'Scary' climate message from past 过去的气候信息很“惊人”
文章来源:未知 文章作者:meng 发布时间:2009-10-11 05:08 字体: [ ]  进入论坛
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A new historical record of carbon dioxide levels suggests current political targets on climate may be "playing with fire", scientists say.

科学家称,一个新的二氧化碳含量历史记录显示现行的气候政治目标可能是“玩火”。

Data came from samples brought up by the drilling ship Joides Resolution
Data came from samples brought up by the drilling ship Joides Resolution

Researchers used ocean sediments1(沉淀物) to plot CO2 levels back 20 million years.

Levels similar to those now commonly regarded as adequate to tackle climate change were associated with sea levels 25-40m (80-130 ft) higher than today.

Scientists write in the journal Science that this extends knowledge of the link between CO2 and climate back in time.

The last 800,000 years have been mapped relatively2 well from ice cores drilled in Antarctica, where historical temperatures and atmospheric3 content have left a series of chemical clues in the layers of ice.

But looking back further has been more problematic; and the new record contains much more precise estimates of historical records than have been available before for the 20 million year timeframe.

Sustained levels

The new research was able to look back to the Miocene period, which began a little over 20 million years ago.

At the start of the period, carbon dioxide concentrations in the atmosphere stood at about 400 parts per million (ppm) before beginning to decline about 14 million years ago - a trend that eventually led to formation of the Antarctic icecap and perennial4(四季不断的,连续多年的) sea ice cover in the Arctic.

The high concentrations were probably sustained by(由于……蒙受损失) prolonged(持续很久的) volcanic5 activity in what is now the Columbia River basin of North America, where rock formations called flood basalts(玄武岩) relate a history of molten rock flowing routinely onto the planet's surface.

In the intervening millennia6(一千年), CO2 concentrations have been much lower; in the last few million years they cycled between 180ppm and 280ppm in rhythm with the sequence of ice ages and warmer interglacial periods(间冰期).

Now, humanity's emissions7 of greenhouse gases are pushing towards the 400ppm range, which will very likely be reached within a decade.

"What we have shown is that in the last period when CO2 levels were sustained at levels close to where they are today, there was no icecap on Antarctica and sea levels were 25-40m higher," said research leader Aradhna Tripati from the University of California at Los Angeles (UCLA).

"At CO2 levels that are sustained at or near modern day values, you don't need to have a major change in CO2 levels to get major changes in ice sheets," she told BBC News.

The elevated CO2 and sea levels were associated with temperatures about 3-6C (5-11F) higher than today.



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1 sediments 8b3acb612b624abdf2c2881bc6928565     
沉淀物( sediment的名词复数 ); 沉积物
参考例句:
  • When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后,体积的70-80%是水。
  • Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。
2 relatively bkqzS3     
adv.比较...地,相对地
参考例句:
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。
3 atmospheric 6eayR     
adj.大气的,空气的;大气层的;大气所引起的
参考例句:
  • Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
  • Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。
4 perennial i3bz7     
adj.终年的;长久的
参考例句:
  • I wonder at her perennial youthfulness.我对她青春常驻感到惊讶。
  • There's a perennial shortage of teachers with science qualifications.有理科教学资格的老师一直都很短缺。
5 volcanic BLgzQ     
adj.火山的;象火山的;由火山引起的
参考例句:
  • There have been several volcanic eruptions this year.今年火山爆发了好几次。
  • Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。
6 millennia 3DHxf     
n.一千年,千禧年
参考例句:
  • For two millennia, exogamy was a major transgression for Jews. 两千年来,异族通婚一直是犹太人的一大禁忌。
  • In the course of millennia, the dinosaurs died out. 在几千年的时间里,恐龙逐渐死绝了。
7 emissions 1a87f8769eb755734e056efecb5e2da9     
排放物( emission的名词复数 ); 散发物(尤指气体)
参考例句:
  • Most scientists accept that climate change is linked to carbon emissions. 大多数科学家都相信气候变化与排放的含碳气体有关。
  • Dangerous emissions radiate from plutonium. 危险的辐射物从钚放散出来。
TAG标签: climate carbon CO2 dioxide
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