Lesson video

This lesson is called carbon dioxide in the atmosphere and is from the unit atmosphere and changing climate.

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 explain how changing factors in the carbon cycle affects the amount of carbon dioxide in the atmosphere over time.

Now, we're gonna come across a number of keywords in our lesson today, and 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 carbon cycle before we consider the increasing levels of carbon dioxide in the atmosphere, and then look at how we monitor those carbon dioxide levels.

So are you ready to get started? I certainly am.

Let's go.

Now, the carbon cycle is a complex process which charts the movement of carbon from the atmosphere into living organisms into the soil and the oceans and around through various different processes.

And if we study the carbon cycle and understand how carbon is moving outta the atmosphere and then getting put back into the atmosphere, it may help us to understand what is causing the carbon dioxide levels in the atmosphere to vary over time.

So some processes remove carbon dioxide from the atmosphere.

For instance, photosynthesis by plants and algae.

This removes a significant amount of carbon dioxide outta the atmosphere.

Oceans are significant carbon removers as well.

They dissolve carbon dioxide from the atmosphere too in significant quantities.

And so we call both plants and oceans carbon sinks because they are removing more carbon from the atmosphere than they are putting back in, and therefore are called carbon sinks.

Now carbon can move within and between carbon sinks.

So once it's been stored within the ocean, then organisms within the ocean can store it in their shells and bones.

Dead organisms lying on the land can then be converted into soil through decomposition.

And again, carbon can therefore be stored within the soil.

Once carbon has been stored within the soil and within the sediment at the bottom of the ocean, it can then be processed through the rock cycle and stored as fossil fuels or as rocks simply as rocks within the earth structure.

And carbon may also be transported between living organisms. So for instance, animals that eat plants will transfer the carbon that is stored within plant matter into their own bodies, and then if animals eat animals, that carbon moves again from one animal to another.

So there's plenty of ways that carbon can move from one carbon sink, such as plants or the oceans into other carbon sinks such as rock infrastructure, fossil fuels, and the soil.

So let's quickly check our understanding.

Which of the following transfer carbon dioxide into a carbon sink? Photosynthesis by plants, respiration by plants and animals, combustion of fossil fuels or dissolving into oceans.

I'll give you five seconds to think about it.

Okay, so you should have said that the processes of photosynthesis and dissolving into oceans both transfer carbon dioxide into a carbon sink.

Well done.

Now we've seen how carbon dioxide can be removed from the atmosphere.

Well, carbon dioxide can also be put back into the atmosphere as part of the carbon cycle.

And there are several processes which contribute to this, including plant and animal respiration, combustion of fuels.

So if fossil fuels have stored carbon underground for many, many years, many millions of years, and we dig it up and burn it, then that puts carbon dioxide back into the atmosphere through complete combustion and decomposition of dead and decaying matter.

So dead organisms, waste products such as poo and we such as faeces and urine when they get decayed back down again, all of these processes release carbon dioxide back into the atmosphere.

So which of the following transfer carbon dioxide out of a carbon sink? Photosynthesis by plants, respiration by plants and animals, combustion of fossil fuels or dissolving into oceans.

I'll give you five seconds to think about it.

Okay, so you should have said that respiration by plants and animals and combustion of fossil fuels both transfer carbon dioxide out of a carbon sink and back into the atmosphere.

Well done.

So what I'd like you to do is to summarise the carbon cycle and by describing what is happening at each stage within the diagram.

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

Okay, let's check what we've written.

So for stage one, you should have said that that is representing removing carbon dioxide from the atmosphere.

Stage two is carbon dioxide dissolving into the oceans, and stage three is carbon dioxide in the oceans forming carbonates in shells and animal bones.

In stage four, this is the process over millions of years where fossil fuels are formed.

Stage five is the transfer of carbon into animals from plants when they eat plants.

Stage six is the waste materials and dead organisms returning carbon to soil.

Number seven is where decomposers breakdown dead and decaying matter and return carbon dioxide back into the atmosphere.

