Lesson video

This lesson is called Greenhouse Gases and global warming, and is from the unit Climate change and greenhouse gases.

Hi there, my name's Mrs. McCready and I'm here to guide you through today's lesson.

So thank you very much for joining me today.

In our lesson today, we're going to describe what greenhouse gases are and be able to list them, and we're going to see the effects of adding more greenhouse gases into the atmosphere.

In our lesson today, we're gonna come across a number of keywords and they're listed up here on the screen for you now.

You may wish to pause the video to make a note of them, but I will introduce them to you as we come across them.

So in our lesson today, we're going to first of all have a look at what the natural greenhouse effect is before we consider what greenhouse gases are, and then how we might be able to reduce greenhouse gases.

So are you ready to go? I certainly am.

So let's get started.

Now we know that Earth supports life.

And as far as we are aware, Earth is the only planet in our solar system that supports life.

We are also only aware of Earth supporting life in anywhere else in the universe, but that's very unlikely that we are the only place.

However, it is still the only place that we know of that supports life, and that makes planet Earth extremely special.

Now, the average temperature of Earth is a nice, warm plus 14 degrees.

And at that temperature, it is warm enough for lots of plants and animals to survive and thrive.

And we see that across the Earth, this abundance of life in many, many places.

Now, the reason Earth is at this lovely, warm 14 degrees on average is due to a natural process called the greenhouse effect.

So the greenhouse effect is a natural process that helps to keep the Earth at this lovely, warm temperature.

If the greenhouse effect didn't happen, then the Earth would actually be a really chilly on average minus 20, which is just colder than your freezer.

And if that was the average temperature across the surface of the Earth, then it would be far too cold to support the wide range of life that exists on Earth.

Most of the planet would be really very cold and deeply frozen.

And life, if it did exist, would be very hard indeed.

So the greenhouse effect helps to keep the Earth at a nice warm temperature, warm enough for this abundance of life to exist and flourish on Earth.

So without the greenhouse effect, what would be the average surface temperature of Earth? Plus 20 degrees, plus 14 degrees, minus 14 degrees or minus 20 degrees? I'll give you five seconds to decide.

So you should have said that the average surface temperature without the greenhouse effect on Earth would be minus 20 degrees.

Very cold indeed.

So the greenhouse effect is caused by some of the gases in the Earth's atmosphere.

So let's look at what the atmosphere is.

So most of the atmosphere is contained within the first seven to 15 kilometres above the surface of the Earth.

80% of the atmosphere is found in that section.

And in our diagram on the screen, we have to draw that as a really thin line around the surface of the Earth to keep it in scale.

The atmosphere does extend much further than that, out into space.

And you can see that that is also a very thick layer, but a very thin atmosphere.

So only 20% of all the gas contained in the atmosphere is contained in this very outer section.

Most of it is contained very close to the surface of the Earth.

Now the atmosphere is a mixture of a number of different gases, all sitting alongside each other.

Now, about 78% of it is nitrogen and another 21% of the atmosphere is oxygen.

So the vast majority of the atmosphere is made up of nitrogen and oxygen with the rest being made up of carbon dioxide, but only 0.

04% is carbon dioxide, and the rest is a mixture of other gases, including methane and water vapour.

Now, carbon dioxide, methane and water vapour are all known as greenhouse gases.

So what are greenhouse gases and what is the greenhouse effect that they cause? Well, the greenhouse effect starts with the Sun.

So the Sun warms the Earth and the Earth's atmosphere, and the greenhouse gases are present within the atmosphere.

And what they do is trap some of the heat in the atmosphere and stop it from radiating out into space.

And because they trap some of the heat in the atmosphere, they make the atmosphere warmer than it would be if the greenhouse gases were not in the atmosphere.

And this means that the surface of the Earth gets warmer.

So the Earth's surface temperature is warmer because more heat is trapped within the atmosphere by the greenhouse gases.

And this process is known as the greenhouse effect.

And this is a natural process which has been going on for many millions, if not billions of years on the surface of the Earth and in the atmosphere and has helped to keep Earth at a temperature that is just right for life.

So water vapour is a greenhouse gas, true or false? So you should have said that that is true.

And it's true because water vapour is an invisible greenhouse gas in the atmosphere that we cannot see.

And clouds are made of tiny droplets of water in the liquid state, whereas water vapour is water in the gaseous state.

Well done if you knew all of that.

So let's review that so far.

So we've got Sam, Jun, and Laura, and they are discussing the greenhouse effect.

Sam says, "Earth's atmosphere is heated by greenhouse gases." Laura comments that "Greenhouse gases make it easier for the Sun to heat the Earth's atmosphere." And Jun says, "Greenhouse gases make a protective shell around the Earth." But who is correct? And what would you say to help the ones who have got it incorrect understand more clearly? So pause the video and come back to me when you are ready.

