Lesson video

This lesson is called Human Activity and Climate Change and is from the unit Atmosphere and Changing Climate.

Hi there, I'm 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 evaluate evidence for human activity causing climate change.

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.

So in our lesson today, we're going to first of all look at the effect of human activity on climate change before we consider the certainty that we have in the climate change data.

And then we're going to consider what is a carbon footprint and how we might calculate our own.

So are you ready to start? I certainly am.

Let's go.

Now, we get our data from all around the world and temperature is one of the bits of data that is collected daily.

So temperature is measured all around the world using weather stations, weather balloons, radar, ships, buoys and satellites.

And all this data is collected from around the world.

Now the Global Historical Climatology Network daily contains records from more than 100,000 stations in 180 countries and territories.

And you can see that data plotted on the graph on the screen there.

Now this data, which is vast in its collection and goes back many, many years, more than 130 years, clearly shows how the average global temperature is increasing.

We also collect data about carbon dioxide levels in the atmosphere.

And the Mauna Loa Observatory in Hawaii has been measuring carbon dioxide levels in the atmosphere since 1958.

In fact, it was the first place to start collecting that data.

And their data clearly shows that carbon dioxide levels in the atmosphere are increasing.

Now the increase in the amount of carbon dioxide is very similar to the changes in global temperature.

So let's put those two graphs alongside each other and we can see that as atmospheric carbon dioxide levels have increased, so has average global temperatures and in a very similar shape and pattern.

So that leads to a correlation, a link between the amount of carbon dioxide in the atmosphere and the average global temperature.

Now, a correlation isn't enough to say that there is definitely a link between the amount of carbon dioxide in the atmosphere and an increasing global temperature, but we can say that they are both very similar in pattern.

And then we can look for other data which will help to either confirm that the link is actually real or refute that claim and provide alternative explanations for those two patterns being the same.

So in other words, we need to collect more evidence to be able to state a link, an actual link between these two sets of data despite the correlation in those data.

So what does the positive correlation between global average temperature and the amount of atmospheric carbon dioxide show? A, increasing the amount of atmospheric carbon dioxide does not cause global warming.

B, increasing the amount of atmospheric carbon dioxide may cause global warming.

Or C, increasing the amount of atmospheric carbon dioxide does cause global warming.

What do you think? I'll give you five seconds to decide.

Okay, so you should have said that B, it may cause global warming is correct.

Well done if you spotted that.

So we have this correlation between atmospheric carbon dioxide and average global temperatures and how as atmospheric carbon dioxide levels are increasing, the global temperature is increasing as well.

But we need further evidence to explain how these two factors may be related.

And in fact, there's an overwhelming quantity of evidence that shows that an increasing quantity of atmospheric carbon dioxide is a major cause of global warming and the increase in average global temperatures.

So scientists can explain how increases in carbon dioxide cause global warming, why there is a direct link between these two factors.

Scientists can also predict the average global temperature that would be achieved at different levels of carbon dioxide, and they're also able to confirm their predictions with measurements.

So we can be sure of the link between an increase in carbon dioxide levels in the atmosphere and the average global temperature because of this body of evidence and detailed explanation that sits behind it.

So carbon dioxide emissions have increased significantly since the industrial revolution began in 1850.

And you can see that on the map there.

The start of the industrial revolution from then onwards sees an exponential increase in carbon dioxide emissions, whereas before the industrial revolution, those carbon dioxide emissions were pretty much steady.

And in the last 70 or so years since 1950, carbon dioxide emissions have been increasing incredibly rapidly as countries have burnt increasingly large amounts of fossil fuels driving carbon dioxide output and increasing, therefore, the emissions.

Now 99.

9% of climate scientists agree that human activity is responsible for the increase in carbon dioxide levels that have led to global warming.

Almost all of them agree with this point, and that is because the evidence is overwhelming and strong.

