Lesson video

Hello, geographers.

My name's Mrs. Hormigo and I'm looking forward to teaching you today.

I hope you are going to enjoy the lesson and learn lots.

Let's get started.

Today's lesson looks at the causes of climate change.

So by the end of the lesson, you will understand the natural and human causes of climate change.

There are three keywords for today's lesson.

Milankovitch cycles: natural changes in Earth's orbit and tilt over thousands of years that influence solar energy and Earth's climate.

Greenhouse gas: a gas that traps heat in the atmosphere, contributing to Earth's warming, for example, CO2 or carbon dioxide and methane.

Enhanced greenhouse effect: the increased concentration of greenhouse gases in the atmosphere due to human activities, leading to global warming.

There are two learning cycles for today's lesson, What are the natural causes of climate change? and What are the human causes of climate change? Let's get started on the first, natural causes.

Natural causes of climate change are factors and processes that influence the Earth's climate without any human influence, and they include Milankovitch cycles, solar output from the Sun, volcanic activity and asteroid collisions.

Milankovitch cycles.

Milankovitch, a Serbian scientist, studied the Earth's orbit and he found that natural changes in the Earth's movement and position in space have effects on climate.

He identified three main cycles, eccentricity, which is the shape of the Earth's orbit as it travels around the Sun, axial tilt, so the tilt of the Earth's axis, and precession, the wobble of the Earth's axis.

Eccentricity.

The Earth's path around the Sun changes from being more circular to slightly elliptical and back again, and this is over a period of about 100,000 years.

So as we can see in this first diagram on the left, colder periods, like ice ages, are more likely during a more circular orbit because it reduces seasonal extremes.

The distance of the Earth from the Sun doesn't change.

When the orbit is more elliptical, the distance from the Sun varies more, which increases seasonal differences.

Axial tilt.

The Earth spins on its axis, and it's currently tilted at 23.

5 degrees.

Over a period of 41,000 years, that tilt moves between 21.

5 and 24.

5 and the greater the tilt, the higher the global average temperature is.

And precession, this describes the natural wobble of Earth, and a complete wobble cycle takes 26,000 years.

We are likening it to a spinning top that you may have played with as a child.

As it spins, it also wobbles on its axis.

An axial precession makes seasonal contrasts more extreme in one hemisphere and less extreme in the other.

Now a check for you.

Name the three Milankovitch cycles that naturally affect Earth's climate over thousands of years.

Pause the video, and come back when you have your answers.

Did you get it correct? A, was eccentricity, the orbit around the Sun, B, axial tilt, and C, precession.

Well done if you did.

Let's have a look now at solar output.

The amount of energy put out by the Sun changes in cycles, and that's linked to sunspots.

Now sunspots are dark patches on the Earth's, Sun's surface, sorry, caused by strong magnetic fields, and they're linked to solar flares.

If there are more sunspots, there's a greater solar output, which leads to a warming of the Earth's surface.

When there are fewer sunspots, there's reduced solar outputs, and so temperatures are slightly cooler.

This happens on an 11-year cycle.

The number of sunspots rises and falls over this period of time.

Volcanic activity.

Large eruptions release ash and dust high into the atmosphere, and the particles can block out sunlight, causing short-term cooling, which we call a volcanic winter.

They also release sulphur dioxide, which forms sulphate aerosols, and these aerosols in the stratosphere reflect sunlight back into space, which further cools the Earth.

Asteroid collisions are similar in this sense.

They cause a cooling impact.

A large impact releases masses of dust, ash, and gases that block any incoming sunlight.

Right, a check for you.

Which of these statements are correct? Read them carefully.

A, The number of sunspots rises and falls over an 11-year cycle, B, Ash and dust released by a large volcanic eruption can cause a warming effect on Earth, C, Asteroid collisions can cause a cooling effect due to the release of dust, ash, and gases that block incoming sunlight.

Pause the video, and come back when you've decided.

