Directions (next ten questions) : Read the following passage carefully and answer the questions. Certain words/phrases are given in bold to help you locate them while answering some of the questions.
The Arctic is the canary in global-warming. Canaries expired in contact with gases such as carbon monoxide and methane, warning miners to leave the area. The Arctic sea is similarly sensitive to changes which might otherwise not be obvious as the Earth warms up in response to more of another gas, carbon dioxide. The area of the Arctic Ocean covered by ice at the height of summer has been shrinking by 11% a decade for the past 35 years. But the details are obscure-because gathering data in the Arctic Ocean is hard. But, a systematic approach to that gathering has begun. The Marginal Ice Zone (MIZ) programme, paid for by the United States Navy, has laid dozens of devices. These measure the thickness of the icy layer, and also the salinity, temperature, oxygen concentration, organic-matter composition and movement of the seawater beneath. With luck, the MIZ's researchers with their elaborate network of sensors and instrument-laden robots known as Seagliders will gather the largest quantity of data yet collected on the seasonal melting of the Arctic ice sheet and thus find out exactly what song the Arctic canary is singing.
Monitoring sea ice is a fairly recent activity. It began seriously in the 1950s, from aboard nuclear submarines. Satellite monitoring started in 1979. Since then the summer sea ice has shrunk by 12% a decade. That is consistent with the trend predicted by climate-change models over the past three decades, an indication that their mathematical simulations of global warming are roughly right. Scientists have constructed a record of the Arctic past suggest that the summer sea ice is at its lowest level for at least 2000 years. Six of the hottest years on record- going back to 1880- have occurred since 2004. According to the Intergovernmental Panel on Climate Change (IPCC), the last time the polar regions were significantly warmer was about 1,25,000 years ago. This transformation is in fact happening faster than anyone had predicted. According to the scientists, the average thickness of the pack ice has fallen by roughtly half since the 1970s, probably for two main reasons. In the summer of 2007, coastal parts of the Arctic Occean rose to 70C- bracingly swimmable. The other was a prolonged eastward shift in the early 1990s in the Arctic's prevailing winds, known as the Arctic Oscillation. This moved a lot of ice into the Atlantic and has not been replaced.
Attention has recently also been focused on lesser-known greenhouse gases, including ozone and methane, and on soot from diesel exhaust and forest fires. These are known as "short-lived climate forcers". Though they linger in the atmosphere for a relatively short time, they can have a powerful greenhouse effect. Soot, or black carbon, stays in the atmoshere for an average of six days, whereas carbon dioxide lasts for centuries, even millennia. Yet black carbon has an unusually potent warming effect in the snowy Arctic because the dark soot, after being rained or snowed onto bright snow or ice, continues to absorb heat. The UN's Environment programme estimates that reducing black carbon and methane emission could cut Arctic warming by two-thirds over the next three decades. That would not prevent the disappearance of the summer sea ice, but it might delay it by a decade or two.
Directions (next five questions): These questions have two blanks, each blank indicating that something has been omitted. Choose the set of words for each blank that best fits the meaning of the sentence as a whole.