Lesson video

Hello, I'm Mrs. Adcock, and welcome to today's lesson on greenhouse gases.

We are going to look in today's lesson at what are greenhouse gases, what activities release greenhouse gases into the atmosphere, and how are greenhouse gases linked with the greenhouse effect.

Today's lesson outcome is, "I can explain the effect of greenhouse gases on the temperature of Earth's atmosphere." Here are some of the keywords that we will cover today in our lesson on greenhouse gases.

So the first keyword is greenhouse gas, infrared radiation, frequency and global warming.

Here you can see those keywords written in a sentence.

You might want to pause the video here and read through those statements.

Alternatively, you might want to pause and make a note of those so that you can refer back to them later on in the lesson if needed.

Today's lesson is split into four sections.

So the first part is on carbon dioxide, which is a greenhouse gas.

Then we're going to focus on methane, which is another greenhouse gas, before looking at the greenhouse effect.

And the final part of today's lesson will be on global warming.

So let's get started on looking at carbon dioxide.

Methane, water vapour and carbon dioxide are all greenhouse gases, and we can see there that the formula for methane is CH4.

The formula for water vapour is H2O, and the formula for carbon dioxide is CO2.

So they are all greenhouse gases.

And what is a greenhouse gas? Well, greenhouse gases are gases that absorb lower frequency infrared, so that IR means infrared, so they absorb lower frequency infrared radiation and trap heat energy in the atmosphere.

And infrared radiation is a type of electromagnetic radiation.

These gases exist naturally in the atmosphere.

So there's lots of talk about how humans have led, human activity has led to increased levels of greenhouse gases.

But methane, water vapour and carbon dioxide are all released by volcanoes, and they do exist naturally in our atmosphere.

We're gonna focus first on carbon dioxide.

So how has human activity increased the levels of carbon dioxide in the atmosphere? Hopefully you were able to think about the complete combustion of fuels.

So when fuels burn in a plentiful supply of oxygen, the products will be carbon dioxide and water.

So the complete combustion of fuels releases carbon dioxide into the atmosphere, and humans burn fossil fuels a lot.

So some examples of where humans combust fuels include in cars, we are combusting diesel and petrol, but not just cars, in lorries and other vehicles too.

To cook food, we combust fuels, and also to generate electricity.

And you might be able to think of some additional examples of where humans combust fuels.

And since humans have started combusting fossil fuels, the levels of carbon dioxide in the atmosphere have increased by 200 times.

Plants are great though because they are removing carbon dioxide from the atmosphere by photosynthesizing, and we can see there the equation for photosynthesis, and that is carbon dioxide, so taken from the atmosphere and water react together to produce glucose and oxygen.

However, humans are cutting down trees, so humans have reduced the amount of carbon dioxide being taken out the atmosphere by cutting down trees, and this is known as deforestation.

So less carbon dioxide is being taken out of the atmosphere, which again leads to increased levels of carbon dioxide in the atmosphere.

Right, time for a check.

Which of the following are greenhouse gases? A, water vapour.

B, carbon dioxide.

C, methane.

D, sulphur dioxide.

So well done if you chose A, B, and C.

So water vapour, carbon dioxide and methane are all greenhouse gases.

Water vapour is less of a problematic greenhouse gas because it can condense in the Earth's atmosphere.

However, carbon dioxide and methane remain in the gassier state.

Another question here, which of the following have led to an increase of carbon dioxide in the atmosphere? Is it A, deforestation.

B, complete combustion of fuels, or C, photosynthesis? You might want to choose more than one answer, so just consider whether each of those has led to an increase of carbon dioxide in the atmosphere.

The correct answer is deforestation and complete combustion of fuels.

So both of these have led to increased levels of carbon dioxide in the atmosphere.

Our first practise task is based on carbon dioxide, and you need to describe how deforestation leads to increased levels of carbon dioxide in the atmosphere.

And in your answer, you need to include the equation for photosynthesis.

So pause the video now, have a go at this question and then come back when you're ready to go over the answer.

Welcome back.

Your answer may include the following.

Trees photosynthesize, removing carbon dioxide from the atmosphere.

And the equation for photosynthesis is carbon dioxide and water react together to produce glucose plus oxygen.

So carbon dioxide is removed from the atmosphere and oxygen is released into the atmosphere.

When trees are cut down, less carbon dioxide is removed from the atmosphere, so the levels of carbon dioxide in the atmosphere will increase.

We have looked at carbon dioxide and how combustion of fuels and deforestation have led to increased levels of carbon dioxide in the atmosphere.

Now we're going to have a look at methane, which is another greenhouse gas.

Methane is a greenhouse gas, which is produced by microbes in the digestive system of cows.

And there we've got a picture of some cows, and humans farm cattle increasing the amount of methane gas released into the atmosphere.

So it's humans that have increased the number of cows on Earth, and therefore by farming cattle we are increasing the levels of methane gas released into the atmosphere.