So what is needed for scientists to prove increased global warming is caused by human activity? A, a positive correlation between increases in average global temperature and increases in atmospheric CO2, reliable measurements for amounts of atmospheric carbon dioxide in the average global temperature, an explanation of how increased amounts of atmospheric carbon dioxide cause the average global temperature to increase, and D, results of experiments that show the explanation is correct.

What do you think? I'll give you five seconds to decide.

Okay, so you should have said that all of these things are needed for scientists to prove that an increase in global warming is caused by human activity.

Well done if you did select all of them.

Now I've said that our evidence is comprehensive and strong and scientists have additional types of evidence that strongly confirms that an increase in the levels of carbon dioxide in the atmosphere are caused by human activity.

So they have measured each type of carbon atom in the atmosphere and shown how the increase in the amount of carbon dioxide in the air has come from burning fossil fuels without doubt.

So in order to do this, they've established that carbon dioxide in the air contains a tiny amount of the radioactive version of carbon, carbon 14, the isotope carbon 14.

And they've also demonstrated how fossil fuels contain almost no carbon 14.

And with these two starting points, they've been able to show that the combustion of fossil fuels releases carbon dioxide into the atmosphere.

And by measuring carbon 14 levels in the atmosphere, they've shown how most of the additional carbon dioxide now present in the atmosphere has come from burning fossil fuels.

And that's because the quantity of radioactive carbon 14 isotopes present in the atmosphere has reduced as carbon from fossil fuels, which contains no carbon 14 has been released into the atmosphere as CO2.

Scientists have collected a wide range of other evidence as well to confirm the link between burning fossil fuels and carbon dioxide emissions from human activity and the increase in global temperatures leading to climate change.

They've also used that evidence to further develop their understanding of what global warming is and how climate change will impact it.

And these types of evidences include the measurements of average sea levels and how that is changing over time, the measurements of the frequency and the severity of extreme weather events.

So events that should be happening no more than one in 50, one in 100, one in 400 years, and how often they're actually happening, especially nowadays.

Also measurements in the change of pH of oceans.

As the oceans have dissolved more carbon dioxide, they have become more acidic and how that has changed over time.

They've also made observations about changes to ecosystems and how they have changed over time.

And with the influence of human activity.

Also, they've been able to extract ice cores which go back 800,000 years and examine the gases that were trapped within those ice cores from the atmosphere of the previous states of Earth and seeing how carbon dioxide levels have changed over the course of the last 800,000 years.

They've also been able to examine the sedimentary rock layers and use that to interpret the amount of carbon dioxide that was present in the climate that has found its way into sedimentary rock as part of the natural carbon cycle, which includes living organisms being converted into sedimentary rock when they die.

And finally, scientists have also been able to measure the size of glaciers and the Greenland ice sheet and monitor how that has changed over time, and in particular how it's changed quite significantly in the last 40 to 60 years as well.

So there's this enormous body of evidence that scientists have pulled together over many years of intense work to demonstrate how human activity is leading to climate change.

So why do scientists look for additional and different evidence for global warming? Is it A, to improve their understanding of what is happening? B, to increase the certainty that their theories are correct? Or C, to identify any other factors that might also affect what is happening? I'll give you five seconds to decide.

Okay, so you should have said that all of these are reasons why scientists look for additional evidence.

Well done if you spotted that.

To summarise the first part of our lesson, what I would like you to do is to firstly describe what the graph shows, and then I would like you to suggest what evidence there is that the increasing levels of carbon dioxide in the atmosphere is from the combustion of fossil fuels and not some other natural event.

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 what the graph shows, and you should have said that it shows the amount of carbon dioxide emitted into the atmosphere and how this has increased since 1850 when the industrial revolution began.

Also that the emissions of carbon dioxide increased slowly at first and then ever more quickly, especially after about 1950 as our combustion of fossil fuels has increased.

Then I asked you to state what evidence is there that the increasing levels of carbon dioxide in the atmosphere is from the combustion of fossil fuels.