Okay, let's review Sam, Jun, and Laura, plus your work.

So who is correct and how would you help the ones who were incorrect understand more clearly? Well, Sam is incorrect that the Earth's atmosphere is heated by greenhouse gases, because the atmosphere is not heated by the gases, the gases are heated by the Sun, or by the warmth of the Earth, which has come from the Sun and is being reflected back into the atmosphere.

Now, Laura is correct that greenhouse gases make it easier for the Sun or the warm Earth to heat the Earth's atmosphere.

And Jun is incorrect that greenhouse gases make a protective shell around the Earth, but they are spread throughout the atmosphere but not as a protective shell.

So well done if you've made those corrections.

Okay, let's move on to have a look at the greenhouse gases.

So increasing the amount of greenhouse gases in the atmosphere will enhance the greenhouse effect because there will be more greenhouse gases to trap heat in the atmosphere and stop it from escaping into space.

Now if we look at a graph about greenhouse gas emissions from burning fossil fuels from 1750 to the present day, you can see how since the start of the industrial revolution and from about 1850 onwards, human activity has added billions of tonnes of greenhouse gases into the Earth's atmosphere.

And you can see how it started to increase relatively slowly at first and has increased faster and faster since, well, at least 1950, after the Second World War.

Now the amount of greenhouse gases in the atmosphere directly relates to how much global warming happens.

And as we increase the amount of greenhouse gases in the atmosphere, we trap more and more heat in the atmosphere and this increases the amount of global warming that occurs.

Now, global warming is the way we describe how the Earth is heating beyond what it should be.

So if we look at a graph showing the average temperature over the course of the last 2000 years, you can see that, on average, the temperature is about 13 degrees plus or minus 0.

3 degrees.

And if we draw a dashed line through that, just over 13 degrees is the average global temperature for the vast majority of the last 2000 years.

But since the industrial revolution, global warming has started and that is because the amount of greenhouse gases being put into the atmosphere has trapped more heat in the atmosphere, driving global warming.

And you can see that in the last 100 years or so, this really sharp peak of increase in average surface temperature on the graph, and that is global warming, not the fact that the greenhouse gases are warming the Earth naturally, but global warming is this extra warming that is happening because of the extra greenhouse gases in the atmosphere.

Now, 99% of climate scientists, virtually all climate scientists agree that global warming is caused by increased amounts of carbon dioxide in the atmosphere.

And that level of greenhouse gases in the atmosphere, the quantity in the atmosphere has increased because of the activities that humans have been undertaking.

So it hasn't happened because of something that is naturally occurring on Earth that would've happened anyway regardless of us.

But it is happening because of our activities, the things that we are doing and the choices we are making is driving the amount of greenhouse gases into the atmosphere and also therefore driving global warming.

So how sure are climate scientists that human activity is causing global warming? They think it is definitely the cause, they think it may be the cause, or they do not think it is the cause? I'll give you five seconds to decide.

Okay, so you should have chosen A, that climate scientists definitely think human activity is causing global warming.

Well done if you chose that option.

Now more than half of the natural greenhouse effect is caused by water vapour in the atmosphere.

So let's have a quick look at the water cycle.

So water is present in rivers and lakes and in the ocean and seas.

And water evaporates from these large pools of water into the atmosphere and then condenses to form clouds.

And when the water is condensed enough into large droplets in the clouds, it can then fall as precipitation.

So rain, sleet, snow, hail.

And when it falls as precipitation, it lands on the land and then runs off into the rivers and the lakes which drain into the seas, and the process starts again.

So this is the water cycle.

Now, when water is present in the atmosphere as water vapour, it is invisible because it is in the gas state.

We can't see it when it is in that state.

But when it condenses into its liquid form, we can see it in the form of clouds.

So clouds are liquid water, not gaseous water.

And because they're in the liquid form, we can see them 'cause they show up white.

Now water is made when fuels are burnt.

So when we are burning wood or coal, oil or gas, we are releasing water into the atmosphere as one of the greenhouse gases that are emitted as part of the burning process.

And you can see that water in the smoke that is being emitted from the chimneys of a power station.

Because it's the water droplets in the smoke that make the smoke visible, give it that kind of dirty, cloudy look.

So when we are burning fuels, we are adding water into the atmosphere in the form of water vapour.

And what happens is that because there's more water in the atmosphere, more rain can fall.

Because the total amount of water present in the atmosphere doesn't overall change.

It's just moving from one state to another.

So it evaporates into the atmosphere as water vapour, condenses into clouds and then falls as precipitation.

So if we're adding more water vapour into the atmosphere and the total amount of water vapour in the atmosphere doesn't change, then more water must fall from the atmosphere as precipitation.

