Lesson video

This lesson is called atmospheric carbon and is from the unit carbon cycle and climate change.

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 how too much carbon dioxide in the Earth's atmosphere is contributing to global warming.

And in our lesson today, we're gonna come across a number of keywords.

They're listed up here on the screen for you now.

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

Now in our lesson today, we're going to first of all look at the combustion of fuels, before we consider carbon dioxide as a greenhouse gas.

So, are you ready to go? I certainly am.

Let's get started.

Now I'm sure you have come across coal, oil and gas before, and all of these are naturally occurring fossil fuels which contain hydrocarbons.

And hydrocarbons are molecules that contain only hydrogen and carbon, hence the name hydrocarbon.

Examples of hydrocarbons include methane, ethane and propene, and these are all types of hydrocarbons found within various different fossil fuels.

So methane is a hydrocarbon because it only contains one carbon atom and four hydrogen atoms. So its molecular formula is CH4.

Ethane has two carbon molecule, two carbon atoms, and six hydrogen atoms. And so its molecular formula is C2H6 and that's ethane, but that's also a hydrocarbon because it only contains hydrogen and carbon.

Another hydrocarbon is propene and propene contains three carbon atoms and six hydrogen atoms. And so has the formula C3H6, but that's a slightly different structure from ethane and methane because there's a double bond in its structure.

Can you see that double line between two of the carbons? That indicates a double bond.

But all of these molecules and plenty more besides, including those found within petrol and diesel are all types of hydrocarbons, because they contain only hydrogen and carbon.

So which of the following are hydrocarbons? Methane, ethane, propanol and butene? Use the molecular formula to help you decide.

Okay, so you should have chosen methane, ethane and butene as hydrocarbons.

Propanol is not a hydrocarbon because it also contains oxygen.

Well done if you spotted that.

Now, fossil fuels and hydrocarbons are really, really useful and fossil fuels in particular are useful because they allow us to provide energy.

So fossil fuels used as liquids in our cars.

We can also burn fossil fuels, natural gases in our stoves to cook our food, and we can also use coal, oil and gas in power stations to generate electricity.

So burning fossil fuels is a really, really useful way of providing energy for many of the things that we do around our home and in our businesses.

Now, when we're burning fossil fuels, what we're doing is combusting fossil fuels because the word combustion is the scientific term for burning.

So when you're burning logs of wood on your fire for instance, you're combusting that wood.

Or if you're burning a candle, you're combusting that candle.

Now, in order for combustion to be successful, it requires three key things as shown in the fire triangle on your screen.

Firstly, it requires a fuel to burn.

It also needs some heat in order to make that combustion process happen.

And lastly, it requires oxygen.

So which three things are required for combustion? Fuel, heat and oxygen, fuel, heat and carbon dioxide, or fuel, water and oxygen? I'll give you five seconds to decide.

Okay, so you should have chosen fuel, heat, and oxygen as the three things required for combustion.

Well done.

So if we are saying that to combust something we need fuel, heat and oxygen well, what does that actually look like? Well, when we're combusting a hydrocarbon such as coal, oil or gas, what we are doing is burning it in oxygen.

So the molecule of hydrocarbon, in this case the molecule of methane as pictured on the left there, that's the hydrocarbon and that forms the fuel.

Now, in order to burn it, to combust it, we need oxygen.

And that is what the hydrocarbon reacts with from the air.

That's where oxygen is coming from.

It's found in the atmosphere and it reacts with the hydrocarbon as part of the combustion process.

This forms carbon dioxide and it also forms water.

So these are the products of the combustion process.

So the fuel plus the oxygen, form carbon dioxide and water.

So the general equation for combustion is exactly that.

Fuel plus oxygen leads to carbon dioxide and water.

And this is true for any fuel be that wood, coal, oil, gas, doesn't matter as long as it is a fuel.

If it is combusted, it will be burning in oxygen to form carbon dioxide and water.

So the fuel and the oxygen form the reactants of this process, whereas the carbon dioxide and the water are the products, the things that are made.

Now, the products of combustion, water and carbon dioxide are both compounds.

This means that they both contain two, or more different elements chemically joined together.

So in carbon dioxide, carbon dioxide contains one carbon atom and two oxygen atoms, which are chemically fused together to form carbon dioxide.

And you can see that in the diagram there.

And that is why its molecular formula is CO2, because there's one carbon and two oxygen atoms within that molecule, within that compound.

Whereas with water, water is a compound of oxygen and hydrogen.

So water contains one oxygen atom and two hydrogen atoms and so its molecular formula is H2O.

And so water is a compound.

So what I'd like you to do now, is to summarise our learning so far, by firstly labelling the fire triangle showing the three things that are needed for combustion, and then by completing the equation to show the products of combustion, where we're starting off with fuel and oxygen reacting together.

