Cloudy climate change: How clouds affect Earth's temperature.
云与气候变迁：云如何影响地球温度。
Earth's average surface temperature has warmed by .8 Celsius since 1750.
自从1750年开始，地球表面的平均温度已升高了0.8摄氏度。
When carbon dioxide concentrations in the atmosphere have doubled,
当大气层的二氧化碳含量翻倍，
which is expected before the end of the 21st century, researchers project global temperatures will have risen by 1.5 to 4.5 degrees Celsius.
研究者预测全球的温度将在二十一世纪结束前上升1.5到4.5度。
If the increase is near the low end, 1.5 Celsius, then we're already halfway there,
如果升温较少，也就是1.5度的话，那么现在已经升温一半了，
and we should be more able to adapt with some regions becoming drier and less productive,
我们应更能够适应其变迁：一些区域变得更干燥、生产力更低，
but others becoming warmer, wetter and more productive.
而其他地方则变得更暖、更湿，也更肥沃。
On the other hand, a rise of 4.5 degrees Celsius
另外，4.5摄氏度的升温，
would be similar in magnitude to the warming that's occurred since the last glacial maximum 22,000 years ago,
约略等于自二万二千年前最后一次冰河时期以来的所有升温总和，
when most of North America was under an ice sheet two kilometers thick.
那时大部分的北美洲都埋于两公里深冰层之下。
So that would represent a dramatic change of climate.
那将是一种剧烈的气候变迁。
So it's vitally important for scientists to predict the change in temperature
所以科学家对于温度变化的预测是极为重要的，
with as much precision as possible so that society can plan for the future.
越精准预测，人类社会才能越早未雨绸缪。
The present range of uncertainty is simply too large to be confident of how best to respond to climate change.
目前，预测的不确定性实在太大了，以至于无法以最好的方式来处理气候变迁。
But this estimate of 1.5 to 4.5 Celsius for a doubling of carbon dioxide hasn't changed in 35 years.
但是这关于1.5到4.5摄氏度之间二氧化碳成倍增加的预测，在这35年来都没有改变。
Why haven't we been able to narrow it down?
那我们为什么无法将不确定性的落差范围缩小呢？
The answer is that we don't yet understand aerosols and clouds well enough.
答案是，我们尚未能够了解气溶胶与云层。
But a new experiment at CERN is tackling the problem.
但欧洲核子研究组织的新实验正在处理这个问题。
In order to predict how the temperature will change,
为了预测气温将如何改变，
scientists need to know something called Earth's climate sensitivity, the temperature change in response to a radiative forcing.
科学家必须了解一种叫地球气候敏感性的东西，气温会随着辐射强迫而改变。
A radiative forcing is a temporary imbalance between the energy received from the Sun and the energy radiated back out to space,
辐射强迫是介于吸收太阳能和将其释放回太空之间的一种短暂的不平衡，
like the imbalance caused by an increase of greenhouse gases.
比如温室气体增生所导致的不平衡。
To correct the imbalance, Earth warms up or cools down.
为了纠正这种不平衡，地球会增加或降低温度。
We can determine Earth's climate sensitivity from the experiment that we've already performed in the industrial age since 1750
从1750年工业革命以来所作的实验中，我们可以确定地球的气候敏感性，
and then use this number to determine how much more it will warm for various projected radiative forcings in the 21st century.
然后使用这些数据来判断在二十一世纪时它由于辐射强迫所带来的增温状况。
To do this, we need to know two things:
为此，我们必须知道两件事：
First, the global temperature rise since 1750,
首先，自从1750年来，全球气温已增高许多，
and second, the radiative forcing of the present day climate relative to the pre-industrial climate.
第二，当今气候的辐射强迫现象与前工业化时代的气候相关。
For the radiative forcings, we know that human activities have increased greenhouse gases in the atmosphere, which have warmed the planet.
对于辐射强迫来说，我们知道人类的活动造成了温室气体在大气中积累已造成地球的暖化。
But our activities have at the same time increased the amount of aerosol particles in clouds, which have cooled the planet.
与此同时，我们的活动也增加了云层中气溶胶粒子的数量，它们使地球的温度冷却。
Pre-industrial greenhouse gas concentrations are well measured from bubbles trapped in ice cores obtained in Greenland and Antarctica.
人们已准确地从在格陵兰岛和南极洲的冰芯泡泡中测量了前工业化时期温室气体的累积。
So the greenhouse gas forcings are precisely known.
所以科学家已精确地掌握了温室气体强迫的状况。

But we have no way of directly measuring how cloudy it was in 1750.
但我们仍然缺乏有效的工具来直接测量云层在1750年时的状态。
And that's the main source of uncertainty in Earth's climate sensitivity.
