Lesson video

This lesson is called "Deforestation affects the carbon and water cycles," and is from the unit "Climate Change and Biodiversity." 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 see how deforestation has significant impacts on us, in particular by looking at both the carbon and the water cycles.

And we're gonna have a look at ways of reducing these impacts.

So 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 look at the impact of deforestation on the carbon cycle before we consider the impact of deforestation on the water cycle.

So are you ready to go? I certainly am.

So let's get started.

So let's look at carbon, first of all.

Carbon is an element, just like hydrogen and oxygen are also elements.

And it is a very important element because some of the properties that carbon has makes it incredibly useful for many different things.

For instance, all living organisms, every single one of them requires carbon because carbon is needed in order to build the bodies of living organisms. And that's because carbon is found in carbohydrates.

That's what the word carbo means in carbohydrates.

They're also used to make proteins, and also found in fats.

And carbohydrates, proteins, and fats are all absolutely fundamental molecules used to build our bodies and the bodies of all living organisms, whether they are bacteria, plants, fungi, or animals, and enable these bodies to function.

So carbon is an essential element for all living organisms. Now, carbon is found all through the Earth, and that is because it is so fundamental.

So we find carbon in the atmosphere, in the form of carbon dioxide primarily, but also in the form of methane.

We also find carbon in living organisms, be them alive or dead, and that could be recently dead or very, very long dead like fossilised organisms. So the fossilised remains of dinosaurs, for instance, still contain carbon.

And also all of the living organisms, every single one of them contains carbon as well.

And we also find carbon within fossil fuels, which are buried very deep underground.

So this is coal, oil, and natural gas.

And these have been made from previously living organisms like plants and microorganisms. And so the carbon that was in their body has been converted through a long, slow process to create coal, oil, and gas.

And so we find carbon in both a gaseous form and a liquid form and a solid form throughout all of the different layers of the Earth.

Now, carbon moves between these layers in a constant process called the carbon cycle.

Naturally, there's lots of processes within the carbon cycle that allows carbon to be moved from the atmosphere into living organisms, into the soil and then back into the atmosphere.

And we're gonna have a look at some of those stages today, particularly those where trees are involved and to see how the carbon cycle is impacted by deforestation.

So those important stages include the fact that when living organisms die, so that could be animals like humans and cows, for instance, as shown in the picture, or trees and other plants, or fungi, bacteria, any living organisms. When they die, their bodies will eventually get processed into firstly the soil and then can eventually get moved into a long-term store of carbon, which is fossil fuels.

So this is coal, oil, and gas.

So that's one process.

It takes a very long time for that to happen, but it can happen.

So we could eventually, in many hundreds of thousands of years, turn into fossil fuel.

Then another important part of the carbon cycle is that we dig up those fossil fuels.

So we extract coal, oil, and gas from deep underground and then we burn it.

And burning is a process called combustion.

That's the scientific term for burning.

And when we combust fossil fuels, we release that carbon that was stored in the fossil fuels back into the atmosphere.

And so these two significant processes are really important for moving carbon through the carbon cycle.

But we've missed a bit.

How does carbon get into the bodies of living organisms, so plants and animals, for instance, in the first place? Because we can see it being turned from their bodies into fossil fuels and from fossil fuels back into the atmosphere.

But how did it get into their bodies initially? Well, organisms like animals and fungi cannot absorb carbon directly from the atmosphere because the carbon that we do absorb, we breathe back out again.

So the carbon dioxide in the atmosphere enters our body into our lungs and then goes straight back out again when we exhale.

However, plants and other photosynthetic organisms, like algae for instance, can absorb carbon out of the atmosphere.

And in fact, that is an essential part of how they function, because the process of photosynthesis involves combining carbon dioxide, which has been taken out of the atmosphere, with water in order to make glucose, which allows plants and other organisms which photosynthesize to build their body.

It's called biomass.

And the biomass is made up of carbon-based molecules, carbohydrates, proteins, and fats.

And these are built using the carbon that was in the atmosphere, but has been collected by the plants and turned into carbohydrates, proteins, and fats via photosynthesis.

And then for animals to obtain carbon, we then need to eat the plants or we need to eat animals that have eaten plants.

So we can see that in the diagram on the screen, how we could eat apples from the tree, for instance, and take the carbon in the apple and turn that into carbon-based molecules within our body.

Or the cow could eat grass and therefore turn the carbon in the grass into molecules of its body.