After you've done that, I would like you to complete the table, stating the number of atoms of each element, which is present within the compounds.

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

Okay, let's see what you've written.

So firstly, I asked you to label the fire triangle and you should have added fuel, oxygen and heat to it.

Now really you should be putting fuel along the bottom because that is really where the fuel will sit in the bottom of the fire, with oxygen and heat up the sides of the triangle.

Then I asked you to complete the equation to show the products of combustion and you should have added carbon dioxide and water to the right side of that word equation.

Then finally, I asked you to complete the table, and for methane you should have said that that contains one carbon atom and four hydrogen atoms. For water, there are two hydrogen atoms and one oxygen atom.

And for carbon dioxide there's one carbon atom and two oxygen atoms. So check your work over, make sure you've got it all correct and well done indeed.

Let's move on to consider how carbon dioxide is a greenhouse gas.

So we know that when we combust fuels, we are releasing carbon dioxide and water vapour into the atmosphere.

And so the more fossil fuels that we burn, the more carbon dioxide gets released.

Now, burning large quantities of fossil fuels happens in large portions of industry, where fossil fuels are required for the energy needed for the processes that are used in the manufacturing of whatever it is that they're producing.

Now, currently in the atmosphere, there is 0.

04% carbon dioxide.

So there's a very small percentage of carbon dioxide present within the atmosphere.

The vast majority of it is nitrogen gas.

Now, if there's 0.

04% carbon dioxide in the atmosphere, then what this means is, that there are about 400 in every million gas particles that are carbon dioxide.

So if you scooped up one million gas particles and you counted them all, you would find about 400 of them were carbon dioxide.

And so this means that there are about 400 parts per million ppm of carbon dioxide in the atmosphere at the moment.

Now, if we breathe in a lung full of atmosphere, of air, then actually what we're doing then is breathing in the equivalent of three quintillion particles of carbon dioxide.

That's a three with 18 zeroes following it.

So that's how many carbon dioxide molecules are present within every lung full of air, three quintillion of them.

Now that sounds like an awful lot, but it still is only 0.

04% of all of the molecules that we have inhaled in one breath of air.

Now in 1750, the number of carbon dioxide molecules per million in the atmosphere was about 250.

So in 1750, for every lung full there was about 250 parts per million of carbon dioxide, and that was the natural concentration of carbon dioxide at the time.

Now by 1950, so 200 years later, that level had increased to around 310 parts per million.

And by 2024, so another 75 years later, the concentration of carbon dioxide in the air was 425 parts per million.

So it's gone up from 250 parts per million in 1750, to 425 parts per million in today's world.

That's really quite a staggering increase and equates to about three quintillion extra particles of carbon dioxide for every breath of atmosphere that you inhale.

That's three with 18 zeros following it, three quintillion.

So what is the approximate percentage of carbon dioxide in the atmosphere? Is it 4%, 0.

4%, or 0.

04%? I'll give you five seconds to decide.

Okay, so you should have chosen C, 0.

04%.

That's the approximate percentage of carbon dioxide in the atmosphere at the moment.

Well done if you've got that correct.

Now, what's the big deal about carbon dioxide, 'cause we keep talking about the amount of carbon dioxide in the atmosphere, so it's obviously a big deal, but what is it about carbon dioxide that makes it such a big deal? Well, if we imagine with the sun and the Earth, we know that the sun is shining down on the Earth, and some of the radiation that we're getting from the sun is infrared.

It feels warm.

So infrared radiation is coming from the sun to Earth, and some of that radiation is reflected off the surface of the Earth straight back into space.

Some of it, in fact the majority of it, stays and warms the surface of the Earth, which is why rocks feel warm for instance when they've been baked in sunshine.

Now some of that radiation off the surface of the Earth, is reflected back into the atmosphere.

And when it is reflected back into the atmosphere, the greenhouse gases absorb that radiation and then they re-emit it back out and spread it around the atmosphere.

So they're taking warmth, infrared radiation, which is being reflected off the surface of the Earth, they're absorbing that, then they're re-emitting it back out into the atmosphere.

And what this does is circulate that heat around the atmosphere and warm the atmosphere up.

Now this reduces the amount of heat that is lost to space, keeping more heat inside the atmosphere and trapped by the surface of the Earth.

Now, one of those greenhouse gases is carbon dioxide.

So one of the gases, which is doing this re-emitting and moving heat around the atmosphere is carbon dioxide.

And by doing this, what it does is raise the temperature of the Earth, the average temperature of the Earth.

It raises it by about 20,25 degrees from a really chilly minus 18 degrees centigrade, to a much more pleasant 14 degrees centigrade.