And you should have said that we can measure different types of carbon atoms present in carbon dioxide in the atmosphere and compare that to the types of atoms, the isotopes present in fossil fuels and see how fossil fuels contain almost no carbon 14, whereas there is a small amount of carbon 14 present in the atmosphere.

And that because as fossil fuels burn, they release carbon into the atmosphere in the form of carbon dioxide.

That extra carbon, which is finding its way into the atmosphere through human activity contains almost no carbon 14 isotopes.

And therefore the quantity of carbon 14 isotopes within the atmosphere has reduced as more carbon dioxide from fossil fuels has been put into the atmosphere, which does not contain carbon 14.

Well done, if you've managed to summarise that, that's quite a complex set of points there.

So good work.

Okay, let's move on to our second point of the lesson, which is about how certain we are of this climate change data.

Okay, so we know that we are collecting vast quantities of data and this data is coming from around the world daily.

So the worldwide temperature data is collected from many different sources, land weather stations, weather balloons, ships, buoys and satellites.

And you can see in the photograph there, a weather buoy out in the ocean, which is collecting data about weather in that particular location.

Now, within any sort of data, there will always be uncertainties and some of those uncertainties in the daily measurements of temperature are due to the precision of the measuring instruments.

How precise can they actually be.

The local variations within the weather conditions at that particular point 'cause of course, weather is changing all of the time.

Also, particularly for those devices which are present within large cities, large cities themselves generate quite a warming effect.

And so that has to be balanced out with the actual temperature of the surroundings and the environment.

Also, of course, for places which are at a high altitude, it's much cooler generally speaking up there.

And therefore there's a cooling effect, essentially the reverse of warm cities, and that has to be factored in as well.

And then there are other factors which affect the local conditions and vary over time that will need to be taken into account.

So all of these factors lead to uncertainties in data.

However, the temperature measurements that are collected are analysed by four major research centres around the world, and each of those research centres uses computer models to analyse the data and independently calculate the global average temperature.

So this is being done four times over, completely separately from each other using a vast body of evidence.

And because of this vast body of evidence, this huge number of measurements, it means that any anomalous results can be identified and removed, and then the average data is then calculated from that point, and that leads to the calculation of the average global temperature.

So this is the average global temperature as collected and analysed, processed by these four different organisations, NASA, the Met Office, the National Oceanic and Atmospheric Administration, and the Japanese Meteorological Agency.

And you can see how these measurements align with each other.

No one organisation is reporting average temperatures starkly different from any of the other organisations which are doing these analyses.

And therefore we can say that this data is reliable because it has been verified independently, it's been calculated and it correlates with the, or with the data from the other organisations as well.

And so because they all agree, we can say that this data is reliable, it is good quality data, and we can be certain that this data is correct.

So why may there be uncertainties in individual temperature measurements? A, they may be measured at different altitudes.

B, they may be measured close to a large city, or C, they may be measured in different units such as Fahrenheit versus Celsius.

I'll give you five seconds to consider.

Okay, so you should have said that the first two, measurements of different altitudes and close to large cities make uncertainties appear within individual temperature measurements.

Well done.

We are also collecting vast quantities of data about atmospheric carbon dioxide.

And because we've got carbon dioxide trapped in gas bubbles within ice layers going back 800,000 years or so, we can measure what the carbon dioxide levels of the atmosphere were like 800,000 years ago and all the way up to the present day.

And you can see that data plotted there in the graph.

You can see how for millennia, thousands and thousands of years, in fact, hundreds of thousands of years, atmospheric carbon dioxide levels whilst changing have never risen above the 300 parts per million point until 1950 when it has spiked and gone further and is now at more than 420 parts per million.

Now, unlike the global temperature measurements that we were looking at just a moment ago, we can say that there is some uncertainty in this data, and that's because the individual measurements are from ice cores alone and not from a broad range of data sources like global average temperatures have been collected.

However, the uncertainties in the individual measurements are too small to affect the conclusion that we can very clearly draw just by looking at this graph that in the last 200 years, the amount of atmospheric carbon dioxide has increased far greater than it could have done without human activity, and therefore human activity is driving the increase in atmospheric carbon dioxide.

