature, the greenhouse effect is heating the planet at a much faster rate. We call this the ‘enhanced greenhouse effect’ and it’s the main cause of climate change.
Human causes of climate change
Humans cause climate change by releasing carbon dioxide and other greenhouse gases into the air. Today, there is more carbon dioxide in the atmosphere than there ever has been in at least the past 2 million years. During the 20th and 21st century, the level of carbon dioxide rose by 40%.
We produce greenhouse gases in lots of different ways:
- Burning fossil fuels – Fossil fuels such as oil, gas, and coal contain carbon dioxide that has been ‘locked away’ in the ground for thousands of years. When we take these out of the land and burn them, we release the stored carbon dioxide into the air.
- Deforestation – Forests remove and store carbon dioxide from the atmosphere. Cutting them down means that carbon dioxide builds up quicker since there are no trees to absorb it. Not only that, trees release the carbon they stored when we burn them.
- Agriculture – Planting crops and rearing animals releases many different types of greenhouse gases into the air. For example, animals produce methane, which is 30 times more powerful than carbon dioxide as a greenhouse gas. The nitrous oxide used for fertilisers is ten times worse and is nearly 300 times more potent than carbon dioxide!
- Cement – Producing cement is another contributor to climate change, causing 2% of our entire carbon dioxide emissions.
Natural changes to the climate
The leading cause of climate change is human activity and the release of greenhouse gases. However, there are lots of natural causes that also lead to changes in the climate system.
Natural cycles can cause the climate to alternate between warming and cooling. There are also natural factors that force the climate to change, known as ‘forcings’. Even though these natural causes contribute to climate change, we know that they are not the primary cause, based on scientific evidence.