Video: GCSE Chemistry Higher Tier Pack 1 • Paper 2 • Question 5

GCSE Chemistry Higher Tier Pack 1 • Paper 2 • Question 5

05:54

Video Transcript

Changes in climate can affect the mean global sea surface temperature. Give one reason why it is difficult to predict the future mean global sea surface temperature.

Firstly, what exactly is a mean global sea surface temperature? “Sea” obviously refers to the bodies of water that surround the planet. “Surface” refers to the point where the water meets the atmosphere. “Global” refers to a measurement made many times over the surface of the Earth. And a “mean temperature” is an average over multiple temperature measurements.

So why would you imagine it might be difficult to predict the future mean global sea surface temperature? Any good predictive model must have a good understanding of the impact of any external factors on the system. In this system, some of the factors include the energy output of the Sun, the presence of pollution, greenhouse gas emissions, wind, local weather variations, rainfall, cloud coverage, and likely many many other factors. And the truth of it is that any one of these factors may have many other contributing factors.

Now let’s write this answer as a full sentence. It is difficult to predict the future mean global sea surface temperature because global sea surface temperatures are affected by many variables. We also could’ve mentioned that the system is very chaotic or that models of global sea surface temperatures are incomplete.

Explain why greenhouse gases affect the mean global sea surface temperature.

Firstly, where exactly do we find greenhouse gases? In the atmosphere. And where does most of the heat arriving at Earth come from? That’s right, the Sun. The Sun is very hot, and it emits short-wavelength radiation, which passes straight through the atmosphere. It is not absorbed by greenhouse gases.

This shortwave radiation heats the Earth’s surface, which then in turn emits long-wavelength radiation. This long-wavelength radiation is absorbed by greenhouse gases and then reemitted in all directions. Some of this long-wavelength radiation falls back to the Earth, raising its average temperature, therefore raising the mean global sea surface temperature.

We can compare this to wearing a warm puffer jacket. It locks the heat in. It doesn’t generate more heat. It just stops heat from escaping.

Now how do we turn all this into full sentences? Greenhouse gases allow short-wavelength radiation to pass through the atmosphere to the Earth’s surface. However, the gases absorb the long-wavelength radiation reflected by the surface and reemit it towards the surface. Thus, more radiation is absorbed by the sea surface, causing its temperature to rise.

Figure one shows the mean global sea surface temperature between 1880 and 2015. Explain how human activities have contributed to the trend in figure one between 1950 and 2015.

The first thing we need to identify is what the trend in figure one between 1950 and 2015 actually is. We can see from the graph that, between 1950 and 2015, there was an overall increase in the mean global sea surface temperature, by quite a substantial amount. Even though there are little ups and downs, the overall trend is what we’re looking for.

There we have the first part of our answer. Humans have contributed to the increase in mean global sea surface temperatures through, think, what are the things in the last 70 years that human beings have been doing that might have increased the global sea surface temperature?

The chief factor, as given in a clue by the previous question, is the quantity of greenhouse gases in the atmosphere. In the last 70 years, greenhouse gas emissions have skyrocketed. So what are the causes of increased greenhouse gas emissions?

The three main human activities that contribute to increased greenhouse gas emissions are burning fossil fuels, deforestation, and livestock production. Burning fossil fuels releases carbon dioxide, which is a greenhouse gas. Deforestation reduces the amount of CO₂ that’s withdrawn from the atmosphere by plants. And increased livestock production means high levels of methane output. Methane is a very potent greenhouse gas.

So humans have contributed to the increase in mean global sea surface temperatures through increased net emission of greenhouse gases. There has been an increase in the production of CO₂ by the burning of fossil fuels, and increased deforestation has led to reduced CO₂ uptake by plants. For this question, two out of the three reasons is sufficient.

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