Lesson video

Hi, geographers.

My name's Miss Hoggett's and I'm really excited you are here to learn some geography with me today.

I'm sure if you try your best, you're going to be absolutely fantastic.

Don't worry too much if you haven't studied this topic before.

I'm here to help you every step of the way.

The "Past climate change," and this sits within the unit, "Weather and climate: how do they vary?" Our learning outcome for today is that I can describe different types of evidence of past climate change.

We have a number of keywords that are going to help us through today's lesson.

Reliability, global warming, evidence, and climate change.

Reliability, how accurate or able to be trusted something is considered to be.

Global warming, an increase in Earth's average temperature over a long period of time.

Evidence, a fact or piece of information that helps to prove that something is true or not.

Climate change, large-scale and long-term change in the planet's climate.

So reliability, global warming, evidence, and climate change are going to help us through today's lesson.

Now, today's lesson is split into two learning cycles.

What is climate change? And what evidence do we have of past climate change? So we're going to start with our first one now.

What is climate change? Now, climate is the average weather conditions in a place, taken over a long period of time.

This is different to climate change, which refers to the long-term change in the planet's climate.

And that's different again to global warming, which is the increase in the Earth's average temperature over a long period of time.

Global warming is different to global cooling because that would be a decrease in the Earth's average temperature over a long period of time.

Climate change can include both global warming and global cooling.

On the slides, we can see a graph titled "Change in the average global temperature over the past 450,000 years." On this graph, we can see that our line decreases and increases over time.

And we can also see that those decreases and increases are labelled glacial and interglacial.

Now, to me, glacial sounds like glacier, which is a frozen river of ice.

So I could assume that those time periods were probably really cold, which means our interglacials must be warmer.

We can also see that from the y-axis on the left-hand side, which says we are labelling temperature in degrees Celsius.

So as we can see, glacial periods were much colder and interglacial periods were much warmer.

Now, this graph is showing over time, and our x-axis confirms that because it shows that the graph covers 450,000 years.

So we can see that Earth climate has varied naturally over time.

Let's check your understanding of that.

So climate change has always been about global warming, true or false? I'll give you a moment, pause the video and have a go at this question.

Well done if you said false.

Climate change's large-scale and long-term change in the planet's climate.

Earth has experienced periods of global cooling, so glacials, as well as periods of global warming, which are our interglacials.

Well done for the hard work you're putting in so far.

Sam says, "So climate change includes global warming, and global cooling?" And Jun says, "Yes, that's correct." Well done, Sam.

Now, people often confuse climate change with global warming, as they use the terms interchangeably.

You may have seen some of these terms in the news and got a little bit confused yourself, and that's okay.

People tend to focus on immediate effects, so things that are happening right now, such as hot summers and melting ice.

It's easier to connect with the idea of global warming, because that's what we can feel happening right now, even though it's only part of the picture.

So even though we can see an image of some icy waters there, actually that's not something I've ever experienced before.

So I relate more to the city where we can see the really high temperatures and that's why it's easy for people to get confused.

Understanding.

So Lucas' statement is not accurate.

What two words could he replace to make the statement accurate? So Lucas says, "Climate change is when the temperature of the world rises over a long period of time." Have a think.

What two words would you need to replace in order to make that correct? Pause the video and have a think.

Climate change is wrong there.

Actually, the right answer would be global warming.

So it would read.

Global warming is when the temperature of the world rises over a long period of time.

Well done, geographers.

So we're now going to practise what you've learned so far.

The first thing I'd like you to do for this practise task is annotate the graph to show how climate has changed over the last 400,000 years.

Then, for part two, I'd like you to explain the difference between global warming and climate change.

Pause the video and have a go at completing this practise task.

Well done for giving that a go.

Let's have a look at what your answers may have included.

So for our first task and I take the graph to show how climate has changed over the last 400,000 years, we can see that we have glacial periods, which were much colder, and then we have interglacial periods, which were much warmer.

Well done if you've got those two points.

For our second task, we needed to explain the difference between global warming and climate change.

So you may have said, "Climate change refers to the long-term change in the planet's climate, whereas global warming is the increase in the Earth's average temperature over a long period of time." Well done if you've got something to that effect, you're doing a fantastic job and we've now finished learning cycle one.

So we are ready to move on to learning cycle two.

What evidence do we have of past climate change? We can use scientific instruments to measure the weather.