Stage eight is the combustion of fossil fuels releasing carbon dioxide into the atmosphere.

And you can see that that is a two step process that we have to dig up the fossil fuels first before we can burn them to release the carbon dioxide into the atmosphere.

And finally, stage nine is where plants and animals respire releasing carbon dioxide back into the atmosphere.

Did you get all of those stages correct? Well done if you did.

And make any amendments if you need to.

Okay, let's move on to the next stage of our lesson where we're gonna look at how levels of CO2 in the atmosphere are increasing.

Now we've seen how there are a number of different processes which release carbon dioxide from a carbon sink back into the atmosphere.

And combustion of fossil fuels was one of those where we have to dig up the fossil fuels from the earth in the first place and then burn them through combustion to release carbon dioxide into the atmosphere.

So this is a process where we are burning fuel, coal, oil, or gas with oxygen in a complete combustion reaction to form carbon dioxide and water, both of which are gases and get released back into the atmosphere.

We've also seen from the carbon cycle how carbon dioxide is removed from the atmosphere through the process of photosynthesis.

And photosynthesis is essentially the reverse process where carbon dioxide and water are combined by the plant to make glucose, which is essentially a form of fuel and oxygen.

So combustion of fossil fuels and photosynthesis are opposite processes working in the opposite direction from each other.

However, since the Industrial Revolution, human activities releasing carbon dioxide through the combustion of fossil fuels have far outstripped the amount of carbon dioxide that plants have been able to remove from the atmosphere.

And so there has been a real imbalance in these two processes where combustion releasing carbon dioxide into the atmosphere has far outstripped the amount of carbon dioxide that plants have been able to remove from the atmosphere instead.

And in the last 200 years, human activities have increased the amount of carbon dioxide released into the atmosphere by about 50%, so that is an enormous increase in the amount of carbon dioxide being expelled into the atmosphere all through various forms of burning of fossil fuels.

So if we burn fossil fuels, we very quickly release carbon dioxide into the atmosphere through that process of combustion.

However, what we've also been doing at the same time is felling trees and significant and very rapid deforestation has at the same time as us releasing vast quantities of carbon dioxide into the atmosphere through combustion of fossil fuels, deforestation has removed the ability of plants to remove carbon dioxide from the atmosphere because we've chopped the trees down and stopped them from completing photosynthesis and therefore made the situation far worse.

Now Lucas says, "To reduce the levels of carbon dioxide in the atmosphere, we should just plant more trees." Which sounds like a very sensible suggestion given that photosynthesis is the reverse process of combustion.

And we know that trees photosynthesizing remove carbon dioxide from the atmosphere.

The problem is that we are putting so many carbon emissions into the atmosphere by burning fossil fuels.

We would need to plant a vast number of extra trees across the entire planet surface in order to combat the amount of carbon dioxide that we are expelling into the atmosphere from the combustion of fossil fuels.

And even if we were to plant more trees because of the vast rate at which we are burning fossil fuels, the rate of carbon dioxide increasing within the atmosphere will continue to rise because we are simply not doing enough to counter those emissions and absorb carbon dioxide back outta the atmosphere at a rate that's even anywhere near close to the rate at which we're expelling the carbon dioxide into the atmosphere.

So which statement correctly explains why carbon dioxide levels in the atmosphere have increased? Is it A, because CO2 has been added more quickly than it has been removed, or B, because CO2 has been added just as quickly as it has been removed, or C, because CO2 has been added less quickly than it has been removed, or D, because CO2 has been added more quickly than it was before.

I'll give you five seconds to think about it.

Okay, so you should have said that statement A is correctly explaining why carbon dioxide levels in the atmosphere have increased.

Well done.

So we've seen how we are increasing the amount of carbon dioxide being released into the atmosphere.

And the problem with this is that carbon dioxide is a greenhouse gas, and that means that as the levels of carbon dioxide increase in the atmosphere, it in turn increases the earth's temperature.

