VOA标准英语2012--Greenhouse Gas Speeded Ice Age Melting

Greenhouse Gas Speeded Ice Age Melting

A new study in the Journal Nature provides compelling evidence that carbon dioxide was a major driver of climate change at the end of the last Ice Age.

That correlation¹ supports the prevailing² scientific view that that CO2 is also playing a major role in today’s warming global climate. 

The study analyzed³ ice and sediment⁴ samples from dozens of locations on every continent to reconstruct variations in global temperature between 20,000 and 10,000 years ago - the end of the last Ice Age.

Harvard scientist Jeremy Shakun, the study’s lead author, says climate-change skeptics have long pointed⁵ to evidence from Antarctic ice cores that rising levels of C02 in the atmosphere lagged behind the warming climate that marked the end of the Ice Age. 

But Shakun says the new study invalidates that argument by correlating CO2 levels and temperatures all across the prehistoric⁶ planet.

“So you put these two points together, the correlation of global temperature and CO2, the fact that it lags behind the CO2, and it really leaves you thinking that CO2 was the big driver of global warming at the end of the ice age.”

Other events also helped push the planet out of the ice age. A rare wobble in the Earth’s axis⁷ resulted in more sunlight hitting the northern hemisphere. Wind shifted, ice sheets melted, dumping enormous amounts of water into the North Atlantic.

Shakun says the water flow disrupted global ocean circulation and caused a seesawing⁹ of heat between the hemispheres. 

"Antarctica happens to be on the leading end of the warm end of this seesaw⁸, so it warmed first before the CO2 started to rise," he says. “The key thing to realize with this is that this wasn’t associated with the change in global temperature. The south was warming first, but it was at the expense of cooling in the north or just shifting heat around the planet.” 

Eventually, CO2 released from the deep southern ocean accelerated the warming of the Earth’s atmosphere. Shakun says that ancient story emerges from air bubbles in ice cores, tiny shells in ocean sediment and even pollen¹⁰ at many data points across time.

“We tried to get records that really are pretty highly resolved so it would have a data point on the order of every several decades out to maybe a few centuries. We didn’t pull in any records that only had data point entry of every thousand or two thousand years. That would just be too fuzzy to really answer what we wanted to answer.”

During the end of the last ice age, as the climate warmed, CO2 levels in the atmosphere rose from about 180 parts per million to about 260.

Shakun says today the CO2 concentration has risen to 392 parts per million - and it’s still climbing.

“We’ve gone up in the last hundred years about 100 ppm (parts per million). That’s on the same order as the amount we rose at the end of the ice age, which I think puts this in perspective. Clearly it’s not a small amount. Obviously rising CO2 at the end of the ice age had a huge effect on global climate, and so we raised it as much in the last century.” 

Shakun doesn’t see this trend ending any time soon unless industrial CO2 emissions¹¹ are reduced at their source: the burning of fossil fuels in power plants, cars and buildings. He says while the research strengthens the link between C02 and the Ice ages, he believes it also reinforces the importance of addressing C02-driven climate change in our own time.

1 correlation   

n.相互关系，相关，关连

参考例句：

• The second group of measurements had a high correlation with the first.第二组测量数据与第一组高度相关。
• A high correlation exists in America between education and economic position.教育和经济地位在美国有极密切的关系。

2 prevailing   

adj.盛行的；占优势的；主要的

参考例句：

• She wears a fashionable hair style prevailing in the city.她的发型是这个城市流行的款式。
• This reflects attitudes and values prevailing in society.这反映了社会上盛行的态度和价值观。

3 analyzed   

v.分析( analyze的过去式和过去分词 )；分解；解释；对…进行心理分析

参考例句：

• The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
• The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程，因为对他来说，爱是个不可分析的迷。 来自《简明英汉词典》

4 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

5 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

6 prehistoric   

adj.（有记载的）历史以前的，史前的，古老的

参考例句：

• They have found prehistoric remains.他们发现了史前遗迹。
• It was rather like an exhibition of prehistoric electronic equipment.这儿倒像是在展览古老的电子设备。

7 axis   

n.轴，轴线，中心线；坐标轴，基准线

参考例句：

• The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
• The axis of a circle is its diameter.圆的轴线是其直径。

8 seesaw   

n.跷跷板

参考例句：

• Prices have gone up and down like a seesaw this year.今年的价格像跷跷板一样时涨时跌。
• The children are playing at seesaw.孩子们在玩跷跷板。

9 seesawing   

v.使上下（来回）摇动( seesaw的现在分词 )；玩跷跷板，上下（来回）摇动

参考例句：

• The score had been seesawing from the very start. 从一开始比分就成拉锯局面。 来自《现代英汉综合大词典》

10 pollen   

n.[植]花粉

参考例句：

• Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。
• He developed an allergy to pollen.他对花粉过敏。

11 emissions   

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。