Lesson video

Hello, geographers, My name's Mrs. Hormigo, and I'm going to be teaching you today.

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

Let's get started.

Today's lesson looks at climate change during the Quaternary Period, we're going to look at how the climate has changed and what evidence we have for this.

So by the end of the lesson, you'll be able to understand evidence for climate change in the Quaternary Period.

There are three keywords for today's lesson: Quaternary Period, which is the period of geological time from 2.

6 million years ago to the present.

Climate change, which is a long term change in Earth's climate patterns, and ice core: a cylinder of ice extracted from an ice sheet or glassier, which is used to analyse past climate conditions.

There are two parts to today's lesson: "How has the climate changed in the past?" and "What evidence is there for climate change?" Let's get started on the first learning cycle.

So the Earth, it's estimated to be 4.

6 billion years old and its history has been divided into eras, periods and epochs through a geological timescale.

And we have an image there detailing this geological timescale.

The Quaternary Period began 2.

6 million years ago and it extends to the present day.

So it's what we are currently in.

It's part of the Cenozoic era.

So temperatures have changed over time relative to today's average temperature.

We have a graph here detailing it.

The red line shows today's average temperature, and the fluctuating black line shows how temperature has changed over the last 5.

5 million years.

And we can see that before the Quaternary Period, the Earth climate was warmer and more stable.

There were less fluctuations and it sits mostly above today's average temperature.

During the Quaternary Period, we've seen major temperature fluctuations, but overall there's been a gradual decrease in temperature, and those changes have all had natural causes historically.

Here we have a graph showing temperature change over a shorter time period, so it looks at it in a little bit more detail.

This shows how the temperature has changed from the average over the last 420,000 years.

It shows temperature anomaly and also CO2 concentration, and we can see that there is a relationship between the two.

Higher temperatures are associated with higher CO2 concentrations.

This graph shows that the Quaternary Period has seen cyclical changes between cold glacial periods, and we can see here the most recent glacial period, and warmer interglacial periods.

And again, current interglacial period.

These cycles last about 100,000 years due to natural variations in the Earth's orbit.

And that's something that we'll come to later in the unit.

Check for you now.

Does point A indicate a glacial or interglacial period? So think carefully what those terms mean and what it means for the temperature.

Pause the video and come back when you're ready.

Hopefully you said it's an interglacial period, so it's a time when temperatures are higher than the average.

During glacial periods, global temperatures dropped significantly and ice sheets expanded across large areas and that included much of Europe and North America.

They were covered in ice.

Sea levels fell as the water froze and was locked in glaciers.

And this exposed what we call land bridges.

So you could move between Britain and mainland Europe, for example.

Here's an example of an ice sheet in northern North America.

The Laurentide Ice Sheet covered much of Canada and the northern United States during the last glacial maximums, the last ice age, 20,000 years ago.

And in parts, it was four kilometres thick.

So you can see there that white area on the map shows the Laurentide Ice Sheet.

Interglacial periods are the shorter, warmer periods between the glacial periods and they are lasting around 10 to 15,000 years.

During these interglacials, ice sheets retreat, so they melt, sea levels rise and ecosystems have to adapt to warmer climates.

So there massive shifts in the environment.

Another check for you now.

Which of these statements are true? A: The Quaternary Period started 2.

6 million years ago.

B: Before the Quaternary Period, global temperatures were generally higher than today.

C: During the Quaternary Period there has been a general increase in temperatures.

Pause the video and come back when you know the answers.

Did you choose A and B? If so, well done.

The Quaternary Period started 2.

6 million years ago and global temperatures were generally higher than today before the Quaternary Period.

During the Quaternary Period, there's been a general decrease in temperatures.

The most recent glacial period occurred between 120,000 and 11,500 years ago.

Since then, we have been in an interglacial period known as the Holocene.

So temperatures have risen and ice sheets have retreated.

So as we've said, most of the Quaternary Period saw a gradual decrease in temperatures.

However, the past few decades have seen rapidly warming temperatures, and you can see here a graph with a much shorter timescale.

So between 1880 and 2023, and this shows a rapid increase in temperatures.

It's risen from minus 0.

17 degrees Celsius up to 1.

17 degrees Celsius.

So that's a rise of 1.

17 degrees Celsius since 1880.

And the 10 most recent years are the warmest on record.

So global temperatures are increasing.

Check for you now.

This graph shows how global average temperatures have varied compared to the average in 1880.

Which statement best describes the trend shown in this graph? Let's read them carefully.

A: the average global temperature has increased every year since 1880.

Global temperatures go up and down without any clear trend.

Global temperatures have increased rapidly since the 1970s.

Pause the video and think which is the correct statement.

Hopefully you ticked C.

Global temperatures have increased rapidly since the 1970s.

So we can see that there are fluctuations.

The graph doesn't just go up in a straight line, but since the 1970s, there's been a steeper increase in temperatures on the graph.

Right, onto our first task.

There's an image of this graph that we've been looking at, showing glacial and interglacial periods.

Can you complete the annotations on this graph to describe significant temperature changes over the last 400,000 years? And Izzy says, "The key terms I should be using in my annotations are glacial and interglacial periods." So use the boxes and the arrows and see if you can add the annotations.

Pause the video and come back when you've completed it.

Your graph and its annotations should look something like this.

Interglacial periods pointing to that arrow on the top left.

Shorter, warmer periods lasting around 10 to 15,000 years.

The bottom arrow on the left pointing to an area where we've got a glacial period, significant drop in global temperatures.

And on the right-hand side, an interglacial period, the Holocene, following the end of the last glacial period.

And you might have mentioned as well that that's the period that we are currently in.