Did you say A and C? If so, well done.

B is not correct because ash and dust released by large volcanic eruptions would cause a cooling effect on Earth as they reflect the sunlight back.

First task for you now.

Can you complete this table summarising the natural causes of climate change? As you can see, the first row has been done for you, the cause being Milankovitch cycles.

We've got an explanation saying, natural changes in Earth's movement and position in space which affect climate, eccentricity, axial tilt, and precession being the main three cycles.

And, this affects the climate because it affects the amount of solar energy the Earth receives, affecting timings and seasons of Earth climate.

Can you have a go at filling out the same table for solar output and volcanic activity? Come back when you've got your table complete.

Did your table look something like this? So for solar output, the explanation could have been similar to, changes in the Sun's energy output linked to an 11-year sunspot cycle.

And the impact this has is that more Sun spots increase solar energy warming Earth.

Fewer Sunspots are linked to cooling, and for volcanic activity, releases of ash and dust into the atmosphere by an eruption, and sulphur dioxide is released, which forms aerosols.

And the impact this has is that it blocks sunlight, causing temporary cooling, and the aerosols reflect sunlight back into space, further cooling Earth.

Well done if you've got a similar set of answers in your table.

Let's move on now to human causes of climate change.

The greenhouse effect is a natural process that warms Earth's surface.

Greenhouse gases in Earth's atmosphere trap heat from the Sun, and we can see here on this diagram.

We have solar radiation from the Sun warming the Earth's surface.

The Earth's surface then radiates this heat as infrared radiation back towards the atmosphere.

Greenhouse gases that are naturally occurring in the atmosphere absorb some of this infrared radiation, trapping it.

The trapped heat is reradiated back towards Earth, and some of the heat escapes, and this process is essential for supporting life on Earth.

Naturally occurring greenhouse gases that we find in the Earth's atmosphere include water vapour, carbon dioxide, methane, and nitrous oxide.

And some of the sources of these gases are evaporation from oceans, lakes, and rivers, volcanic eruptions, oceans, transpiration from plants, and respiration of plants and animals.

We can see here on this graph, annual carbon dioxide emissions between 1750 and 2022.

Human activities release additional greenhouse gases into the atmosphere, in particular, carbon dioxide.

And this has increased the amount of heat trapped, which leadS to the enhanced greenhouse effect.

We see by looking at that graph that there's been a steep rise in the amount of CO2 emissions from 1950 onwards, and that's linked directly to an increase in human activities that are producing it.

So the enhanced greenhouse effect, it enhances or it adds to the natural greenhouse effect.

So human activities, such as burning fossil fuels, increase the concentration of greenhouse gases in the atmosphere, and this interferes.

A higher concentration of these greenhouse gases means less heat escapes, and more heat is trapped in the atmosphere, and more heat trapped in the atmosphere leads to a rise in global temperatures, which we know as global warming.

True or false? The greenhouse effect is a natural process.

Have you been listening? Can you decide whether that is true or false? Come back when you have your answer.

I hope you said true, but why is it true? Pause the video, and discuss with the person next to you why you said true.

I'm sure your discussion said something similar to this.

The greenhouse effect is a natural process that warms Earth's surface.

It occurs when greenhouse gases in Earth's atmosphere trap heat from the Sun.

Human activities have increased the concentration of greenhouse gases in the atmosphere, causing the non-natural enhanced greenhouse effect.

Well done.

So the enhanced greenhouse effect has led to an increase in global temperatures, as we've said, global warming.

And we can see here evidence on this graph showing annual temperature anomaly.

And you can see that between 1880 and 2020, we've seen a gradual or a quite a quick increase in global temperatures.

These are the main greenhouse gases released by human activities.

So we've got the greenhouse gas, and the human activity that is releasing it.

Carbon dioxide comes mainly from the burning of fossil fuels, vehicles, deforestation.

Methane is released by livestock, particularly cows, and during rice cultivation.

