人生の軌跡を綴っていきます


by yu-fen-sun
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Is There a Climate-Change Tipping Point?

Is There a Climate-Change Tipping Point (転換点)?

Global warming — the very term sounds gentle, like a bath that grows pleasantly hotter under the tap. Many people might assume that's how climate change works too, the globe gradually increasing in temperature until we decide to stop it by cutting our carbon emissions. It's a comforting notion, one that gives us time to gauge (計る) the steady impact of warming before taking action.

There's just one problem: that's not how climate change is likely to unfold (広がる). Instead, scientists worry about potential tipping points — triggers that, once reached, could lead to sudden and irrevocable (取り返しのつかない) changes in the climate, almost without warning. It's the same phenomenon of sudden collapse that can be seen in any number of complex systems that seem perfectly stable, until they're not — ecosystems, financial markets, even epileptic seizures (てんかん発作). The trick is to identify the warning signs that indicate a tipping point — and collapse — are about to be reached and to take action to avoid them.

A new article in the Sept. 3 issue of Nature shows there may be ways to do this, since certain warning signals appear to be similar across a variety of complex systems. Researchers from Wageningen University, the University of Wisconsin and Scripps Institution of Oceanography (海洋学) found that an assortment (仕分け、分類) of systems they studied all had critical thresholds (分かれ目、境界) that could trigger change from one state to another — changes that tend to be abrupt (唐突な), not gradual. "Such threshold events don't happen that often, but they are extraordinarily important," says study co-author Stephen Carpenter of the University of Wisconsin. "They are the portals (入口、玄関) to change."

So, how do we know that change is at hand? The Nature researchers noticed one potential signal: the sudden variance (変化) between two distinct states within one system, known by the less technical term squealing. In an ecological system like a forest, for example, squealing might look like an alternation between two stable states — barren (不毛の) versus fertile (肥沃な) — before a drought (干ばつ) takes its final toll on the woodland (森林に被害を与える) and transforms it into a desert, at which point even monsoons won't bring the field back to life. Fish populations seem to collapse suddenly as well — overfishing causes fluctuations in fish stocks until it passes a threshold, at which point there are simply too few fish left to bring back the population, even if fishing completely ceases. And even in financial markets, sudden collapses tend to be preceded (先んずる) by heightened trading volatility (変わりやすさ、不安定さ) — a good sign to pull your money out of the market. "Heart attacks, algae blooms (藻の異常発生) in lakes, epileptic attacks (てんかん発作) — every one shows this type of change," says Carpenter. "It's remarkable."

In climate terms, squealing may involve increased variability (変化) of the weather — sudden shifts from hot temperatures to colder ones and back again. General instability ensues (後に続いて起きる) and, at some point, the center ceases to hold. "Before we reached a climate tipping point we'd expect to see lots of record heat and record cold," says Carpenter. "Every example of sudden climate change we've seen in the historical record was preceded by this sort of squealing."

The hard part will be putting this new knowledge into action. It's true that we have a sense of where some of the tipping points for climate change might lie — the loss of Arctic (北極の) sea ice, or the release of methane from the melting permafrost (永久凍土) of Siberia. But that knowledge is still incomplete, even as the world comes together to try, finally, to address the threat collectively. "Managing the environment is like driving a foggy (霧のかかった) road at night by a cliff (崖、絶壁)," says Carpenter. "You know it's there, but you don't know where exactly." The warning signs give us an idea of where that cliff might be — but we'll need to pay attention.

地球温暖化についてでした。
the point of no returnを既に超えてしまっていると主張する学者も少なくない
という事実もあります。
温暖化対策とそれに付随してくる経済問題、国家間の駆け引き等々
難題山積ですね。
by yu-fen-sun | 2009-09-15 00:54 | 英語関連