The Correlation between Temperature and Radiation – How it Affects our Planet

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We’ve all seen the video of Brian Cox holding up a graph to the climate change denier Malcolm Roberts, showing the rise in global temperature. Roberts claimed: ‘We’ve had a pause in this so-called warming for now 21 years.’ He later says ‘the data has been corrupted’ and ‘manipulated by NASA’.

If you missed that video then you can view it now below:

The climate change denier believes that there’s no ‘empirical evidence’, so let’s look at the physics of what’s happening to the Earth. To do this we have to understand the different ways energy is transferred. The Earth is constantly balancing energy through radiation, convection and conduction, but how does that affect us and how are we affecting it?

An understanding of heat transfer between land, water and the atmosphere will show how Earth’s energy balance works to regulate our climate.

To make it clearer we have to understand the difference between heat and temperature.

Energy is transferred from one substance or object to another, this process occurs when there’s a temperature difference between the two substances. This energy is heat and is always transferred from a warmer object to a cooler one. Earth’s surface absorbs and emits radiation at the same rate.

In measuring the average speed of atoms and molecules that make up a substance you get the temperature.

Radiation is how solar energy reaches Earth. When Earth absorbs the sun’s energy (most arrives in the form of visible light), the energy converts into heat. Some of that energy radiates away from Earth’s surface.

Because the atmosphere is heated from below, the temperature in the troposphere (lowest region of the atmosphere) decreases with height. Heat energy is also spread throughout Earth’s atmosphere through conduction and convection.

Conduction is the direct spread of heat from a warmer substance to a cooler substance. In this context the land or water is the warmer substance transferring to the cooler substance, which is the atmosphere. Conduction occurs on the Earth’s surface where the air is in direct contact with it. The heat energy transfers when molecules collide with one another.

In the lowest region of Earth’s atmosphere, the troposphere, heat is transferred vertically by convection. Convection is the spread of heat in a fluid, defined as gas or liquid where atoms and molecules are moving relatively freely.

So convection can occur in the atmosphere or in water. It forms when there is unequal heating of the atmosphere or water.

As the air or water warms and cools, it has an effect on density, creating a current of rising and sinking heat.

Conduction and convection work together to transfer heat. We can sense the resulting change in temperature, so these heat transfer mechanisms are known as sensible heating.

The Earth’s surface absorbs and emits radiation at the same rate, this balance in the rate of Earth’s absorption and emission occurs at -18°C, but Earth’s average temperature is actually much warmer.

This is because of the atmosphere: Earth’s atmosphere absorbs and emits infrared radiation, but it doesn’t absorb and emit equally.

Certain gases in the atmosphere absorb some radiation wavelengths (transferring their energy into heat), while other gases are transparent and allow radiation to pass through freely.

We must now consider the types of radiation entering Earth’s atmosphere.

The solar radiation the Earth receives primarily consists of shorter wavelengths of visible light. This incoming solar radiation may be scattered, reflected, or absorbed.

This is important as it contributes to the Earth’s energy balance between the incoming solar radiation and outgoing terrestrial radiation and if this isn’t balanced then the Earth’s temperature will change, this is what Brian Cox’s graph was indicating. This is basic physics and in a way, empirical.

In 1827, Joseph Fourier, a French mathematician and physicist, reasoned that there must be some type of balance of the incoming energy and the outgoing energy to maintain the Earth’s fairly constant temperature. His calculations indicated that the Earth should actually be much colder (-18°C).

To have an average temperature of 15°C, Fourier knew that there had to be another process occurring in the atmosphere, something similar to how a greenhouse retains heat.

 A greenhouse’s glass enclosure allows visible light to enter and be absorbed by the plants and soil. The plants and soil then emit the absorbed heat energy as infrared radiation. The glass of the greenhouse then absorbs that infrared radiation, emitting some of it back into the greenhouse and thus keeping the greenhouse warm even when the temperature outside is lower.

The sun’s visible wavelengths of radiation pass easily through the atmosphere and reach Earth. Approximately half is absorbed at Earth’s surface by the land, water, and vegetation. Some of this energy is emitted back from the Earth’s surface in the form of infrared radiation.

There are some gases, such as carbon dioxide, methane, and even clouds that absorb the longer wavelengths of outgoing infrared radiation from Earth’s surface. These gases then emit the infrared radiation, this creates a second source of radiation warming the Earth’s surface .This process is called the natural greenhouse effect and keeps Earth’s average global temperature at approximately 15°C.

If greenhouse gases increase, then more infrared radiation will be absorbed and emitted back toward Earth’s surface, creating an amplified greenhouse effect.

Relatively small changes in the amounts of greenhouse gases in Earth’s atmosphere can change the balance between incoming and outgoing radiation. Earth then warms or cools in order to restore the balance at the top of the atmosphere.

In a way it’s similar to the way Superman works: Superman gains all his powers from solar energy, thus giving him the ability to fly, heal quickly and burn through walls with his handsome glare. The difference is, climate change is real.

Cameron Sutherland

Cameron is a journalism and public relations student, powered by flat whites, George Orwell and a dash of Kanye West. 

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Last modified: 16th April 2018