And then we can eat the cow and turn the carbon within the cow's body into carbon-based molecules in our body.

And so eating the biomass of producers is the way of transferring carbon from producers into other organisms within the food chain.

So which processes enable carbon from the atmosphere to be used and stored in the bodies of living organisms? Do consumers breathe it in? Do humans burn it as fossil fuels? Do organisms die and become fossil fuels? Or does photosynthesis in producers enable carbon from the atmosphere to be used and stored? So I'll give you five seconds to think about it.

Okay, so the process which enables carbon from the atmosphere to be used and stored in the bodies of living organisms is D, photosynthesis in producers.

So producers are photosynthesizing, and by doing so, extracting carbon in the form of carbon dioxide from the atmosphere and turning it into the molecules within their body.

Well done if you got that correct.

So we've seen how trees and other plants and producers generally are essential in the carbon cycle because if they weren't there, then carbon dioxide would not be extracted from the atmosphere and carbon wouldn't be turned into biomass within the producer's bodies and then wouldn't be able to be passed on to other organisms within the food chain to be made into their bodies.

So photosynthesis is an essential process that is enabling carbon to be turned into many other organic molecules like carbohydrates, proteins, and fats.

Now, forests play an extremely important role in regulating carbon levels within the atmosphere.

So forests are responsible for removing a quarter, one-quarter of all of the carbon dioxide that we emit into the atmosphere.

However, if we chop forests down, and we do very, very quickly all of the time, this process of deforestation is removing trees.

And that means that there are far fewer trees present on Earth to absorb carbon dioxide from the atmosphere.

And this means that the emissions that we are pumping into the atmosphere when we are burning fossil fuels aren't going down as quickly as they should because there are fewer trees in order to do that.

And this means that because carbon dioxide levels are increasing in the atmosphere, global warming is happening and that is driving climate change.

And so deforestation directly increases climate change.

Deforestation doesn't just involve the chopping down of trees, but usually it also involves the burning of trees, which has an extra layer of problem to it because not only have we removed the trees from the forest and so they cannot remove carbon dioxide from the atmosphere anymore, but what we've done by burning or combusting the trees is release the carbon that was stored within their bodies back into the atmosphere.

So we've doubled the problem.

As carbon dioxide levels increase within the atmosphere, we will see ever increasing climate change.

And climate change involves extreme weather events becoming more frequent.

So what are extreme weather events? What do we mean by that? Well, some extreme weather events include: increased heat and heat waves, which are unusual and usually longer periods of hot weather than would normally be experienced by that area, leads to drought.

And when plants have died through drought, they are now no longer living and therefore no longer photosynthesizing.

So carbon dioxide is not being removed from the atmosphere because the plants are dead.

And it also increases the likelihood of wildfires.

And we've seen a lot of that in the news over the last few years where severe wildfires are becoming much more frequent and much larger and lasting for longer than they would normally have done.

And, of course, when plants are burning in a wildfire, the carbon that was stored within their body is being released back into the atmosphere just like when trees are burned through deforestation.

Now, that's one set of extreme weather events.

Extreme weather also includes heavy rainfall.

And when heavy rainfall happens through severe storms, this leads to flooding.

And, of course, flooding has an impact on plants because many plants cannot grow in flooded land and so they end up dying.

And what this tends to impact on is the availability of crops because it's often crops which are flooded because of the way the land has been managed.

And we'll look at that in a little bit later in this lesson.

And if crop land is flooded and the crops die, then this impacts on our food security, on the availability of food, how easy it is to get food, to grow it, to harvest it, and to get it to our dinner tables.

That is impacted because the crops have been damaged in the first place through flooding.

And so extreme weather events involving high wind and rain levels impact food security by damaging crops.

So climate change will impact the carbon cycle and it will also impact our food security.

Now, if we protect and restore forests, we will be able to reverse some of these changes because when we replant and restore forests and when we stop forests from being chopped down in the first place, we allow trees to carry on growing and therefore maintain their essential role within the carbon cycle.

And therefore, protecting and restoring forests will limit the effects that we are having through the emissions that we are making into the atmosphere on climate change.

So how do we do that? How do we protect and restore forests? Well, we can protect forests by preventing deforestation, by monitoring and policing the land, and by putting into the law protection for forests.

And that means that we can stop forests from being cut down and turned into agricultural land or built on for homes and industry.

We can restore forests by replanting them, and this is called reforestation.