This data means we can track any change in average weather or climate over time.

Now, when we say instruments, we are not talking about things like guitars and pianos, but we're talking about scientific equipment like thermometers and anemometers, which help us to understand how the weather has changed.

Since 1914, the Met office has recorded reliable climate change data using weather stations, satellites, ocean buoys, and other equipment.

But what that doesn't do is help us to understand where all the data for this graph came from and the data for 450,000 years ago in particular, because 1914 is just over 100 years ago.

So pause the video and have a think.

Where do you think the data for this graph came from? So did you suggest evidence? Now, we can use evidence as this is a fact or piece of information that helps us to prove that something is or is not true.

Alex says, "Detectives must gather evidence to prove that a crime took place and discover whodunit." Laura says, "Oh, but we can't interview a woolly mammoth!" And she's absolutely spot on.

So yes, we do need to find evidence, but we need to look for evidence in lots of different places.

Thankfully, there are lots of pieces of evidence that the world's climate was different in the past.

They include things like fossils, physical landscapes, ice cores, historical documents, and tree rings.

So we are going to have a look at these in a little bit more detail to understand how they can provide us evidence for climate change.

So we're going to start with fossils.

Fossils help us to understand what the climate was like in the past, as they show what kinds of plants and animals lived in different places at different times.

On the screen, we can see some images of different plants and animal fossils.

And we would expect them to be found in a place that matches the type of climate that they need to survive.

But that's not always the case because tropical plants and animals have been found as fossils in cold places that could tell us that the climate used to be much warmer.

Such as these cycads, tropical plant fossils, which were found in the Arctic.

And these alligator-like species, their fossils were found in the Arctic too.

So either they've moved or the climate in the Arctic used to be much warmer.

Now, fossil records provide us with an incomplete picture of species that used to live in the distant past.

Because the conditions needed for their materials to be preserved are very specific.

So that means this is a limitation of that form of evidence of climate change, and it makes them much less reliable.

Let's check your understanding so far.

True or false? Fossils are highly reliable pieces of evidence for climate change.

Pause the video and have a go at this, check for understanding.

Well done if you said false.

Fossil records provide us with an incomplete picture of species that lived in the distant past because the conditions needed for plant or animal material to be preserved are very specific.

Well done, geographers.

You're doing a fantastic job.

Our next piece of evidence is physical landscapes.

Now, physical landscapes can help us to understand how climate has changed.

For example, the Lake District's landscape was shaped by ice.

We can see that in this image.

The Lake District has distinct U-shaped valleys, so that means the valley there is shaped like a U as you can see in the photo.

Now, these were created by the movement of glaciers.

Glaciers are frozen rivers of ice, so they bulldozed through the landscape and create that distinctive U-shape.

This tells us that these areas were once much colder.

As the climate warmed, the glaciers melted.

So I wouldn't expect to see a frozen river of ice today in the Lake District, but I can see that the landscape was previously shaped by them.

Let's check your understanding.

What does the shape of the U-shaped valley in the Lake District, tell us about its past climate? Is it a, it was once much warmer, b, it was once much colder, c, the area has always been the same temperature, or d, the valleys were formed by rivers, not ice? Pause the video and have a go at completing this check for understanding.

b, it was once much colder.

We wouldn't expect glaciers today because the temperature is too warm.

So therefore, if glaciers existed in the Lake District in the past, we know it must have been much colder.

Fab work.

Our next example of evidence is ice cores.

Now, ice cores are like time capsules for the Earth's climate.

Scientists use drills to extract ice from deep within the sheets of Greenland and Antarctica.

As you can see in the image, we've got that huge drill there and it's taken out that cylinder of ice.

Now, they provide us with a complete record of the Earth's climate, going back at least 800,000 years.

Ice cores contained bubbles of air trapped when the ice was formed.

The oldest ice is at the bottom.

Different chemical elements in the ice form differently in warmer or colder times.

So the air bubbles tell us how much carbon dioxide was in the atmosphere at different times, in chronological order.

It's quite clever, really.

So those air bubbles can give us a good understanding of what the climates used to be like up to 800,000 years ago.

Now, ice cores from Greenland and Antarctica reveal that Earth has had sudden periods of warming and cooling in the last 400,000 years.

By studying these cores, scientists have been able to link temperature change to change in the level of carbon dioxide in the atmosphere.

