Academic Reading Test 12.2

READING PASSAGE 2

You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2 below.

The Cause of the Next Ice Age?

If you look at a globe, you’ll see that the latitude of much of Europe and Scandinavia is the same as that of Alaska and permafrost-locked parts of northern Canada and central Siberia. Yet Europe has a climate more similar to that of the United States than northern Canada or Siberia. [Crack IELTS with Rob] It turns out that our warmth is the result of ocean currents that bring warm surface water up from the equator into northern regions that would otherwise be so cold that even in summer they’d be covered with ice. The current greatest concern is often referred to as the Great Conveyor Belt which includes what we call the Gulf Stream. This is mostly driven by the force created by differences in water temperatures and salinity. The North Atlantic Ocean is saltier and colder than the Pacific. As a result, the warm water of the Great Conveyor Belt evaporates out of the North Atlantic leaving behind saltier waters which are cooled by the cold continental winds off the northern parts of North America. Salty, cool waters settle to the bottom of the sea, most at a point a few hundred kilometres south of the southern tip of Greenland, producing a whirlpool of falling water that’s 5 to 10 miles across. This falling column of cold, salt-laden water pours itself to the bottom of the Atlantic, where it forms a great undersea river forty times larger than all the rivers on land combined, flowing south down to and around the southern tip of Africa where it finally reaches the Pacific. Amazingly, the water is so deep and so dense that it often doesn’t surface in the Pacific for as much as a thousand years after it first sank in the North Atlantic off the coast of Greenland.

The out-flowing undersea river of cold, salty water makes the level of the Atlantic fractionally lower than that of the Pacific, drawing in a strong surface current of warm, fresher water from the Pacific to replace the outflow of the undersea river. This warmer, fresher water slides up through the South Atlantic, loops around North America where it’s known as the Gulf Stream, and ends up off the coast of Europe. [Crack IELTS with Rob] By the time it arrives near Greenland, it’s cooled off and evaporated enough water to become cold and salty and sink to the ocean floor, providing a continuous feed for that deep-sea river flowing to the Pacific. These two flows - warm, fresher water in from the Pacific, which then grows salty and cools and sinks to form an existing deep-sea river - are known as the Great Conveyor Belt.

Prior to the last decades it was thought that the periods between glaciations and warmer times in North America, Europe, and North Asia were gradual. We knew from the fossil record that the Great Ice Age period began a few million years ago and during those years there were times when for hundreds or thousands of years North America, Europe, and Siberia were covered with thick sheets of ice year round. [Crack IELTS with Rob] In between these icy times, there were periods when the glaciers thawed, bare land was exposed, forests grew, and land animals (including early humans) moved into these northern regions. Most scientists figured the transition time from icy to warm was gradual, lasting dozens to hundreds of years and nobody was sure exactly what had caused it. Recently however, scientists have been shocked to discover that the transitions from ice age-like weather to contemporary-type weather usually took only two or three years. Something was flipping the weather of the planet back and forth with a rapidity that was startling.

What brought on this sudden effect was that the warm-water currents of the Great Conveyor Belt had shut down. Once the Gulf Stream was no longer flowing, it only took a year or three for the last of the residual heat held in the North Atlantic Ocean to dissipate into the air over Europe and then there was no more warmth to moderate the northern latitudes. When the summer stopped in the north, the rains stopped around the equator. [Crack IELTS with Rob] At the same time that Europe was plunged into an Ice Age, the Middle East and Africa were ravaged by drought and wind-driven firestorms. If the Great Conveyor Belt, which includes the Gulf Stream, were to stop flowing today, the result would be sudden and dramatic. Winter would set in for the eastern half of North America and all of Europe and Siberia and never go away. Within three years, those regions would become uninhabitable and nearly two billion humans would starve, freeze to death or have to relocate. Civilization as we know it probably couldn’t withstand the impact of such a crushing blow.

Most scientists involved in research on this topic agree that the culprit is global warming, which melts the icebergs on Greenland and the Arctic icepack and thus flushes cold, fresh water down into the Greenland Sea from the north diluting its salinity. When a critical threshold is reached, the climate will suddenly switch to an ice age that could last minimally 700 or so years, and maximally 100,000 years. [Crack IELTS with Rob] No one knows when it will happen but what’s almost certain is that if nothing is done about global warming, it will happen sooner rather than later.