So we can reforest land by planting trees on land that has turned into other uses such as farmland.

So who correctly explains an effect of deforestation? So Alex says, "Burning the trees releases all the carbon they absorbed back into the atmosphere." Sofia says, "Deforestation absorbs a quarter of our carbon dioxide emissions every year." And Jun says, "Chopping down trees means they can no longer absorb carbon dioxide." But who is correct? I'll give you five seconds to decide.

Okay, so you should have said that Alex and Jun are both correctly explaining an effect of deforestation.

Well done if you chose both of them.

So what I'd like you to do is to read the statements and decide whether you are sure they are correct, think they are correct, think they are incorrect, or sure they are incorrect.

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

Okay, let's check your work.

So for statement A, trees and other producers absorb carbon from the atmosphere, you should have said that that is correct.

For statement B, consumers depend upon trees and other producers for carbon, you should have said that that is correct.

And for statement C, deforestation has no effect on the carbon cycle, you should have said that that is incorrect.

And well done if you got all of those answers correct.

So let's have a look at three more statements and do the same thing.

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

Okay, let's check your work.

So for statement D, trees and other producers absorb carbon for photosynthesis, you should have said that that is correct.

For statement E, forests absorb one quarter of the annual carbon emissions by humans, you should have said that that is correct.

And for statement F, deforestation increases climate change, you should have said that that is correct.

Well done if you got all three of those correct as well.

Okay, let's move on now to looking at how deforestation impacts the water cycle.

All living organisms require water.

Plants require water and can absorb it through their roots, and animals require water and drink it.

And all organisms require water because about 70% of the cell cytoplasm, so that's the jelly-like substance within the cell itself, is made up of water.

Now, water is essential in the cell, but is also used for other processes.

So plants use water in photosynthesis and they combine water with carbon dioxide in order to make their biomass, in order to make carbohydrates, proteins, and fats.

So plants don't just need it to make up the cytoplasm within their cells, they also need it to build all of the rest of their bodies as well.

Plants and animals also use water to transport dissolved substances around their bodies.

So plants have veins which run up through the stem into the leaves and this is where water is transported through the plant.

And, of course, animals have veins as well, and blood is used to transport dissolved substances.

And a large portion, at least 50% of blood, is made up of water as well.

Now, water is found everywhere.

Water is found in the atmosphere present as water vapour, so in a gaseous state, and also as liquid water that we see as clouds.

It's found as solid water in the form of snow and ice.

It's found as liquid water in rivers and lakes.

It's also found within living organisms, as I've just said.

Water is also found within the soil and in the ground.

So in underground caves, that sort of thing as well.

And it's also found in the oceans.

So water, as I said, is found everywhere and in solid, liquid, and gas states.

Now, water is moved between all of these different locations by various different processes which form the water cycle.

Now, we're gonna have a look at some of the important parts of the water cycle that are related to trees and are impacted by deforestation.

So some of the important stages in the water cycle are that water in the atmosphere is deposited on the ground through the process of precipitation.

So this is falling rain, snow, hale, sleet, all of these are precipitation.

And this is where water vapour, which has condensed into liquid water, has become heavy enough to fall back down to Earth.

So that's one important stage.

Another important stage is the runoff of surface water from higher ground to lower ground and eventually making its way through into the oceans.

Now, some of the water which is moving through rivers and is present within lakes, for instance, moves into the ground itself and percolates, so filters its way through the soil and through the underground rock structures.

Water also reenters the atmosphere via plants through a process called transpiration via the leaves.

So what I'd like you to do is to complete the sentences using only the words precipitation, runoff, and transpiration.

So I'll give you five seconds to decide.

Okay, let's see what you put.

Water vapour in the atmosphere falls to Earth as precipitation.

Surface runoff moves water to lower ground and eventually into the oceans.

Some water is taken up by plants and released into the atmosphere from their leaves by transpiration.

Well done if you got all three words in the correct locations.

So let's now have a look at how deforestation affects the water cycle.

So on the left there, the diagram shows the water cycle with the forest present.

And we've just looked at that and seen how trees and other plants contribute to the water cycle by releasing water into the atmosphere via their leaves in this process called transpiration.

But if we remove those trees, what happens? Have a look at the diagram on the right.

Which process has been lost? Well, you can see that this process of transpiration from plants has gone because the plants are no longer there, the trees have been cut down and burnt.

Now, losing trees and other plants, and therefore losing this process of transpiration, has many knock-on negative effects.