So how can humans alter their behaviour to reduce methane released by cattle? You may have thought that we could reduce the amount of meat that we eat from cows.

This would reduce the need for so much cattle farming and therefore would reduce the amount of methane released into the atmosphere.

However, cattle farming is not the only type of farming that leads to increased levels of methane gas in the atmosphere.

Paddy fields are farmed to produce rice for human consumption.

So if we ate less meat and started eating more rice, this wouldn't just immediately solve the problem.

Paddy fields contain methane-emitting bacteria, which are a source of atmospheric methane gas.

Here we can see in the image a picture of a paddy field, and it's the bacteria which are contained in those paddy fields that release methane gas into the atmosphere.

Landfill sites are another source of methane gas, so bacteria which decompose organic matter release both methane and carbon dioxide into the atmosphere.

And we can see an image there of a landfill site.

So it's really important that we try to reduce the amount of litter and rubbish that's sent to landfill sites because this is another source of methane gas, which is a greenhouse gas.

Time for a check for understanding.

Which of the following have led to increased levels of methane in the atmosphere? Is it A, landfill sites? B, cattle? C, deforestation? Or D, rice paddy fields? The correct answer is landfill sites, cattle and rice paddy fields.

All three of those lead to increased levels of methane in the atmosphere.

Well done if you were able to identify all three of those answers.

Time for our second practise task of today's lesson.

So what you need to do here is identify who has correctly described why the percentage of greenhouse gases in the atmosphere is increasing.

And the second part of the task is to make changes to improve any incorrect comments.

Sofia says, "Deforestation has led to an increase of methane in the atmosphere." Laura says, "Landfill sites are ugly but have no impact on the level of greenhouse gases." Andeep says, "Cattle farming and paddy fields increase carbon dioxide gas in the atmosphere." And Lucas says, "Driving involves the combustion of fuels which produces carbon dioxide." So firstly, identify who is correct, and secondly, make improvements to any incorrect comments.

If you pause the video here, have a go at those two questions and then come back in a minute when you're ready to go over the answers.

Unfortunately, Lucas was the only person who correctly described how the percentage of greenhouse gases in the atmosphere has increased.

So he talked about the combustion of fuels producing carbon dioxide.

So well done, Lucas.

Sofia, Laura, and Andeep, hopefully you identified that their statements needed some improvements and you've made the following improvements.

"Deforestation has led to an increase of carbon dioxide in the atmosphere." "Landfill sites release carbon dioxide and methane as organic matter is decomposed." And to improve Andeep's statement, we've said that, "Cattle farming and paddy fields increase methane gas in the atmosphere." So well done if you are able to correct their incorrect comments.

Having already looked at carbon dioxide and methane, two greenhouse gases, we are now going to look at how these greenhouse gases lead to the greenhouse effect.

Here we have the sun, the Earth, and the layer of gas around the Earth is the atmosphere.

Those arrows coming from the sun represent high frequency infrared radiation.

So this is solar radiation coming from the sun down through our atmosphere to Earth.

High frequency and short wavelength infrared radiation is emitted by the sun.

It passes through the Earth's atmosphere and is absorbed at Earth's surface, and this warms the surface of the Earth.

When that infrared radiation reaches the Earth's surface, some of the infrared radiation is reflected back out to space.

So you can see it passes back out through the Earth's atmosphere and into space.

Some of the infrared radiation is absorbed at the Earth's surface and reradiated from Earth's surface at a lower frequency and a longer wavelength.

So we've shown that by using red arrows instead to show that this infrared radiation is now at a lower frequency and a longer wavelength.

And there's a label there showing that the red arrows represent infrared radiation at a lower frequency.

Most of this lower frequency and longer wavelength infrared radiation is absorbed by greenhouse gases and then it's radiated in all directions, warming the lower atmosphere.

And this natural phenomenon is known as the greenhouse effect.

Just to recap, we had high frequency infrared radiation emitted from the sun.

Some of it was reflected and passed back out to space, but some of it was absorbed at the Earth's surface and it was reradiated at a lower frequency and a longer wavelength.

And this lower frequency, longer wavelength infrared radiation is absorbed by greenhouse gases and then radiated in all directions, and this warms the lower atmosphere.

Let's check we've understood this.

What do greenhouse gases in the atmosphere do? A, absorb low frequency infrared radiation and radiate it in all directions? B, absorb high frequency infrared radiation and radiate it in all directions? C, allow high frequency infrared radiation from the sun to pass through Earth's atmosphere? D, absorb high frequency infrared radiation from the sun? So greenhouse gases absorb low frequency infrared radiation and radiate it in all directions.

They also allow the high frequency infrared radiation from the sun to pass through the Earth's atmosphere and reach the Earth's surface.

So well done if you chose A and C.

For our practise task on the greenhouse effect, you need to read the statements and decide if they are true or false.

And then the second part is to correct any false statements.

If you pause the video now and read through those statements, decide whether you think they are true or false, and then spend a moment correcting those false statements.

When you're ready, come back and we'll go over the answers.