So even though there is uncertainty with this data collected from ice cores, there is not enough uncertainty to say that human activity and climate change are not an issue.

It simply demonstrates how although carbon dioxide levels have fluctuated over time, over the last 800,000 years, it hasn't fluctuated to the same degree that it has recently.

Now, there are some people who will argue against global warming and they use data to substantiate their claims. However they cherry pick their data.

For instance, they might zoom in to 150,000 years or so ago and say, well, look, the level of carbon dioxide increased rapidly at that point or several other points across the previous 800,000 years.

And therefore, what's to say that the increase in carbon dioxide levels hasn't got a natural explanation? However, what they are doing is ignoring all of the other data that disagrees with their argument, and there is so much evidence that disagrees with that argument.

Now scientists look at all the data, and when we do so, we can be certain that atmospheric carbon dioxide levels are much higher now and are increasing more quickly than at any time over the last 800,000 years.

And this is because of human activity because we are burning fossil fuels and releasing carbon dioxide into the atmosphere.

So how do scientists study historical carbon dioxide levels in the atmosphere? Do they A, study air samples trapped inside ice, B, use measurements taken millions of years ago, or C, use their understanding to calculate what they should be? I'll give you five seconds to decide.

Okay, so you should have said that scientists study air samples trapped inside ice to study historical carbon dioxide levels.

Well done if you spotted that.

So what I'd like you to do now is to summarise that part of the lesson by firstly stating why there may be some uncertainties in the data that is used to calculate the average global temperature, and then stating why the media presents views on climate change that are not backed up by scientific evidence.

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

Okay, let's check your work.

So why there may be uncertainties? Well, you might have said that this is due to the precision of the measuring instruments that are used, the local variations in weather conditions, the warming effect of large cities, the cooling effect of high altitudes and other local factors that vary over time.

Did you get all of those? Add anything that you might have missed into your work.

Well done.

And then I asked you why the media might sometimes present views on climate change that are not backed up by scientific evidence.

And you might have said that the media often reports the opinions of politicians, business leaders or others who have strong ideas of what they would like to happen in the world.

And sometimes these people want to protect their own self-interests, which could mean that they want to avoid the changes needed to reduce climate change because it might impact their business, for instance.

However, it is common for everyone at times to ignore evidence that does not support their own point of view.

So well done if you've got all of those points, do add to your work if you need to and let's move on.

Well done.

Okay, let's look at this last point then about the carbon footprint.

So the carbon footprint was introduced in the 1990s, and you might have come across it.

A carbon footprint is the total amount of greenhouse gases that are released into the atmosphere each year because of the way that person's life is led.

So the different things that you do will impact the amount of carbon dioxide that is put into the atmosphere and the things that contribute the greatest amount of carbon dioxide include driving, flying, eating meat and heating or cooling down.

So heating our homes up in winter or using air conditioning for instance in the summertime.

So what can individuals do to reduce their carbon footprint? Reduce the amount of petrol they use in cars, fly less often, reduce the amount of beef they eat, or make journeys on foot or bicycle when possible.

I'll give you five seconds to decide.

Okay, so you should have said that we could do all of these things to reduce our carbon footprint.

Well done.

So we've seen how changes to our personal behaviour can help to reduce the amount of greenhouse gases that are remitted into the atmosphere each year.

And making these changes is really important because if we all do them, they will add up to being quite substantial.

However, the majority of greenhouse gases are not emitted by individuals, but instead emitted by large scale industries and commercial activities.

So about 70% of all the carbon dioxide emissions are from just 100 companies in the world.

That's quite a staggering amount, isn't it? Now that means that international efforts will be required to reduce carbon emissions.

In 2015, most countries of the world signed a legally binding international agreement called the Paris Agreement, which they promised to take actions to limit the increase in global temperatures.

