Passage 1 No Hiding Place?
能量去哪里了？ 《經(jīng)濟(jì)學(xué)人》
[00:01]No hiding place?
[00:04]El Nio versus Nia
[00:07]It may seem unreasonable at the moment, as northern Europe,
[00:11]Asia and parts of America shiver in the snow,
[00:15]but 2010 may well turn out as the hottest year on record.
[00:21]Those who doubt that greenhouse gases are quite the problem
[00:25]have taken comfort from the fact that the Hadley Centre,
[00:29]part of Britain's Meteorological Office,
[00:32]reckons the warmest year since records began was 1998.
[00:37]Twelve years without a new record would, the sceptics reckon,
[00:42]be rather a large pause in what is supposed to be a rising trend.
[00:48]Computer modelling by the Met Office, though,
[00:51]gives great chances of the pause being broken.
[00:55]The fact that no record high happened in the 2000s does not mean
[01:01]that there was no warming over the decade-trends at scales coarser
[01:06]than the annual continued to point upwards,
[01:09]and other authorities suggest there have been record years during the period.
[01:15]Nor was the length of time without an annual record exceptional.
[01:20]Models simulating centuries of warming normally
[01:24]have the occasional decade in which no rise in surface temperatures
[01:29]is observed. This is because heat can be stored in other parts of the system,
[01:35]such as the oceans, for a time,
[01:38]and thus not show up on meteorologists' thermometers.
[01:43]Indeed, one reason for thinking that the coming year
[01:47]will be hotter than all known previous years is
[01:50]that the tropical Pacific is currently dumping heat. This phenomenon,
[01:56]by which heat that has been stored up in the sea over the previous few years
[02:01]is released into the atmosphere,
[02:04]is known as El Nio. A strong Nio contributed to the record temperatures in 1998.
[02:12]In 2007 and 2008 the opposite phenomenon, a cooling Nia, was happening.
[02:20]That goes some way to explaining why those years
[02:24]were chilly by the standards of the 2000s.
[02:28]And on top of El Nio, there is the sun.
[02:33]The sun's brightness fluctuates over an 11-year cycle.
[02:37]Though the fluctuation is not vast,
[02:40]it is enough to make a difference from peak to trough.
[02:45]In 2009 the sun was at the bottom of its cycle.
[02:49]Unless it is behaving particularly strangely, it should,
[02:53]over the next 12 months, begin to brighten.
[02:57]The Decadal Prediction System
[03:00]The Met Office's forecast was made using the Decadal Prediction System,
[03:06]or DePreSys. Climate models are normally used to show
[03:12]how the climate's behaviour will respond to changes in things
[03:17]like greenhouse-gas levels. But though a model's response will,
[03:22]it is hoped, be similar to the real climate's, models are caricatures,
[03:27]not portraits. Trying to force one into a state that looks exactly like
[03:33]the real climate at a specific time, as prediction requires, will distort it,
[03:39]and it is likely to misbehave as a result.
[03:42]DePreSys is an attempt to work round this "initialization" problem to
[03:48]give the model's caricature not just an all purpose resemblance
[03:53]to the way the real climate behaves, but one that captures its pose
[03:58]and expression at a particular moment.
[04:01]In 2007 the first study using DePreSys correctly predicted
[04:08]that there would be a few more years which would set no records.
[04:12]After this, it said, there would be a definite rise in temperature.
[04:18]More recently, Dr Smith and his team have been using clusters of computers
[04:23]around Britain to run multiple models with slightly different initial conditions.
[04:30]Four-fifths of these runs suggest 2010 will be warmer
[04:35]than any previous year-which could be taken as odds of four-to-one on.
[04:42]The techniques are still in their infancy.
[04:45]But they are at least making predictions that can be checked.
[04:49]Balancing the books
[04:51]Dr Smith and his colleagues are trying to predict some of
[04:56]the natural variability to come.
[04:59]Kevin Trenberth of America's National Centre for Atmospheric Research
[05:04]wants to understand in detail the natural variability.
[05:09]His quest gained unexpected prominence when one of his forcefully
[05:14]expressed e-mails on the subject found its way into the public domain
[05:19]as one of thousands of e-mails from the Climatic Research Unit of
[05:24]the University of East Anglia in the "climategate" furor of November 2009.
[05:31]Dr Trenberth was not saying that the relatively unwarmed 2000s
[05:37]were particularly exceptional. Instead, he was saying that,
[05:41]given the satellites and measurement networks
[05:44]that are being installed to monitor the climate,
[05:47]it should now be possible to identify the places and processes
[05:52]that hide energy from the eyes of climatologists.
[05:57]That would make it possible to determine
[05:59]what has actually happened to the energy trapped
[06:02]by increasing levels of greenhouse gases.
[06:06]For the first part of the decade this turns out to be possible.
[06:11]From 1998 to 2003, although surface temperatures were not rising,
[06:17]a lot of energy was taken in by the oceans.
[06:21]This is borne out by the rise in sea level during the period,
[06:25]which matches (once the additional effects of melting glaciers
[06:30]and ice sheets are taken into account) the expansion of the water
[06:34]in the oceans caused by this heating. Until the middle of the 2000s,
[06:40]therefore, the sums seem to balance.
[06:43]It is after that that the problem comes.
[06:46]Runoff's role in the rising sea level increases,
[06:51]meaning the fraction attributable to expansion,
[06:55]and thus the amount of heat taken up by the sea, has fallen.
[07:00]The missing heat must therefore be going somewhere else.
[07:04]One possibility is that it is being reflected back into space
[07:08]by changes in cloud cover. The data, however, seem to say no.
[07:14]America's CERES programme, the result of observations
[07:19]by seven different instruments on six different satellites,
[07:24]suggests the Earth has actually absorbed more energy
[07:28]and reflected away less over the past few years,
[07:32]rather than the other way round. It is all rather mysterious.
[07:37]Nevertheless, while there is a lot of scepticism in,
[07:42]around and about climate science,
[07:45]none of it is aimed at the first law of thermodynamics,
[07:49]which says that energy cannot be created or destroyed.
[07:53]The energy that the sun delivers to the Earth
[07:56]must therefore be equal to the energy
[07:58]that is reflected back into space, plus that re-emitted
[08:02]as radiation, plus that stored in some part of the atmosphere,
[08:07]the oceans or the land.
[08:10]The fact that the books cannot currently be balanced
[08:14]is therefore an admission of ignorance-an ignorance that better,
[08:19]future measurements should help abolish. That, in turn,
[08:24]should allow predictions of what the climate will do next,
[08:28]for good or ill, to become significantly better.
