VOA标准英语2011--Study: Upper-Atmosphere Particles Slow P

Study: Upper-Atmosphere Particles Slow Pace of Global Warming

A recent study finds tiny particles suspended high in Earth’s atmosphere are having a greater impact on global climate than previously¹ believed.
The airborne particles, known as aerosols³, are blocking radiation from the sun, and that’s cooling the Earth's surface. According to an international team of climate researchers, this cooling has been significant enough over the past decade to slow human-induced global warming.
Predicting future weather events has always been an uncertain affair, but for climate scientists today, one thing is certain: the earth’s atmosphere is getting hotter. Global average temperatures have risen steadily⁴ during the past century, due largely to the rising concentration of CO2 and other industrial greenhouse gas emissions⁵.
But John Daniel, climate scientist at the federal government’s National Oceanic and Atmospheric⁶ Administration in Colorado, says a closer look at the data over the past decade revealed an anomaly.
“Since about 2001, it appears that the globally-averaged temperature has stopped going up as fast as it was going up in the decades before,” Daniel said.
Mt. Pinatubo eruption⁷ plume⁸
Meaning that the Earth is still warming, but at a slower-than-expected-pace. Daniel says neither climate scientists nor computer climate models predicted the slowdown. So Daniel, along with his U.S. and French collaborators, began to study systems that are not typically considered in atmospheric models, processes that could explain the slowing of the temperature increase.
“We also noticed that if you look at satellite observations, and you can also look at ground based observations from [the Hawaiian mountaintop observatory⁹ at] Mauna Loa, you see that stratospheric aerosols have been going up over this period. A lot of people in their models, after about the year 2000, neglected the impact of stratospheric aerosols,” Daniel said.
Most of us are familiar with low-altitude aerosols: soot¹⁰ and other fine particulates¹¹ from factories and vehicles that make up city smog. But Daniel says that unlike global-warming culprits such as atmospheric carbon dioxide, high-altitude aerosols actually cool the planet.
“The reason that these aerosols exert a cooling influence is because they reflect sunlight back to space that would have made it to the ground. Our understanding that stratospheric aerosols cool is not new. We've known that for a long time,” Daniel said.
So why weren’t climate scientists accounting¹² for the stratospheric aerosols in the first place? Although they are common closer to Earth, they are less abundant in the stratosphere. Terry Deshler, Professor of Atmospheric Sciences at the University of Wyoming, explains.
"So a volcano such as [Mount] Pinatubo [in the Phillipines] threw a lot of aerosol² particles up into the stratosphere and those probably were gone in about one year. But it also threw up a lot of sulfur¹³ gas. And all the sulfur in the stratosphere gets converted into sulfuric acid droplets¹⁴. These particles are so small that gravity has a very slow [small] role so that the aerosol from the Pinatubo eruption persisted in the stratosphere for about five or six years,” Deshler said.
Deshler, who was not involved in the new aerosol study, says explosive volcanic¹⁵ events comparable to the Mt. Pinatubo eruption in 1991 are rare. Five to six years after the Pinatubo eruption, climate modelers assumed the cooling effect from stratospheric aerosols had returned to the negligible levels recorded before the eruption.
But the stratospheric aerosol levels didn’t return to zero. Daniel found that they have increased over the past decade even without a major eruption. He wondered if this was the reason for the slowdown in atmospheric warming.
“We calculated the temperature increase you get from the early 2000s to 2010, (first) when you neglect stratospheric aerosols and [again] when you include the aerosols. We found t hat when you include the stratospheric aerosols, you actually get about a 20% reduction in the amount of warming you would have had over that period,” Daniel said.
The increase in stratospheric aerosols accounted for the reduction in temperature increase over the past decade. But Daniel and Deshler point out that it’s difficult to tell where the background stratospheric aerosols are coming from. Some scientists suggest the source could be smaller, more persistent¹⁶ volcanic eruptions¹⁷. Others suggest industrial sulfur emissions.
Most climate scientists agree that the best way to combat global warming isn’t to invent countermeasures. They believe the best way is to find cleaner renewable sources of energy, so we depend less on carbon-rich fossil-fuels, and avoid at least some of the expected warming over the next few decades.