Now this has knock on repercussions because as the temperature of the earth increases, the amount of carbon dioxide that oceans can store reduces because warmer oceans can dissolve less carbon dioxide.

And so as the earth is warming less carbon dioxide is being stored in the oceans, and more carbon dioxide is being expelled from the oceans into the atmosphere.

And this is compounding the problem because we are putting a lot of carbon dioxide into the atmosphere already through our various activities, including burning of fossil fuels.

And then through the increase of the temperature on the earth, this is being added to by the oceans which are giving up carbon dioxide from the store in the ocean because of an increase in temperature.

So this is a complex process which has many repercussions to it.

So increasing ocean temperatures have led to what? A, more carbon dioxide dissolved in the oceans, B, no change in the amount of carbon dioxide dissolved in the oceans, or C, less carbon dioxide dissolved in the oceans.

I'll give you five seconds to think about it.

Okay, so you should have said that increasing ocean temperatures has led to less carbon dioxide being dissolved in the oceans.

Well done.

So what I'd like you to do now is to analyse the graph, as you can see on the screen, showing the atmospheric carbon dioxide levels in parts per million, that's ppm, per year starting from 1960 or just before and ending in 2023.

So what I'd like you to do is to firstly describe the pattern shown in the graph before explaining how increasing ocean temperatures have affected the amount of carbon dioxide in the atmosphere.

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

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

So firstly, I asked you to describe the pattern shown in the graph, and you might have written that between 1960 and 2020, the amount of carbon dioxide in the atmosphere has increased.

And then I asked you to explain how increasing the ocean temperatures have affected the amount of carbon dioxide in the atmosphere.

And you might have written that as the ocean temperatures have increased, the amount of carbon dioxide dissolved in them has decreased, and this has caused an increase in the amount of carbon dioxide in the atmosphere.

So did you get both of those answers correct? Well done if you did.

Okay, let's move on to the last section of our lesson now, which is about how we monitor carbon dioxide levels.

Because monitoring carbon dioxide levels in the atmosphere is really important to understand how quickly this process of global warming is occurring.

And although countries are releasing different quantities of carbon dioxide for each of them, carbon dioxide once it's in the atmosphere, can be very easily mixed and spread around the earth.

And so monitoring carbon dioxide levels in one location within the earth's atmosphere gives us a reasonably good idea of what the atmospheric carbon dioxide levels will be anywhere else across the surface of the earth.

Now, the first readings of carbon dioxide levels were taken in 1958 from the Mauna Loa Observatory in Hawaii.

And you can see where Hawaii is on the global map off to the west side of the United States of America and fairly near to the equator.

And although this was the first location where carbon dioxide levels were monitored from, carbon dioxide levels are now monitored globally in many, many locations.

Now the amount of carbon dioxide present in the atmosphere is measured in parts per million.

I've already mentioned that when you were looking at the graph earlier on ppm.

And in 1750, there were 250 parts per million of carbon dioxide in the atmosphere.

So this means that for every million atoms or molecules in the air, 250 of them were carbon dioxide molecules.

Now this gives us about six quintillion, six quintillion carbon dioxide molecules in just one litre of air as we are breathing it.

That's six with 18 zeros following it.

That's how many carbon dioxide molecules are present within a litre of atmosphere, well at least where back in 1750 when there were 250 parts per million of carbon dioxide in the atmosphere.

However, by 2023, this had increased to 419.

3 parts per million.

You can see that that is an absolutely astonishing increase in parts per million.

And this works out to being nine quintillion or nine with 18 zeros following it, particles of carbon dioxide in a litre of air.

So an increase of three quintillion particles of carbon dioxide for every litre of air.

That is an enormous increase in carbon dioxide levels from 1750 to the present day.

So burning fossil fuels in a UK city produces carbon dioxide.

Where can these carbon dioxide molecules travel to? A, to the edges of the city, B, to a distant countryside, C, to a Spanish beach on mainland Europe or D, to a Hawaiian island in a large ocean.

I'll give you five seconds to decide.