And so by burning fuels and releasing water into the atmosphere, what we're doing is increasing the amount of rain that will fall.

Water vapour in the atmosphere is one cause of global warming, true or false? So you should have said that that is false.

And that is false because water vapour is a greenhouse gas and it is the main cause of the natural greenhouse effect, but it is not causing the temperature of the Earth to increase further, because human activity does not directly increase the amount of water vapour in the atmosphere, because as much water we add in comes back out again as precipitation.

But well done if you understood that.

Now water vapour is one of several greenhouse gases, and carbon dioxide and methane are also greenhouse gases in the atmosphere.

And carbon dioxide and methane are the main causes of the greenhouse effect.

So carbon dioxide is CO2, so one carbon and two oxygen atoms. And methane is CH4, so one carbon and four hydrogen atoms all bonded together.

So this is carbon dioxide and methane.

And these are the main causes of the greenhouse effect.

Now, carbon dioxide is also produced when fuels are burnt just like water vapour is.

And when we burn fuels, we are burning them for a number of different purposes.

We might burn them to generate electricity in power stations or we might burn them to heat our homes, like in our hot water boiler for instance.

Or we might burn them to transport us around.

So as petrol, diesel or aviation fuel in cars and lorries and trains and planes, for instance.

So these are all examples of when we are burning fossil fuels: to move us around, to heat up our homes and to provide us with electricity, are all examples of when we do that.

And therefore these are all examples of different types of human activity that adds carbon dioxide into the atmosphere.

And by doing so, we are enhancing the greenhouse effect.

So by increasing the levels of carbon dioxide in the atmosphere, we are enhancing the greenhouse effect.

And this is a cause of global warming.

Methane is also released into the atmosphere, but through a different set of processes, generated through industry and agriculture.

So methane is released when we make things like paints, fertilisers, things like that.

The industrial processes required to make these substances release methane into the atmosphere.

Farming also releases methane into the atmosphere, particularly when we are farming cattle because cows produce a lot of methane because of the digestive processes that they have in order to turn grass into nutrition for their own body.

Methane is also released through the decomposition, so the breakdown of waste in landfill sites.

So all of these processes are producing methane.

These are all examples of human activities and they're all driving the quantity of methane gas in the atmosphere.

And this is another cause of global warming.

So human activity is increasing the amount of which gases in the atmosphere? Carbon dioxide, methane, oxygen, and water vapour.

What do you think? So you should have chosen carbon dioxide and methane.

Well done if you did.

So let's just summarise that part of the lesson on greenhouse gases.

So we know that water vapour is water in the gas state and it is invisible.

It's found in the atmosphere, but we can't see it.

So what do you think about each of these statements about water vapour? Are you sure it's correct? Do you think it's correct? Do you think it's incorrect or are you sure it is incorrect? Statement A is water vapour is a greenhouse gas.

Statement B is human activity increases levels of water vapour in the atmosphere.

And statement C is water vapour is one cause of global warming.

So pause the video and come back to me when you are ready.

Okay, let's review your answers.

So water vapour is a greenhouse gas.

That is true.

Human activity increases levels of water vapour in the atmosphere is wrong.

It doesn't, the quantity of water vapour in the atmosphere remains about the same.

And water vapour is one cause of global warming is also incorrect.

Did you get all three answers right? Well done if you did.

Okay, let's move on to the last section of our lesson now, which is about how we might reduce the amount of greenhouse gases in the atmosphere.

So the greatest cause of global warming is the increasing levels of carbon dioxide in the atmosphere.

About three quarters of the carbon dioxide emissions are from burning fossil fuels.

This is used to generate electricity, to provide heating and used for transport.

So all of these activities are adding increasing quantities of carbon dioxide into the atmosphere.

And this is driving global warming.

But we can switch to renewable energy resources for some of these processes at least.

For generating electricity, it's straightforward enough.

Instead of burning fossil fuels, to use renewable sources such as wind turbines, solar panels, and wave technology in order to generate electricity through renewable sources, rather than through processes which require burning fuels which release carbon dioxide.

So it's a really important thing that we can do and relatively easily as well.

We have that technology very well established now.

Now since 2022, over 40% of the electricity generated in the UK has been from renewable energy resources, which is brilliant.

And this percentage of electricity is increasing all of the time.

It's going up very quickly in fact.

In 2024, more than half of the electricity generated in the UK came from renewable resources, which is fantastic.

So we have electrical versions of energy generation in lots of different places now.

We have electric trains and cars for instance, and we also have electric heat pumps which generate electricity for heating and cooling homes, for instance.

So these are all examples of how we are making the change across from fossil fuels to renewable forms of electrical generation.

And by doing so, we are burning less fuel and therefore releasing less carbon dioxide into the atmosphere, which is a great thing to do.

