一本教会你“做对”题的6级阅读书 day5 passage1
Passage 1 Getting Warmer 086
全球变暖 《经济学人》
Getting warmer
The mountain bark beetle is a familiar pest
in the forests of British Columbia.
Its population rises and falls unpredictably,
destroying clumps of pinewood as it peaks which then regenerate
as the bug recedes. But Scott Green, who studies forest ecology
at the University of Northern British Columbia,
says the current outbreak is "unprecedented in recorded history:
a natural background-noise disturbance has become a major outbreak.
We're looking at the loss of 80% of our pine forest cover.
" Other parts of North America have also been affected,
but the damage in British Columbia is particularly severe,
and particularly troubling in a province whose economy is dominated by timber.
Three main explanations for this disastrous outbreak suggest themselves.
[01:04]It could be chance. Populations do fluctuate dramatically and unexpectedly.
[01:11]It could be the result of management practices.
[01:15]British Columbia's woodland is less varied than it used to be,
[01:19]which helps a beetle that prefers pine.
[01:22]Or it could be caused by the higher temperatures
[01:25]that now prevail in northern areas,
[01:28]allowing beetles to breed more often in summer
[01:31]and survive in greater numbers through the winter.
[01:35]The Framework Convention on Climate Change (UNFCCC),
[01:41]which the United Nations adopted at the Earth Summit in Rio de Janeiro,
[01:47]is now 17 years old. Its aim was "to achieve stabilisation
[01:52]of greenhouse-gas concentrations in the atmosphere at a level
[01:57]that would prevent dangerous man-made interference with the climate system".
[02:02]The Kyoto protocol, which set about realising those aims,
[02:07]was signed in 1997 and came into force in 2005.
[02:13]Its first commitment period runs out in 2012,
[02:17]and implementing a new one is expected to take at least three years,
[02:22]which is why the 15th conference of the parties to the UNFCCC
[02:28]that starts in Copenhagen on December 7th is such a big deal.
[02:33]Without a new global agreement,
[02:36]there is not much chance of averting serious climate change.
[02:41]Since the UNFCCC was signed, much has changed,
[02:46]though more in the biosphere than the human sphere.
[02:50]According to the Intergovernmental Panel on Climate Change (IPCC),
[02:57]the body set up to establish a scientific consensus on what is happening,
[03:02]heat waves, droughts,
[03:04]floods and serious hurricanes have increased in frequency
[03:08]over the past few decades; it reckons those trends are all likely
[03:14]or very likely to have been caused by human activity
[03:17]and will probably continue. Temperatures by the end of the century
[03:22]might be up by anything from 1.1C to 6.4C.
[03:29]In most of the world the climate changes to date are barely perceptible
[03:34]or hard to be attributed to warming. In British Columbia
[03:38]and farther north the effects of climate change are clearer.
[03:42]Air temperatures in the Arctic are rising about twice as fast
[03:47]as in the rest of the world. The summer sea ice is thinning and shrinking.
[03:52]The past three years have seen the biggest losses
[03:56]since proper record-keeping started in 1979.
[04:01]Ten years ago scientists reckoned that summer sea-ice would be gone
[04:05]by the end of this century.
[04:08]Now they expect it to disappear within a decade or so.
[04:13]Since sea-ice is already in the water,
[04:17]its melting has little effect on sea levels.
[04:20]Those are determined by temperature (warmer water takes up more room)
[04:25]and the size of the Greenland and Antarctic ice caps.
[04:30]The glaciers in south-eastern Greenland have picked up speed.
[04:34]Jakobshavn Isbrae, the largest of them, which drains 6% of Greenland's ice,
[04:41]is now moving at 12 km a year-twice as fast as it was
[04:46]when the UNFCCC was signed-and its "calving front",
[04:52]where it breaks down into icebergs, has retreated by 20km in six years.
[04:59]That is part of the reason why the sea level is now rising at 3-3.5mm a year,
[05:08]twice the average annual rate in the 20th century.
[05:13]As with the mountain bark beetle, it is not entirely clear
[05:16]why this is happening. The glaciers could be retreating
[05:21]because of one of the countless natural oscillations in the climate
[05:25]that scientists do not properly understand.
[05:28]If so, the glacial retreat could well stop,
[05:32]as it did in the middle of the 20th century after a 100-year retreat.
[05:37]But the usual causes of natural variability do not seem to explain
[05:43]he current trend, so scientists incline to the view that it is man-made.
[05:49]It is therefore likely to persist unless mankind starts to behave differently
[05:54]and there is not much sign of that happening.
[05:58]Carbon-dioxide emissions are now 30% higher than they were
[06:02]when the UNFCCC was signed 17 years ago.
[06:07]Atmospheric concentration of CO2 equivalent
[06:12](carbon dioxide and other greenhouse gases)
[06:15]reached 430 parts per million in 2008,
[06:20]compared with 280 parts per million before the industrial revolution.
[06:26]At the current rate of increase
[06:28]they could more than triple by the end of the century,
[06:31]which would mean a 50% risk of a global temperature increase of 5C.
[06:38]To put that in context, the current average global temperature
[06:43]is only 5C warmer than the last ice age.
[06:48]Such a rise would probably lead to fast-melting ice sheets,
[06:54]rising sea levels, drought, disease
[06:58]and collapsing agriculture in poor countries, and mass migration.
[07:03]But nobody really knows, and nobody wants to know.
[07:08]Some scientists think that the planet
[07:10]is already on an irreversible journey to dangerous warming.
[07:15]A few climate-change sceptics think the problem will right itself.
[07:20]Either may be correct. Predictions about a mechanism
[07:24]as complex as the climate cannot be made with any certainty.
[07:29]But the broad scientific consensus is that serious climate change is a danger,
[07:34]and this newspaper believes that, as an insurance policy against a catastrophe
[07:40]that may never happen, the world needs to adjust its behaviour
[07:44]to try to avert that threat.
[07:47]The problem is not a technological one.
[07:50]The human race has almost all the tools it needs
[07:54]to continue leading much the sort of life it has been enjoying
[07:58]without causing a net increase in greenhouse-gas concentrations
[08:03]in the atmosphere. Industrial and agricultural processes can be changed.
[08:10]Electricity can be produced by wind, sunlight, biomass or nuclear reactors,
[08:16]and cars can be powered by biofuels and electricity.
[08:21]Biofuel engines for aircraft still need some work
[08:24]before they are suitable for long-haul flights, but should be available soon.
[08:30]Nor is it a question of economics. Economists argue over the sums,
[08:36]but broadly agree that greenhouse-gas emissions can be curbed
[08:40]without flattening the world economy.