Earth’s climate is rapidly changing, and not for the better! Average global temperatures have risen to approximately 1.1°C above pre-industrial levels, and the past decades have seen a series of record-breaking storms, droughts, floods, and fires around the world.
Our changing climate not only impacts wildlife, but also human society and wellbeing. In order to figure out how to tackle climate change, we need to first understand why it is happening.
Throughout its history, the Earth’s climate has been changing. However, the changes we are seeing now are happening at a much faster rate than they would do naturally. Why?
The cause is humans emitting carbon dioxide (CO₂) and other gases into the atmosphere. These gases impact on something known as the greenhouse effect.
The greenhouse effect involves certain gases in the atmosphere called greenhouse gases, which include CO₂. Adding more of these gases to the atmosphere heats up the planet.
What makes the Earth warm?
Energy from the sun is what makes the Earth warm. This energy is made of different types of radiation.
Radiation can take different forms. We see colour because of waves of visible light that bounce off the objects around us. But there are other kinds of radiation that we can’t see, like infrared radiation, and Ultra-Violet (UV) rays. Different types of radiation have different wavelengths, and together they make up the Electromagnetic Spectrum:
Unsurprisingly, the sun gives off visible light, which allows us to see. It also gives off UV and infrared radiation.
How does sunlight heat the Earth?
Actually, all three happen! A small percentage of radiation is absorbed by oxygen (O₂) and ozone (O₃) in the atmosphere, but most passes through and heads straight for the Earth’s surface.
Some of this radiation is then reflected (33%), but most (67%) is absorbed by the Earth’s surface and warms the planet up.
When we say the Earth “absorbs radiation”, we mean that it absorbs energy from the sun, and releases it again as infrared radiation.
Infrared radiation has a longer wavelength than visible light, so a lot of it is absorbed by the atmosphere (unlike the shortwave radiation from the sun).
Specifically, the infrared radiation is absorbed by gases called greenhouse gases that re-radiate the infrared waves out in all directions - some into space and some back to Earth.
The infrared radiation that is radiated back to Earth causes further warming at the surface and lower atmosphere. This extra warming is called the greenhouse effect.
There are several different greenhouse gases. These include:
water vapour (H₂O)
carbon dioxide (CO₂)
nitrous oxide (N₂O)
How are we making it worse?
The greenhouse effect is influenced by human activities, and this is what is causing the climate to change.
Without the greenhouse effect, the average temperature on the Earth would be -18°C! But too much of it is not good either:
Human activities are speeding up this process of global warming through increased production of greenhouse gases; especially carbon dioxide (CO₂).
This graph shows the historical CO₂ concentration in the atmosphere. It is easy to see that this has increased dramatically in the past 70 years .
We’ve also released plenty of methane and N₂O.
This means that more of the infrared radiation coming off of the Earth is re-radiated back towards the Earth’s surface, warming it up.
In the next chapter, we will look at the greenhouse gases in more detail and learn how to compare them. After that, we’ll look at where and why humans produce so much of them.