Nitrous oxide is found from artificial fertilisers, burning fossil fuels, and other industrial processes, and chlorofluorocarbons, known as CFCs, come from aerosols, refrigeration units, and air conditioning.

Can you name three of the main greenhouse gases released by human activity that are contributing to the enhanced greenhouse effect? Pause the video, and come back when you have three.

Did you manage to sat carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons, any of those, any three of those four? The enhanced greenhouse effect causes global warming.

Global warming causes climate change because climate patterns are driven by heat energy.

Global warming is caused by many human activities, but especially these three, burning of fossil fuels, deforestation, and agriculture, and we're going to look at these in a little bit more detail now.

Burning of fossil fuels, so fossil fuels are relied on for generating electricity across the world, but also for transportation and industry.

They're mostly made of carbon, and burning fossil fuels, such as coal, oil, and natural gas, releases large amounts of carbon dioxide, as well as some methane and nitrous oxide.

And we know that carbon dioxide is the main contributor to the enhanced greenhouse effect and therefore, to global warming.

Deforestation, so trees absorb CO2 from the atmosphere during photosynthesis.

When forests are cleared, there are less trees that can take in that CO2, so more of it stays in the atmosphere.

Trees also provide a store for carbon in their trunks and their branches and roots.

And when trees are cut down or burned, the carbon is released, and it is released as carbon dioxide, which increases greenhouse gas levels.

Agriculture, so by clearing land for grazing and for crops via deforestation, it reduces the absorption of CO2.

And this is happening more and more as our population increases and the pressure on land and supply of food increases too.

Increases in meat, dairy, and rice production mean there are more methane emissions, and producing fertilisers and pesticides relies on fossil fuels, and as we've said previously, releases nitrous oxide.

Okay, check for you now.

Can you complete this spider diagram by adding the missing labels? So look carefully at the pictures and think about what we've been discussing.

Pause the video, and come back when you have your answer.

Did you say the main human causes of climate change are the activities agriculture, deforestation, and burning fossil fuels, which all release greenhouse gases into the atmosphere? Task B, can you add annotations to this diagram to explain the natural greenhouse effect? And for question number 2, how are human activities causing the enhanced greenhouse effect? Pause the video, and come back when you've completed these two questions.

So did your annotations look something similar to this? Solar radiation from the Sun warms the Earth's surface.

The Earth's surface then radiates this heat back as infrared radiation back towards the atmosphere.

Greenhouse gases in the atmosphere absorb some of this infrared radiation, trapping the heat.

This trapped heat is reradiated back towards Earth, and some heat escapes.

So this is the natural greenhouse effect, and it's absolutely essential for life on Earth.

Question number 2, how are human activities causing the enhanced greenhouse effect? Your answers may have included points like this.

Human activities, such as burning fossil fuels and deforestation, increase the concentration of greenhouse gases in the atmosphere.

More heat trapped in the atmosphere leads to a rise in global temperatures, global warming.

A higher concentration of greenhouse gases means less heat escapes and more heat is trapped in the atmosphere.

Well done if your answer was similar to this.

Lots of points to be made there, so lots to think about.

Well done.

Right, we've got to the end of the lesson.

Let's have a little look at the summary.

Natural factors have caused climate change over millions of years.

These include Milankovitch cycles, changes in solar outputs, sunspots, and volcanic activity.

The greenhouse effect is also a natural process that warms Earth's surface.

It occurs when greenhouse gases in Earth's atmosphere trap heat received from the Sun.

Human activities, such as deforestation, burning fossil fuels and agriculture, are increasing the concentration of greenhouse gases, and this is known as the enhanced greenhouse effect, and it causes global warming.

The rise in global temperatures over the last century and the climate change caused by global warming is the result of human activities.

Excellent.

Well done.

I hope you can now confidently discuss natural and human causes of climate change.

Well done today.

I look forward to seeing you again soon.