雅思阅读备考材料：全球变暖问题

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　　A Canary in the Coal Mine

　　The Arctic seems to be getting warmer. So what?

　　A. “Climate change in the Arctic is a reality now!” So insists Robert Corell， an oceanographer with the American Meteorological Society. Wild-eyed proclamations are all too common when it comes to global warming， but in this case his assertion seems well founded.

　　B. At first sight， the ACIA’s (American Construction Inspectors Association) report’s conclusions are not so surprising. After all， scientists have long suspected that several factors lead to greater temperature swings at the poles than elsewhere on the planet. One is albedo — the posh scientific name for how much sunlight is absorbed by a planet’s surface， and how much is reflected. Most of the Polar Regions are covered in snow and ice， which are much more reflective than soil or ocean. If that snow melts， the exposure of dark earth (which absorbs heat) acts as a feedback loop that accelerates warming. A second factor that makes the poles special is that the atmosphere is thinner there than at the equator， and so less energy is required to warm it up. A third factor is that less solar energy is lost in evaporation at the frigid poles than in the steamy tropics.

　　C. And yet the language of this week’s report is still eye-catching： “the Arctic is now experiencing some of the most rapid and severe climate change on Earth.” The last authoritative assessment of the topic was done by the UN’s Intergovernmental Panel on Climate Change (IPCC) in 2001. That report made headlines by predicting a rise in sea level of between 10cm (four inches) and 90cm， and a temperature rise of between 1.4°C and 5.8°C over this century. However， its authors did not feel confident in predicting either rapid polar warming or the speedy demise of the Greenland ice sheet. Pointing to evidence gathered since the IPCC report， this week’s report suggests trouble lies ahead.

　　D. The ACIA reckons that in recent decades average temperatures have increased almost twice as fast in the Arctic as they have in the rest of the world. Skeptics argue that there are places， such as the high latitudes of the Greenland ice sheet and some buoys at sea， where temperatures seem to have fallen. On the other hand， there are also places， such as parts of Alaska， where they have risen far faster than average. Robin Bell， a geophysicist at Columbia University who was not involved in the report’s compilation， believes that such conflicting local trends point to the value of the international， interdisciplinary approach of this week’s report. As he observes， “climate change， like the weather， can be patchy and you can get fooled unless you look at the whole picture.”

　　E. And there is other evidence of warming to bolster the ACIA’s case. For example， the report documents the widespread melting of glaciers and of sea ice， a trend already making life miserable for the polar bears and seals that depend on that ice. It also notes a shortening of the snow season. The most worrying finding， however， is the evidence — still preliminary — that the Greenland ice sheet may be melting faster than previously thought.

　　F. That points to one reason the world should pay attention to this week’s report. Like a canary in a coal mine， the hypersensitive Polar Regions may well experience the full force of global warming before the rest of the planet does. However， there is a second and bigger reason to pay attention. An unexpectedly rapid warming of the Arctic could also lead directly to greater climate change elsewhere on the planet.

　　G. Arctic warming may influence the global climate in several ways. One is that huge amounts of methane， a particularly potent greenhouse gas， are stored in the permafrost of the tundra. Although a thaw would allow forests to invade the tundra， which would tend to ameliorate any global warming that is going on (since trees capture carbon dioxide， the greenhouse gas most talked about in the context of climate change)， a melting of the permafrost might also lead to a lot of trapped methane being released into the atmosphere， more than offsetting the cooling effects of the new forests.

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