Passage 1 Getting Warmer 086
全球變暖 《經(jīng)濟(jì)學(xué)人》
[00:01]Getting warmer
[00:03]The mountain bark beetle is a familiar pest
[00:06]in the forests of British Columbia.
[00:09]Its population rises and falls unpredictably,
[00:13]destroying clumps of pinewood as it peaks which then regenerate
[00:17]as the bug recedes. But Scott Green, who studies forest ecology
[00:23]at the University of Northern British Columbia,
[00:26]says the current outbreak is "unprecedented in recorded history:
[00:32]a natural background-noise disturbance has become a major outbreak.
[00:37]We're looking at the loss of 80% of our pine forest cover.
[00:43]" Other parts of North America have also been affected,
[00:47]but the damage in British Columbia is particularly severe,
[00:51]and particularly troubling in a province whose economy is dominated by timber.
[00:58]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.