Well done if you've had a good go at that task.

Right, let's move on to the second part of the lesson.

What evidence is there for climate change? How do we know about all these changes in temperature? So scientific data from natural sources and modern technology, such as satellites, provide both historical and recent evidence of changing climates.

Humans were not around for all of these temperature changes, so we need to look to natural sources to find out some information.

The historical evidence that we use are ice cores, fossil records, tree rings and diaries and paintings, and the more recent evidence that is useful, are global temperature records, melting ice and sea level rise.

We're gonna look at each of these in a little bit more detail.

Scientists have used this evidence to show how climates have changed over the Quaternary Period and to measure modern changes.

Let's look first at ice cores.

We've got an image here of somebody handling an ice core.

So in polar regions, layers of snow compress into ice over time, preserving the air and the water molecules that were present at that moment in time.

Scientists can then analyse these trapped air and water molecules and it helps them to calculate the temperature of the atmosphere when the snow fell.

So they look for different concentrations of oxygen and carbon dioxide and other gases that were found naturally in the atmosphere.

And they provide data for 400,000 years of climate history.

So they are an incredibly valuable source of evidence.

Secondly, fossil records.

So fossil records allow the scientists to reconstruct climate changes over the whole Quaternary Period, so an even longer time span than the ice cores.

Using these, we can see changes in the distribution of plant and animal species that would tell us that the climate changed.

And fossilised coral reefs can indicate past sea levels and ocean temperatures as well.

So we've got a good record of land and sea temperatures.

And extinction events found in the fossil record often correlate with rapid climate changes, so we can use other sources with the fossil records in order to find more evidence to support changes to the climate.

Thirdly, the tree rings.

So we've all probably seen an image like this before, all the rings found in the trunks and the branches of a tree.

So trees can live for hundreds and even thousands of years.

So they will experience many, many different climate conditions.

And each year a tree grows, it forms a new ring, and the width of the ring indicates the climatic conditions for the year.

So if it's a wider ring, it indicates warm and wet years, and a thinner ring shows years when it was colder and drier.

And from, finally, diaries and paintings.

So these are provided by people, so it doesn't provide records from as long ago.

The diaries provide a written record and the paintings provide a visual depiction, and it's based on a human perspective.

So people's opinion and interpretation of what the weather was like at that time.

So we have to remember it's subjective and it's useful when it can be used in support of scientific data, but it's not as reliable as the scientific data.

Right, true or false for you here.

Diaries and paintings are the most important evidence of climate change.

True or false? Pause the video and make your decision.

Hopefully you said false, but can you tell me why you said that? Pause the video and think of your reason why.

Hopefully you said something similar to this: "They are only based on human observations and should therefore be used alongside the scientific evidence found in ice cores and tree rings." Well done.

We move on to the more recent evidence, starting with global temperature records.

So accurate weather records have been collected around the world for about 170 years, and the current temperatures can be compared to the long-term averages.

And this map here shows temperature differences around the world based on an average between 1981 and 2010.

And these were temperature anomalies for 2020.

So we can see here that the majority of the Earth was warmer in 2020 than the 30 year average.

So the map is mostly in the red colours.

And this area, particularly in Northern Asia extending into the Arctic and parts of Eastern Europe, were much warmer.

Melting glaciers.

This image here shows a glacier that is retreating.

We can see it, it's shrinking, it's getting smaller, and that's a clear sign of long-term climate change.

This is in Tibet, and as higher temperatures are causing ice to melt, the glassier are starting to retreat quite quickly as there's not enough snowfall to replace it.

Sea level rise.

So rising sea levels are evidence of climate change because they're caused by higher global temperatures, which melts the ice sheets and the glaciers, contributing water to the oceans, as well as thermal expansion.

So as the oceans themselves get warmer, the water molecules expand and they take up a greater volume.

And we can see here looking at this map that there is a large proportion of the world showing a high or a positive regional mean sea level change.

We can see here they've highlighted areas such as small island developing states, coastal mega cities, and delta regions that are particularly prone to the problems of sea level rise.

Check for you now.

Describe what evidence this map provides for climate change.

Pause the video and come back when you have an answer.

I'm sure you will have said something similar to: "This map shows sea levels are rising globally, which is linked to global temperature increases." If so, well done.

Right.

Let's move on to our final task.

Explain three ways scientists gather evidence for climate change.

Try to include both historical and recent sources of evidence.

There's a spider diagram set up for you to complete.

Sofia says, "I'm going to explain tree rings, temperature records, and ice cores." So we've got a mix of historical and recent sources of evidence.

Pause the video and have a go.

Come back when you're ready.

Let's have a look-see.

Your answers could have included this: Tree rings.

As a tree grows, it forms rings.

These rings can be analysed.

The wider apart they are, the wetter and warmer the climate.

Global temperature records.

This allows scientists to see how current temperatures differ from the expected averages.

And ice cores.

By analysing gases trapped in the layers of ice, scientists can determine what the climate conditions were like up to 400,000 years ago.

Well done if you completed this task successfully.

Right, we're onto the summary now of the lesson.

Let's go over what we've covered.

So firstly, the Quaternary Period began 2.

6 million years ago.

The Quaternary Period has seen natural cyclical changes between glacial periods and interglacial periods.

Scientists use both historical and recent evidence to investigate climate change.

Ice cores and fossil records provide historical evidence of climate change.

Melting glassier and rising sea levels are examples of recent evidence of climate change.

And human observations of weather conditions in diaries and paintings also add to the scientific evidence.

Well done.

I hope you've understood it and you've enjoyed the lesson.

I look forward to seeing you again soon.