32. combustion engine
33. 145% / 145 per cent
35. (a) barrier
36. 46 million
37. 118 million
38. vegetation zones
39. (certain) disease(s)
40. species composition
You will hear a lecture on climate change. First you have some time to look at questions 31 to 40. [20 seconds]
Listen carefully and answer questions 31 to 40.
This lecture in Environmental Studies is on the topic of human influence on climate change. First, I’ll outline some of the factors affecting climate, then go on to discuss what has already occurred, and finish up by speculating on the effects.
Previously, we’ve covered how factors such as ocean currents and prevailing winds affect climate change naturally. However, the influence of human activity on climate is what I’ll talk about today. At first, the effect on the climate was relatively small; trees were cut down to provide fuel for fires, and, as we know, trees absorb carbon dioxide and produce oxygen so the amount of carbon dioxide in the atmosphere would have increased – but not noticeably.
So, in what ways has human activity really impacted on the climate? A major contributor was the advent of the Industrial Revolution at the end of the 18th century, combined with the invention of the combustion engine. In addition, Earth’s burgeoning population has had a marked effect on climate. The first two factors saw increased amounts of carbon dioxide being released into the atmosphere from the burning of fossil fuels, such as coal and oil. The final one, human expansion, has resulted in deforestation on such a scale that the extra carbon dioxide in the air cannot be soaked up and converted into oxygen by the remaining trees.
Okay – so what has already happened? Well, global temperatures have risen by 0.6 degrees Celsius in the last 130 years. Levels of carbon dioxide, methane and nitrous oxide gases have escalated. Carbon dioxide concentrations have climbed by 30% and methane levels have increased by 145% since the beginning of the Industrial Revolution. Gas produced by fossil fuel extraction, livestock and paddy fields is primarily responsible for the growth of methane levels. Nitrous oxide, or N2O, comes from natural sources – wet tropical forests, for instance – but it is also produced by human-related activities such as agriculture, which uses synthetic nitrogen fertilisers, rubbish disposal systems and vehicle emissions.
How do gases like carbon dioxide and methane affect the climate? Well, this is what we call the Greenhouse Effect. Under normal conditions, the sun’s rays hit the earth and some are reflected back into space. However, these gases (CO2 and methane) create a barrier in the atmosphere which prevents a proportion of the sun’s rays from being reflected back into space – and, instead, the gases become trapped in the atmosphere. It’s simple really – because the sun’s rays can’t escape, the Earth heats up.
What are the possible effects? Firstly, a rise in sea levels: we already know that the Arctic ice cap has melted and shrunk considerably and great chunks of ice have been lost from Antarctica. In 1998, it was reported that 46 million people lived in areas at risk of flooding … and the number of people at risk will increase significantly if sea levels rise. It is estimated that a rise of only 50 centimetres would put that number at 92 million. Further projections would see a rise of one metre put 118 million people in danger of losing their homes and livelihoods – not to mention the loss of prime, fertile farmland. Experts predict a rise of at least 50 centimetres over the next 50 years or so.
Secondly, there would be a modification of vegetation zones with changes in the boundaries between grassland, shrub land, forest and desert. This is already causing famine in arid areas of north-eastern Africa, and has instigated – and will continue to instigate – mass movements of people away from dry regions. What we are seeing now is only the first stage, with temporary camps for climate refugees already at overcapacity; in the future, there will be significant migration resulting in extreme overcrowding of towns and cities.
Another potentially disastrous effect of climate change is an increase in the range and distribution of pests which could bring about an increase in the prevalence of certain diseases. If we think of the malaria-carrying mosquito, for example, which thrives in warmer regions – at the moment, about 45% of the world’s population is exposed to malaria – but with an increase in temperature, there will be many millions more cases of malaria a year.
The last effect I’m going to mention today is the change in ecosystems. Global warming will influence species composition – for both fauna and flora – such that some animal species will disappear and others will multiply; and it’ll be the same for plants and trees. It is predicted that around two-thirds of the world’s forests will undergo major changes of some kind. Scientists also expect deserts will become hotter and, of course, desertification will continue at an increasingly worrying rate and will become harder, if not impossible, to reverse.
What can we do to stop the process? Well, that’s the subject of next week’s lecture – so I hope to see you all there.
Narrator: That is the end of section 4. You now have half a minute to check your answers. [30 seconds]
That is the end of the listening test. You now have 10 minutes to transfer your answers to the listening answer sheet.