Let's read through these together and decide if they are true or false.

"Infrared radiation is emitted from the sun." That statement is true.

Number two, "Greenhouse gases reduce the amount of higher frequency infrared radiation entering Earth's atmosphere from the sun." And that statement is false because greenhouse gases do not reduce the amount of higher frequency radiation entering the Earth's atmosphere from the sun.

Number three, "Ultraviolet radiation is absorbed by Earth and warms Earth's surface." Hopefully you identified that that is also false because it's not ultraviolet radiation, it is infrared radiation that's absorbed by Earth and warms the Earth's surface.

Number four, "Earth emits infrared radiation at a lower frequency than the infrared radiation it absorbed." That is true.

And number five, "Greenhouse gases reduce the amount of lower frequency infrared radiation that can escape from Earth's atmosphere." And that's also true because they absorb that lower frequency infrared radiation and radiate it back out in all directions.

Well done if you were able to correctly identify whether those statements were true or false, and hopefully you were able to correct those two false statements.

It is time for us to move on to the final part of today's lesson, which is on global warming.

So how does the greenhouse effect lead to global warming? Let's go and find out.

The greenhouse effect is a natural phenomenon.

If we had no greenhouse effect, then the infrared radiation would radiate from the Earth's surface straight back into space.

So there would be no greenhouse gases there to absorb any of the infrared radiation and it would all just pass straight back from the Earth's surface into space.

We don't want that to happen because infrared radiation transfers energy and we can feel infrared radiation as heat.

Without this heat Earth would be an icy wasteland with an average temperature of about -20 degrees Celsius.

Do you think that life could exist on Earth if we had no greenhouse effect? The short answer is no.

The greenhouse effect is essential to help maintain a stable temperature on Earth suitable for life.

We need some greenhouse gases in our atmosphere to absorb some of that lower frequency infrared radiation and radiate it out so that it warms the lower atmosphere.

But what if we increase the levels of greenhouse gases so that the rate energy is transferred into the Earth's atmosphere exceeds the rate it's transferred out.

So if we increase those levels of greenhouse gases so that they absorb more of the lower frequency infrared radiation, they radiate their radiation out towards the lower atmosphere and more energy is therefore kept inside the Earth's atmosphere rather than being transferred out into space.

What will happen then? Well, the Earth's average temperature will rise.

And an increasing average temperature of Earth's atmosphere is called global warming.

Why do we need some greenhouse gases in the atmosphere? A, they cause the greenhouse effect? B, they allow for a suitable temperature for life on Earth? Or C, they prevent heat being lost into space? We need some greenhouse gases in our atmosphere because they do cause the greenhouse effect, and that's a natural phenomenon that we need to occur.

Why do we need it to occur? Because that helps maintain a suitable temperature for life on Earth, and the greenhouse gases are preventing all the heat being lost back out into space.

Well done if you are able to identify that all three of those options are reasons why we need greenhouse gases in the atmosphere.

When will we have global warming, which is when the Earth's average temperatures rise? Will we have global warming if, A, the energy transferred into the atmosphere is greater than the rate it's transferred out? B, the energy transferred into the atmosphere is equal to the rate it's transferred out? Or C, if the energy transferred into the atmosphere is less than the rate it is transferred out? Just take a moment reading back over those three statements because they are very similar, so just identify the difference and see if you can work out which one is correct in explaining when we will have global warming.

Well done if you chose option A.

We will have global warming if the energy transferred into our atmosphere is greater than the rate at which energy is transferred out into space.

For the final practise task of today's lesson, you need to order these statements to explain how the greenhouse effect leads to global warming.

At the moment, these statements are not in the correct order, so you need to pop them into the correct order to explain how the greenhouse effect leads to global warming.

Read through the statements, have a go at completing that task and then come back when you are ready to go over the answers.

So the correct order for the statements should be, infrared radiation of higher frequencies from the sun passes through Earth's atmosphere.

The radiation is absorbed by Earth, warming Earth's surface and radiated from Earth's surface at a lower frequency.

Some of the low frequency infrared radiation is then absorbed by greenhouse gases and radiated towards Earth in all directions.

More greenhouse gases means more radiation is being emitted towards Earth than escaping to space.

This leads to an increase in Earth's average temperature known as global warming.

Well done if you correctly ordered those statements.

We have covered an awful lot in today's lesson, so well done.

We have reached the end of the lesson.

Let's just summarise the key points that we have covered in today's lesson.

Carbon dioxide and methane are common greenhouse gases.

Greenhouse gases reduce the amount of lower frequency infrared radiation that can escape from Earth's atmosphere.

Greenhouse gases do not reduce the amount of higher frequency infrared radiation that enters the atmosphere from the sun.

If the rate energy is transferred into the atmosphere exceeds the rate is transferred out, average temperatures rise.

An increasing average temperature of Earth's atmosphere is called global warming.

Well done, you have worked really hard in today's lesson.

I hope you've enjoyed it and I hope you're able to join me for another lesson soon.