The Climate Changers Reading Answers: IELTS Reading Practice Test

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The Climate Changers Reading Passage

Paragraph A

The idyllic idea that prehistoric humans were able to coexist peacefully with their natural surroundings has been heavily criticised in recent years. Modern humans may have begun eradicating other species from the very beginning; our ancestors have been blamed for eradicating megafauna, including giant flightless birds in Australia, mammoths in Asia, and ground sloths in North America, as they spread across the globe. In spite of this, there were only about 12 million people in the world about 6,000 years ago, which is less than a quarter of the current population of Great Britain. That's a lot fewer people than the 6.6 billion who currently inhabit the Earth, most of whom consume fossil fuels, produce greenhouse gases, and generally mess with the planet's climate as if there is no tomorrow. That humans have been the primary cause of global warming ever since our forefathers began clearing forests to plant crops at least 7,000 years ago may seem implausible to some.

Paragraph B

But that's the opinion of William Ruddiman, a climate scientist who retired from the University of Virginia in Charlottesville. He claims that climate-warming carbon dioxide and methane were being released into the atmosphere by ancient farmers well before written history was even invented. However, early farmers actually prevented Earth from entering another ice age and kept temperatures stable for thousands of years. It's hard to believe that a few stone-age farmers could have altered global weather patterns. You are not alone if you find this hard to believe. Since Ruddiman first suggested it in 2003, his idea has generated intense debate. The majority of novel ideas, especially divisive ones, are quickly forgotten. He claims that scientists can quickly eliminate such individuals using scientific methods. Even now, five years later, nobody has abandoned his concept. Instead, he claims that recent developments only serve to bolster his position. Natural explanations for the increase in greenhouse gases over the past few thousand years are the ones that are not measuring up, he claims, so we can reject them.

Paragraph C

There can be no doubt that human activities are responsible for the skyrocketing levels of carbon dioxide and other greenhouse gases that we see in the atmosphere today, which have contributed to a 0.7° C increase in average global temperature during the 20th century. Ruddiman, however, began to doubt in the late 1990s that humankind's contribution to the global greenhouse gas had not become significant until well after the advent of industrialisation. Atmospheric C02 and methane levels have fluctuated over the past 400,000 years, as discovered by an ice core drilled at the Vostok station in Antarctica. The ancient atmosphere during the last three interglacials can be pieced together from bubbles preserved in the ice.

Paragraph D

We observe a periodic pattern of increases and decreases that coincides with the arrival and departure of ice ages and has a period of about 100,000 years. These recurring patterns can be explained by the fact that the amount of sunlight striking Earth is subject to change due to regular shifts in the Earth's orbit and axis of rotation. This is one of the brief, warm interglacial periods that occur after an ice age. Within this overall trend, methane levels tend to peak at regular intervals of about 22,000 years, coinciding with the times when the Earth's orbit causes the northern hemisphere to experience its warmest summers. Because warm northern summers cause strong tropical monsoons in southern Asia, which both promote the growth of vegetation and lead to flooding, causing vegetation to rot in oxygen-poor water, emitting methane. When summers are particularly warm in the Arctic, permafrost melts for longer periods of time, allowing plants to grow and methane emissions to occur once more.

Paragraph E

In recent years, a deviation from this previously observed pattern has been observed. Around 11,000 years ago, methane levels peaked at about 700 parts per billion (ppb) before declining. Atmospheric methane levels had been declining, but they reversed course around 5,000 years ago and have been rising ever since, despite Ruddiman's estimates that they should be no more than 450 parts per billion today. Ruddiman, in collaboration with climate modellers Stephen Serves and John Kutzbach, had demonstrated that vast areas of northern Canada and Siberia would currently be covered by ice sheets if levels of these gases had continued to fall rather than rise when they did. Another ice age would be upon the world. Why, then, have atmospheric concentrations of both methane and carbon dioxide increased over the past few hundred and thousand years? What makes this interglacial period unique in comparison to others? What if we're to blame?

Paragraph F

Some 11,000 years ago, agriculture first appeared in the eastern Mediterranean, then in China, and finally in the Americas. Clearing forests releases large amounts of stored carbon as the wood decays or is burned, and flooded rice paddies release methane in the same way that wetlands do. Ruddiman started looking into agricultural history books and articles to learn more about the origins of farming. Based on these findings, we know that rice cultivation in Asia experienced a dramatic upswing sometime around the year 5000 BCE, with the trend quickly spreading across China and Southeast Asia. At least this explained where the sudden increase in methane levels could have come from.  

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