It is common knowledge that carbon dioxide contributes to climate change, but few people know exactly how. We believe that it is easier to motivate yourself to make a change when we understand more about our impact. In order to explain how carbon dioxide leads to global warming we need to understand the greenhouse effect.

**In short, the greenhouse effect is the reflecting of energy from the sun, back to Earth. This is caused by ‘greenhouse gases’ such as carbon dioxide, which are in the atmosphere of Earth. The temperature on Earth is rising because, in recent times, there has been a build up of these gases in the atmosphere.**

In this article I will explain how the natural greenhouse effect keeps the temperature on earth constant. Also, we will see that releasing more carbon dioxide can easily break this natural balance, leading to global warming.

#### How much energy does the earth get from the sun?

The sun releases 4×10^{26 }(4 with 26 zeros) joules of energy per second. By the time this gets to earth it has spread out, so for each meter squared at the earth, we get 1400 joules per second (watts).

If the earth absorbed all this energy, the temperature would be 123^{o}c. However, we must consider the **albedo** of the earth. Albedo is how much energy is reflected compared to the incoming energy. 35% of energy incident on the Earth is reflected, which means that the earth absorbs 910W per meter. However, this is per meter squared perpendicular to the sun, not per meter squared on the surface of the earth (see the diagram below). When we calculate per meter on the surface of the earth we get around 238W per meter.

#### How warm does this make the earth?

This energy warms the earth, and we can calculate the predicted temperature of the earth using the following equation:

where I is the intensity of energy (which we just calculated), and σ is Stefan-Boltzmann constant, which equals 5.67×10^{-8}. We can solve for T_{Earth} as shown below:

We can then convert kelvin to degrees, to get the predicted average temperature as -18^{o}c. This must be wrong, and this is because we are not considering the greenhouse effect.

#### What is the greenhouse effect?

The greenhouse effect is a natural effect which keeps the earth at a constant temperature. The energy emitted from the Earth is equal to the energy absorbed (meaning that the earth stays at a constant temperature). This means that the earth emits 238W. Gases in the atmosphere (such as carbon dioxide) reflect some of this energy back to earth. We now know that the intensity of energy to the Earth is actually the energy from the sun, added to the energy reflected in the atmosphere. To calculate the energy reflected by the atmosphere we can again use the equation

We can now calculate the intensity in the atmosphere by taking the temperature in the atmosphere to be around -30^{o}C and emissivity to be 0.8. The emissivity tells us how much energy is actually reflected. We get the intensity to be 152W. When you add this to the 238W from the sun, we can calculate the actual temperature of the earth.

#### Conclusion

This is the **natural **greenhouse effect, which keeps the Earth at a warm constant temperature. However, when humans release unnatural levels of carbon dioxide, we increase the emissivity of the atmosphere. This means we increase the amount of energy incident on the Earth, and this leads to an increase in the average temperature of the Earth. This is how global warming occurs, and this is the proof we need to show that carbon dioxide is directly linked to the temperature of the Earth. Increasing the temperature of the Earth has many significant impacts on the climate, and you can learn more about these here.

You can find out how much carbon dioxide you release, and learn about how to reduce it by using the Calculator on our website. If you want to learn more about climate change, visit our Discover page.

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