IELTS Preparation Series 2, Episode 8: Air Archive

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Hello. I'm Margot Politis. Welcome to Study English, IELTS preparation.

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Today we're taking a look at tenses. We'll focus on the present perfect and simple past

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tenses, and we'll hear examples of each.

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Then, we'll practice using some adverbs of time.

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The clip we're looking at today is about greenhouse gases. Scientists have been measuring the

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concentration of certain gases, stored in ice in Antarctica. Let's find out more.

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The air archived in ice helps prove how much the level of greenhouse gases in the atmosphere

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has changed in just the last two hundred years.

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What we've found out is that indeed there were much lower concentrations pre-industrially,

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around about a third of the methane concentration that we have presently. We've seen a big increase

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in carbon dioxide, so the two main greenhouse gases in the atmosphere have increased.

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If you look back a half a million years ago, we don't see concentrations anything like

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we have presently. We can link those high concentrations of the present day uniquely

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to activities of man - combusting of fossil fuels, clearing of lands and so on, agricultural

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activities.

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As you know, there is a variety of verb tenses in English - simple, perfect and continuous.

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Tenses are used to describe 'past', 'present' and 'future' actions.

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Sometimes, we need to give more information about when an action happened, how long it

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happened for and whether it is continuing.

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When an action has been completed, we use the present perfect tense.

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Listen to Dr Etheridge use it here.