 

1 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。

2 aerosol   

n.悬浮尘粒，气溶胶，烟雾剂，喷雾器

参考例句：

• They sprayed aerosol insect repellent into the faces of police.他们将喷雾驱虫剂喷在了警察的脸上。
• Aerosol particles affect visibility,climate,and our health and quality of life.气溶胶对大气能见度、气候变化以及人类健康等有重要影响。

3 aerosols   

n.气溶胶( aerosol的名词复数 )；喷雾剂；（气体中的）浮粒；喷雾器

参考例句：

• Aerosols are present throughout the atmosphere. 气溶胶存在于整个大气层。 来自辞典例句
• Deodorants are available as aerosols or roll-ons. 除臭剂有喷雾装或滚抹装。 来自辞典例句

4 steadily   

adv.稳定地；不变地；持续地

参考例句：

• The scope of man's use of natural resources will steadily grow.人类利用自然资源的广度将日益扩大。
• Our educational reform was steadily led onto the correct path.我们的教学改革慢慢上轨道了。

5 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。

6 atmospheric   

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。

7 eruption   

n.火山爆发；（战争等）爆发；（疾病等）发作

参考例句：

• The temple was destroyed in the violent eruption of 1470 BC.庙宇在公元前1470年猛烈的火山爆发中摧毁了。
• The eruption of a volcano is spontaneous.火山的爆发是自发的。

8 plume   

n.羽毛；v.整理羽毛，骚首弄姿，用羽毛装饰

参考例句：

• Her hat was adorned with a plume.她帽子上饰着羽毛。
• He does not plume himself on these achievements.他并不因这些成就而自夸。

9 observatory   

n.天文台，气象台，瞭望台，观测台

参考例句：

• Guy's house was close to the observatory.盖伊的房子离天文台很近。
• Officials from Greenwich Observatory have the clock checked twice a day.格林威治天文台的职员们每天对大钟检查两次。

10 soot   

n.煤烟，烟尘；vt.熏以煤烟

参考例句：

• Soot is the product of the imperfect combustion of fuel.煤烟是燃料不完全燃烧的产物。
• The chimney was choked with soot.烟囱被煤灰堵塞了。

11 particulates   

n.微粒，粒子( particulate的名词复数 )

参考例句：

• Techniques for controlling particulates include filtering, washing, centrifugal separation, and electrostatic precipitation. 控制颗粒污染物的技术包括过滤、洗涤、离心分离、静电沉降。 来自英汉非文学 - 环境法 - 环境法
• Only micronic particulates penetrate to the depth of the lung. 只有微细粒子穿透到肺深部。 来自辞典例句

12 accounting   

n.会计，会计学，借贷对照表

参考例句：

• A job fell vacant in the accounting department.财会部出现了一个空缺。
• There's an accounting error in this entry.这笔账目里有差错。

13 sulfur   

n.硫，硫磺（=sulphur）

参考例句：

• Sulfur emissions from steel mills become acid rain.炼钢厂排放出的硫形成了酸雨。
• Burning may produce sulfur oxides.燃烧可能会产生硫氧化物。

14 droplets   

n.小滴( droplet的名词复数 )

参考例句：

• Droplets of sweat were welling up on his forehead. 他额头上冒出了滴滴汗珠。 来自辞典例句
• In constrast, exhaled smoke contains relatively large water droplets and appears white. 相反，从人嘴里呼出的烟则包含相当大的水滴，所以呈白色。 来自辞典例句

15 volcanic   

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。

16 persistent   

adj.坚持不懈的，执意的；持续的

参考例句：

• Albert had a persistent headache that lasted for three days.艾伯特连续头痛了三天。
• She felt embarrassed by his persistent attentions.他不时地向她大献殷勤，使她很难为情。

17 eruptions   

n.喷发，爆发( eruption的名词复数 )

参考例句：

• There have been several volcanic eruptions this year. 今年火山爆发了好几次。 来自《简明英汉词典》
• Over 200 people have been killed by volcanic eruptions. 火山喷发已导致200多人丧生。 来自辞典例句