As less water is being moved into the atmosphere, the loss of transpiration leads to lower levels of precipitation over low lands such as agricultural land.

And this means that those areas become drier because less rain is falling.

And this means that it makes it harder for crops to grow because the ground is drier.

There's less water.

And so farmers will have to irrigate, they'll have to water their crops instead of them being watered naturally by rain because the rain won't be falling as often.

We can also see how the area of water on the land has increased.

In other words, flooding has happened.

And this means that agricultural land where the crops are growing is being flooded and also likely to impact on homes and other buildings which are built nearby, so flooding of low land increases.

And you may well have seen lots of headlines about that over the last year or so as flooding has become more frequent in both the UK and abroad.

Other impacts of cutting down the trees involve how the trees interact with the rest of their environment.

So trees have enormous roots.

If you imagine the size of the canopy, the leaves of the tree, they have at least the same size underground as well of root systems. And what this does is bind the soil together and keep it in place and secure.

And so when we cut down trees, we stop those root systems from functioning because they die or we dig them up and therefore the soil becomes loose.

And so the good quality soil, which is quite light and free in nature, gets washed away by the flooding that then happens on the land.

And so more good quality soil gets washed into the oceans, perhaps via rivers, but ultimately into the oceans.

Also, and we can see that with the dotted pink arrow, that because the trees have been cut down and the good quality soil has been washed away, what's left is poorer quality soil.

And by that we mean less absorbent soil.

It's often much denser and it's often made of materials like clay, which actually don't absorb water very well at all.

And so instead of the soil being able to absorb water and the trees actively encouraging that through their root systems because that's how they absorb water, none of those processes happen.

The good quality soil has been washed away and poor quality soil, which cannot absorb as much water, is left behind.

And this soil doesn't absorb water very well, water runoff increases and makes flooding worse.

So cutting down trees, deforestation, has many different negative knock-on effects.

But as we've already seen in the carbon cycle section of this lesson, we can protect and restore forests.

And if we do that, then we will restore trees, and therefore return them back into the water cycle and that will improve the quality of soil, improve the quality of land, reduce the amount of flooding that is taking place, increase the amount of rainfall that is happening over low land, and therefore altogether improve food security.

But we have to do that.

We have to protect forest to prevent it from being deforested.

And we have to reforest, we have to plant those trees in order to restore forest land.

So true or false? Deforestation increases transpiration.

Okay, so you should have said that that is false, but why is it false? So you should have said it is false because deforestation removes trees and other plants, and trees and other plants are taking up water through their roots and releasing it into the atmosphere from their leaves by this process of transpiration.

And therefore, if we have fewer trees, we have less transpiration.

Well done if you got that correct.

We've seen how reforestation and preventing deforestation is really important, and some people protest against deforestation in order to save forests.

And you can see some of those banners campaigning to protect this bit of forest.

So what I would like you to do is to explain why reducing deforestation will help to limit climate change, limit flooding, and support our food security.

So pause the video and come back to me when you've given that a good amount of thought.

Okay, let's check your work.

So how have you explained the positive impact of reducing deforestation? Well, reducing deforestation, you may have said, will maintain the role of forests in the carbon cycle.

And this means they will absorb carbon from the atmosphere, which will remove some of the emissions of greenhouse gases that we are putting into the atmosphere and this will help to limit climate change.

You should have also mentioned how reducing deforestation will help to maintain the role of forests in the water cycle.

And this is important because trees absorb water through their roots and release it into the atmosphere through transpiration.

And the presence, therefore, of trees will reduce flooding and help to maintain soil quality, which protects against agricultural land from flooding.

So well done if you mentioned all of those points.

Do add to your work if you need to and good work.

Okay, we've reached the end of our lesson.

And in our lesson today, we have seen how deforestation disrupts the carbon cycle because less carbon dioxide is absorbed from the atmosphere for photosynthesis.

We've also seen that carbon dioxide is a greenhouse gas that enhances the greenhouse effect, and this contributes to climate change.

We've seen also how deforestation disrupts the water cycle because less water is absorbed and moved into the atmosphere through transpiration by plants.

And more surface runoff of water increases flooding and puts food security at risk.

So reforestation and legal protection for forests is really important to prevent deforestation and to regrow forests, and therefore to help maintain the role of forests in both the carbon and the water cycles.

So I hope you found that interesting, lots of things to think about there.

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

Bye.