So reducing carbon dioxide emissions will slow down the speed of global warming.

That's really important.

The problem is though, carbon dioxide persists in the atmosphere for a few hundred years.

So even if we cut all of the carbon dioxide out of our emissions now, today, it would still take a couple of hundred years before we could see the impact of that in the atmosphere.

So this is not a quick fix by a long stretch.

And so even by lowering carbon dioxide emissions, it's going to take a long time to undo all the work that we have done over the last couple of hundred years to add all that carbon dioxide into the atmosphere.

It's gonna take another couple of hundred years to undo that and return us back to pre-industrial levels of carbon dioxide in the atmosphere.

So how much electricity in the UK is generated using renewable energy resources? Almost all, about half, or very little? I'll give you five seconds to decide.

Okay, so you should have said that about half is generated by renewable energy resources.

And for the 12 months in 2023/24, over half of the UK's electricity was generated for the first time from renewable energy resources.

So we've seen how carbon dioxide is a substantial cause of global warming.

And methane is the second greatest cause of global warming.

Now about 60% of the methane in the atmosphere is caused by human activities, and these include the decomposition of waste in landfill sites and also from agriculture and from industrial processes.

So these are all releasing methane into the atmosphere.

Now methane that is released during the decomposition of waste in landfill sites and also when fossil fuels are used in industry can be captured and burnt to generate electricity.

So we can catch that methane before it enters the atmosphere and turn it into electricity.

However, when we burn methane, we can't destroy the carbon in it, we can simply rearrange it.

And what we do is rearrange methane into carbon dioxide.

So burning methane converts it into carbon dioxide instead.

Now the carbon dioxide is much less harmful to Earth than the methane was, but nevertheless, it's still a greenhouse gas.

Now, methane is more powerful and more harmful than carbon dioxide because it's a more powerful greenhouse gas.

That means that if we put in equal amounts of methane and carbon dioxide into the atmosphere, we would see that methane would contribute a much greater amount to global warming than carbon dioxide does.

So it's pretty bad news as far as methane's concerned, except that methane only lasts in the atmosphere for about 12 years.

So although it's pretty potent and is really quite devastating for the atmosphere, it doesn't stick around for very long.

So getting rid of methane from the atmosphere and reducing methane emissions will contribute a reduction, a very quick reduction in greenhouse gases in the atmosphere.

So it will be a quick win if you like.

We'll be able to get rid of methane from the atmosphere in just over a decade, which is not a very long period of time at all, especially when you compare that to carbon dioxide, which will hang around in the atmosphere for 100 to 200 years, much, much longer indeed.

So reducing emissions of which gas will slow down the speed of global warming the most quickly? Carbon dioxide, methane, or water vapour? I'll give you five seconds to decide.

Okay, so you should have chosen methane.

Methane will slow down the speed of global warming the most quickly, but reducing carbon dioxide emissions will have a greater, long term effect.

Okay, let's summarise that part of the lesson then by sorting the statements which are bulleted below the table into three groups to compare carbon dioxide and methane.

So some of those statements only relate to carbon dioxide, others only relate to methane and some relate to both.

So sort them out and put them into the correct boxes.

Pause the video and come back to me when you are ready.

Okay, let's check your work.

So the statements which relate specifically to carbon dioxide are: that carbon dioxide contains carbon and oxygen atoms, that it stays in the atmosphere for hundreds of years and that it's produced by burning fossil fuels.

The statements that relate specifically to methane are that it contains carbon and hydrogen atoms, stays in the atmosphere for about 10 years and is produced by buried waste.

And the statements which relate to both carbon dioxide and methane are that reducing its emissions will slow the speed of global warming, that they are both gases at room temperature, they are both greenhouse gases, and they are both produced by agriculture.

So well done if you sorted them all into the correct columns, but do amend your work neatly so that you can understand how you've changed it if you have made any mistakes.

And well done.

Okay, we've come to the end of our lesson today, and I hope you've enjoyed it.

We've seen how the greenhouse effect is a natural process that helps to keep the Earth at a good temperature for life to thrive.

And greenhouse gases in the atmosphere help to keep the atmosphere warmer than it would otherwise be.

And those greenhouse gases include water, carbon dioxide, and methane.

Now adding extra greenhouse gases into the atmosphere enhances the greenhouse effect and causes global warming with rising average surface temperatures.

Now the amount of water vapour in the atmosphere is not directly affected by human activity, but what human activity has directly impacted is the amount of carbon dioxide and methane in the atmosphere.

And if we reduce the emissions of carbon dioxide and methane, then we will slow the speed of global warming.

So I hope you found today's lesson interesting.

Thank you very much for joining me today, and I hope to see you again soon.

Bye.