So what do greenhouse gases do? Do they absorb infrared IR radiation reflected off Earth's surface? Do they reflect infrared radiation back into space, or do they keep the temperature of Earth's atmosphere higher than it would be without them? I'll give you five seconds to decide.

Okay, so you should have said that greenhouse gases, absorb infrared radiation reflected off the Earth's surface and keep the temperature of Earth's atmosphere higher than it would be without them.

Well done if you spotted both of those.

Now, as I've said, greenhouse gases are really important for life on Earth because they help to maintain a nice warm temperature on Earth.

It's not too warm, but it's warm enough for life to thrive.

And it also because of that, reduces the number of extreme weather events that happen across the globe.

Now we're adding more greenhouse gases into the atmosphere and this is causing the Earth's average temperature to rise.

Now there's a lot of very solid evidence to demonstrate a link between the increase in carbon dioxide levels in the atmosphere and the increase in the average global temperature.

And you can see on the graph on the screen there, how the temperature has increased over the last 130 years or so.

Now this increase in temperature is called global warming, and it is because of the carbon dioxide, plus methane and nitrous oxide, which are also greenhouse gases in the atmosphere that global warming is happening.

Now global warming is problematic because, a warmer planet is not a more stable planet, but actually a warmer planet is much more unstable.

Weather patterns become much more unstable and harder to predict, and they also become much more extreme.

So some regions will become hotter and drier, whilst others will become wetter and colder.

And this is all climate change, changes in global weather patterns.

So these changes in global weather patterns are very difficult to cope with.

They can be very destructive for a start, but they also make it much more difficult for plants and animals to survive and thrive.

As well as the greenhouse effect causing more common extreme weather events, it is also threatening the biodiversity, the range of plants and animals living on Earth as well.

So what we need to do is add less carbon dioxide into the atmosphere.

And if we can do this, then the global average temperature will not rise as much and may indeed start to come back down again.

But this requires quite a considerable reduction in carbon emissions and it will also take a very long time to occur, because carbon dioxide stays in the atmosphere for 50 to 100 years or more, before it works its way out in other processes.

So if we start to cut carbon emissions now, it's not going to really come into effect for another 50 to 100 years perhaps when you are grandparents and you're considering the fate of your grandchildren.

We can also reduce the amount of methane being put into the atmosphere.

Methane is another greenhouse gas and the turnaround on methane is much shorter than it is for carbon dioxide.

So we would see a reduction in global warming relatively quickly with a reduction in methane production.

However this would only be a fairly short-lived impact, because ultimately what we need to do is reduce the amount of carbon dioxide in the atmosphere if we are after a long-term solution, which is what we really need to achieve.

So what impact do increasing levels of greenhouse gases have on global temperatures? Is it that the global temperatures decrease? Is it that global temperatures stay the same, or is it global temperatures increase? I'll give you five seconds to decide.

So you should have said that increasing the level of greenhouse gases causes global temperatures to increase.

Well done if you spotted that.

So what I'd like you to do, is to firstly describe the trend shown in the graph for the Earth's average temperature over time.

So look at the graph very carefully and describe the trend that you're seeing within that data.

And then I'd like you to complete the sentences to explain the cause of global warming.

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

Okay, let's see what you've written.

So firstly, I asked you to describe the trend shown in the graph for Earth's average temperature over time.

And you should have said, "The graph shows that Earth's average temperature "fluctuates each year, "but has generally increased over time".

And possibly you've gone on to add that since around 1980, the rate of increase has become more rapid.

Well done if you've managed to put both of those points down.

Then I asked you to complete the sentences to explain the cause of global warming.

So you should have said the Earth's surface is heated by infrared radiation from the sun.

Greenhouse gases absorb some of infrared radiation from the Earth's surface.

Human activity has quickly increased the amount of carbon dioxide and other greenhouse gases in the Earth's atmosphere.

These absorb more infrared radiation from Earth's surface, preventing it from escaping into space.

This increases the temperature of Earth's atmosphere.

Well done if you've got all of those words correct, but do update any incorrect ones, so that your sentences read correctly and well done.

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

We've seen how many fuels contain hydrocarbons, and these are molecules made of hydrogen and carbon atoms only.

Methane, CH4 is a hydrocarbon with molecules containing one carbon and four hydrogen atoms and carbon dioxide CO2 and water H2O, are often produced by the combustion of a hydrocarbon when it is burnt in oxygen.

Now carbon dioxide is a greenhouse gas.

It makes up about 0.

04% of the Earth's atmosphere, and it can absorb infrared radiation from the Earth's surface, reducing the amount of heat that escapes into space and causing the atmosphere to heat up.

The rising average temperature on Earth's surface is caused by an increase in the level of carbon dioxide and other greenhouse gases in the atmosphere, and this is called global warming.

So I hope you've enjoyed our lesson today.

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

Bye.