那便是人们对于地球气候敏感性仍然感到不确定的成因。
To understand pre-industrial cloudiness,
为了了解前工业化时期的云层状况，
we must use computer models that reliably simulate the processes responsible for forming aerosols in clouds.
我们必须使用电脑模型来模拟气溶胶云的形成过程。
Now to most people, aerosols are the thing that make your hair stick, but that's only one type of aerosol.
对许多人来说，溶胶是一种可以让你的头发卷曲的东西，但那只是多种溶胶中的一种。
Atmospheric aerosols are tiny liquid or solid particles suspended in the air.
大气气溶胶是一种微小的液体，或是一种悬浮于空气中的固态颗粒。
They are either primary, from dust, sea spray salt or burning biomass,
它们要么是那些主要来自灰尘、浪花盐、生物质的燃烧，
or secondary, formed by gas to particle conversion in the atmosphere, also known as particle nucleation.
要么就是转化自大气中的粒子，也就是所谓的粒子成核。
Aerosols are everywhere in the atmosphere,
气溶胶无所不在地存在于大气之中，
and they can block out the sun in polluted urban environments, or bathe distant mountains in a blue haze.
它们会在高度污染的都市环境中遮蔽阳光，或产生一层蓝色薄雾，遮蔽远处的山峦。
More importantly, a cloud droplet cannot form without an aerosol particle seed.
更重要的是，若是没有气溶胶颗粒的种子，云滴是无法形成的。
So without aerosol particles, there'd be no clouds, and without clouds, there'd be no fresh water.
因此，若是缺少了气溶胶颗粒，就没有云，没有云，就没有新鲜的水。
The climate would be much hotter, and there would be no life. So we owe our existence to aerosol particles.
气候会变得更热，生命将无法存在，因此气溶胶颗粒的存在使我们得以存活。
However, despite their importance, how aerosol particles form in the atmosphere and their effect on clouds are poorly understood.
然而，尽管它们极具重要性，人们尚未理解气溶胶颗粒是如何在大气中形成的，以及它们如何影响云。
Even the vapors responsible for aerosol particle formation are not well established
即使导致气溶胶粒子产生的蒸汽，也尚未被科学家详实研究过，
because they're present in only minute amounts, near one molecule per million million molecules of air.
因为它们仅存于一瞬之间，近似于百万亿空气中分子之一。
This lack of understanding is the main reason for the large uncertainty in climate sensitivity,
由于缺乏对其了解，导致我们对于目前对气候敏感性仍不确定，
and the corresponding wide range of future climate projections.
这也是为什么我们对于未来的气候推测是如此不确定的原因了。
However, an experiment underway at CERN, named, perhaps unsurprisingly, 'Cloud'
然而一个在欧洲核子研究中心所进行的实验，“云”，
has managed to build a steel vessel that's large enough and has a low enough contamination, that aerosol formation can,
已成功在一个足够大的钢制容器和低污染条件下形成气溶胶，
for the first time, be measured under tightly controlled atmospheric conditions in the laboratory.
这也是第一次气溶胶可以在实验室中被科学家严密地控制、追踪与测量。
In its first five years of operation,
在最初五年的运作过程中，
Cloud has identified the vapors responsible for aerosol particle formation in the atmosphere,
“云”已确定了与大气中气溶胶形成过程所相关的蒸汽，
which include sulfuric acid, ammonia, amines, and biogenic vapors from trees.
它们包涵了硫酸、氨、胺以及来自树木的生物蒸汽。
Using an ionizing particle beam from the CERN proton synchrotron,
利用来自欧洲核子研究中心的质子同步加速器所取得的电离粒子束，
Cloud is also investigating if galactic cosmic rays enhance the formation of aerosols in clouds.
这个“云”实验也正在调查银河宇宙射线是否会增强气溶胶云的形成。
This has been suggested as a possible unaccounted natural climate forcing agent
科学家指出，这可能是一种潜在的得以改变自然气候强迫的因子，
since the flux of cosmic rays raining down on the atmosphere varies with solar activity.
因为宇宙射线穿过大气而下，会随着太阳活动而改变。
So Cloud is addressing two big questions: Firstly, how cloudy was the pre-industrial climate?
因此“云”尝试解决两大问题：首先，工业化前的气候中，云层的状态为何？
And, hence, how much have clouds changed due to human activities?
有多少的云层变化是由人类活动所引致的？
That knowledge will help sharpen climate projections in the 21st century.
这些知识将有助于增强科学家在二十一世纪的气候预测。
And secondly, could the puzzling observations of solar climate variability in the pre-industrial climate
其次，关于工业化时代以前太阳气候变化的谜题，
be explained by an influence of galactic cosmic rays on clouds?
我们可以拿云层上银河宇宙射线的影响来解释这一现象吗？
Ambitious but realistic goals when your head's in the clouds.
即便毫无头绪，这依然是一个雄心勃勃、可以实现的目标。