So it gives us a really good understanding of how climate has changed over time.

Let's check your understanding.

True or false? Ice cores provide information about the climate of the past 800,000 years, or more.

Pause the video and have a go at completing that question.

Ice cores provide us with the complete records of the Earth's climate, going back at least 800,000 years.

Now because the air bubbles have been formed naturally, there are really reliable form of evidence for climate change, much more reliable than our fossils, which we know could have been moved or they could have been affected by the conditions.

Our next piece of evidence are historical documents.

Now, historical documents can be used as evidence for climate change, such as diary entries, photographs, and paintings, or because they're representations of past climate.

We can see an image showing a Frost Fair on the frozen River Thames in 1855.

What does this image suggest about London's past temperature? Pause the video and tell the person next to you.

Well done if you suggested that actually it means the temperature used to be much colder.

I wouldn't expect to see a Frost Fair on the River Thames nowadays because it's too warm, it wouldn't freeze.

So the fact it was frozen and the ice was thick enough for a Frost Fair, means that it must have been much colder.

The reliability of historical documents is often questioned because they present the view of one person and their view may be biassed or inaccurate.

It may also be based on hearsay, if they were not actually there at the time.

Sofia says, "Yeah, an artist are creative people, so their work may not be entirely based on fact!" And she's absolutely spot on.

So we always have to consider that they may have been open to interpretation and therefore, may not be 100% reliable.

Let's check your understanding.

So which of the following is an example of a historical document that could provide evidence of past climates? a, a scientific graph of temperatures from 2020, b, a weather forecast for the next week, or c, a diary entry from 1855.

Pause the video and have a go at completing that task.

Well done, geographers.

Let's check your answer.

So the answer is c, a diary entry from 1855.

A weather forecast for the next week and a scientific graph from 2020 wouldn't be examples of historical documents.

So well done if you got that correct.

So our last piece of evidence for climate change is tree rings and they can provide us evidence of climate change.

When I'm talking about tree rings, I'm talking about the circles you can see in their trunks.

Now, trees grow differently depending on the climatic conditions each year.

A cross section of a tree trunk has rings that allow us to compare that growth each year.

Narrow rings form during cold and dry years when the growth is slower.

So we can see that in the left-hand side picture, they're really close together.

Whereas wide rings form during warm, wet years when trees grow faster.

And we can see in the second image, we've got rings that are much further apart from one another.

So it tells us a lot about the climate.

Let's check your understanding of that.

So true or false? Tree rings provide evidence of climate change because the width of each annual ring tells us how wet or cold it was.

Pause the video and have a go at answering that question.

Trees grow faster when the weather is warmer and wetter.

Spot on, geographers, what a great end to that evidence.

So we are now going to practise what you've learned so far.

So you've got two parts to this practise task.

Part one, what can these pieces of evidence tell us about past climate change? Write a sentence or two about each.

So you have an image, which is a historic painting for a, and then b, you have an ice core.

And then part two of this practise task, which of these pieces of evidence is more reliable? Explain your answer using the following words, accurate, temperature, science, art, fact, and opinion.

Pause the video and have a go at completing this practise task.

Well done for giving that are really good go, geographers.

Let's have a look and see what your answers may have included.

Historical paintings can tell us about the weather in a particular place at a point in history, for example, when it was cold, the River Thames froze.

And ice cores provide information about how the temperature has changed over time.

This is because certain chemical elements form differently under warmer or colder conditions.

For part two, your answer may include, ice cores are more reliable than historical paintings for studying past climate.

Cores give us accurate data on what the Earth's atmosphere was like when the ice formed.

From the sequence of layers within each core, we can see how the temperature changed over time.

Historical paintings may be less reliable.

They are creative works of art and may include things that did not actually happen.

Also, a painting may be created much later than the actual weather event.

So we can see that the reliability of different pieces of evidence can change depending on where they've come from.

You've done a brilliant job today, geographers.

So to summarise, climate change is the large-scale and long-term shift in the planet's climate.

The Earth's climate has varied naturally and continuously over time.

Over the past 400,000 years, climate change involved periods of global cooling, so glacials, as well as periods of global warming, interglacials.

And ice cores, fossils, tree rings, and historical documents and paintings, all provide us with evidence of climate change.

Thank you for working really, really hard today, geographers.

You've been brilliant and I look forward to seeing you in our next lesson.