Okay, so you should have decided that all of these answers are correct, that carbon dioxide will travel across the globe through the atmosphere.

Well done if you spotted all of those.

Now, monitoring the carbon dioxide levels in the atmosphere is a really important thing to do from a scientific perspective.

And the graph that you can see on screen there now is drawn from data which is collected from Mauna Loa, from the Observatory in Hawaii.

Now Hawaii is in the northern hemisphere, it's just above the equator.

And you can see how the levels of carbon dioxide alter as each year progresses.

Now, the overall trend is for an increase in carbon dioxide levels, but if you zoom in and look a little bit more closely, you can see that actually the line is going up and down, up and down, up and down across all of those years.

So you can see that this level is fluctuating.

But why is that the case? Well, it's fluctuating because during the summertime in the northern hemisphere, the carbon dioxide levels drop because of the growth of plants, the effect of photosynthesis on carbon dioxide levels on the atmosphere is noticeable.

It significantly reduces the amount of carbon dioxide present within the atmosphere.

And then again, in winter when growth in the northern hemisphere stops or at least reduces, there is less plant growth and therefore there is less photosynthesis taking place.

And there is also more plant decay.

And plant matter decaying releases carbon dioxide into the atmosphere.

So in winter with less photosynthesis and more plant decay happening, carbon dioxide levels increase again.

Now this is particularly relevant for the northern hemisphere because there is significantly more land mass twice as much land mass in fact in the northern hemisphere than there is in the southern hemisphere.

So this feature is going to be much more obvious within the northern hemisphere than it will in the southern hemisphere.

So what has happened to global atmospheric carbon dioxide levels since 1958 when direct measurements began, have carbon dioxide levels increased? Have they not changed or have they decreased? I'll give you five seconds to think about it.

Okay, so you should have said that carbon dioxide levels have increased.

Well done.

So what I'd like you to do now as our final task for today's lesson is to explain why the levels of carbon dioxide in the atmosphere go up and down during each year.

So this is essentially fleshing out your answer to the previous task, adding some more detail in to describe why those little fluctuations are present within the data.

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

Okay, let's see what you might have written.

So to explain the smaller fluctuations within the graph rather than the overall trend, you might have written that there are seasonal changes to the carbon dioxide levels in the atmosphere, and this is caused by changes in plant growth in the northern hemisphere, which has much more plant life than in the southern hemisphere.

And in more detail, you might have added that in the summer plants photosynthesize, and this reduces atmospheric carbon dioxide levels, whereas in the winter there is less photosynthesis occurring and some plant matter decomposes causing an increase in the atmospheric carbon dioxide levels.

And you'll see that around you in wintertime when plants lose their leaves die back.

And the general horticultural spaces within the UK look much more bare than they do in full summer.

Now, this is true every year these fluctuations occurring, but the overall trend over the years since 1958 is an increase in atmospheric carbon dioxide levels.

So check your answer over, make sure you've got all those relevant points and well done indeed.

Okay, we've come to the end of our lesson now.

So thank you very much for joining me today.

In our lesson today, we've seen how the combustion of fossil fuels adds carbon dioxide to earth's atmosphere and how carbon dioxide when added to the atmosphere in one place will over time spread throughout the earth's atmosphere.

We've also seen how plants act as carbon sinks because as they grow, they remove carbon dioxide from the atmosphere through the process of photosynthesis.

But we've also seen that the de combustion of plant matter and the burning of plant matter in the form of say fossil fuels or biomass, returns carbon back into the atmosphere in the form of carbon dioxide.

We've also seen how when the temperature of the earth increases, the ocean temperature also increases.

And this means that the oceans are able to store less carbon dioxide and release carbon dioxide into the atmosphere as a result.

And ultimately, all these changes to carbon dioxide levels is being driven by human activity where we are adding much, much more carbon dioxide to the atmosphere than can be removed by natural processes such as photosynthesis and dissolving within the oceans.

So I hope you found our lesson interesting today.

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

Bye.