And one of the things that these countries agreed to do would be to increase the amount of electricity which is being generated using renewable energy resources such as solar panels and wind turbines.

Another thing they agreed to do was to increase the use of electricity for heating and transport and essentially move homes away from using fossil fuels and move transport in particular cars away from using fossil fuels as well, petrol and diesel.

Now these changes are substantial and will require a lot of people getting on board with these changes in a very short space of time and altogether.

So these international efforts are really important, but they are huge undertakings.

However, if they happen, they are likely to have a much bigger impact on reducing greenhouse gases than each of our individual own efforts.

However, that doesn't mean to say that we shouldn't make our own efforts.

They are really important as well.

And what they often do is put pressure on those larger companies to change their behaviours as well.

So therefore, we need to do both.

We need to both change our own individual habits and also enable our governments and large commercial companies to make the changes that they need to make as well.

So which of these will have the biggest impact on reducing greenhouse gas emissions? Walking or cycling where possible, washing clothes at lower temperatures, a law banning new petrol or diesel vehicles or turning electrical devices off when not in use, which will have the biggest impact? I'll give you five seconds to decide.

Okay, so you should have said that a law banning new petrol or diesel vehicles will have the biggest impact.

Well done if you spotted that.

Okay, to summarise this last section of our lesson, what I'd like you to do is evaluate the carbon footprints of the washing machines that are described in the table A, B, and C.

And in that data there is the mass of carbon dioxide produced during the manufacture of the washing machine, the mass of carbon dioxide produced for one wash cycle and the total mass, which is produced from 2000 wash cycles.

So by evaluating the data, what I'd like you to do is to identify the washing machines which are producing the most and least carbon dioxide in certain parts of their life cycle, and then take an overall view of the whole lifecycle, including the 2000 wash cycles and draw a summary conclusion there as well.

Then I would like you to decide if you think there should be a law that makes manufacturers reduce carbon dioxide emissions of all new washing machines.

And I'd like you to explain your answer.

So give that some good consideration.

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

Okay, let's check our work.

So for the evaluation of the washing machines, you might have said that less carbon dioxide is emitted when making washing machine B compared to making A and C and washing machine C produces the most carbon dioxide when it is made.

However, if we add up the carbon dioxide emissions in lifetime of 2000 wash cycles, washing machine A emits 6,400 kilogrammes of carbon dioxide.

B emits 8,350 kilogrammes of carbon dioxide and C emits 5,500 kilogrammes of carbon dioxide.

So over its lifetime washing machine C has the smallest carbon footprint, even though it uses the most amount of carbon dioxide in order to be made in the first place.

Well done if you've evaluated that question like that.

Then I asked you to decide whether there should be a law that makes manufacturers reduce the amount of carbon dioxide that all new washing machines emit, and to explain your answer.

So you might have agreed with that and explained that that would mean that all new washing machines would emit less carbon dioxide, and so that would mean that individuals would be able to reduce their emissions.

Or you might have disagreed with that, saying that that would limit choice and therefore be poor for consumer choice.

Or you might have explained it with different rationale as well, but the important thing is to state whether you agree or not and why, with decent good quality reasons to back up your assertion.

Well done.

Both of those were quite tricky questions.

So well done for having a go.

Okay, we've come to the end of our lesson now, and what we've seen in our lesson today is that measurements clearly show how the average global temperature is increasing with the amount of atmospheric carbon dioxide.

As one goes up, so does the other.

And we can show, scientists can show that those carbon dioxide emissions are increasing rapidly and have been since the industrial revolution in 1850.

And this is therefore because of human activity.

And there is a good explanation as to why increased carbon dioxide levels in the atmosphere cause global warming.

Now, there are some uncertainties in measuring the average global temperatures, but because there are many measurements that closely agree, we can say that this data is very reliable.

We've also seen how carbon footprints measure the amount of greenhouse gases emitted by the actions of a particular person, business or country, and how these carbon footprints can be reduced by individual and group actions.

So I hope you found today's lesson interesting.

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

Bye.