Cloudy climate change: How clouds affect Earth's temperature - Jasper Kirkby

難以捉摸的氣候變遷：雲如何影響地球溫度 - 亞斯培．柯克比

譯者: Geoff Chen 審譯者: Zhiting Chen

Cloudy climate change: How clouds affect Earth's temperature.

難以捉摸的氣候變遷： 雲如何影響地球溫度

Earth's average surface temperature has warmed by .8 Celsius since 1750.

自從 1750 年開始，地球表面的 平均溫度已升高了攝氏 0.8 度

When carbon dioxide concentrations in the atmosphere have doubled,

當大氣層的二氧化碳逐漸累積

which is expected before the end of the 21st century,

研究者預測

全球的溫度 將在廿一世紀結束前

researchers project global temperatures

will have risen by 1.5 to 4.5 degrees Celsius.

將上升 1.5 到 4.5 度

If the increase is near the low end, 1.5 Celsius,

如果升溫較為接近低點 也就是 1.5 度的話

then we're already halfway there, and we should be more able to adapt

那麼我們便來到半途了 我們應更能夠適應其變遷：

with some regions becoming drier and less productive,

一些區域變得更乾燥、更缺地力

but others becoming warmer, wetter and more productive.

而其他地方則變得 更暖、更濕，也更肥沃

On the other hand, a rise of 4.5 degrees Celsius would be similar in magnitude

另外，攝氏 4.5 的升溫，約略等於

to the warming that's occurred since the last glacial maximum 22,000 years ago,

自二萬二千年前最後一次 冰河時期以來的所有升溫總和

when most of North America was under an ice sheet two kilometers thick.

那時大部份的北美洲 都埋於兩公里深冰層之下

So that would represent a dramatic change of climate.

那將是一種劇烈的氣候變遷

So it's vitally important for scientists to predict the change in temperature

這意謂著科學家對於 溫度變化的預測是極為重要的

with as much precision as possible so that society can plan for the future.

越精準預測，人類社會 才能越早未雨綢繆

The present range of uncertainty is simply too large

目前，預測的不確定性實在太大了

to be confident of how best to respond to climate change.

以至於無法以最好的方式來處理氣候變遷

But this estimate of 1.5 to 4.5 Celsius for a doubling of carbon dioxide

但是這關於攝氏 1.5 到 4.5 度之間 二氧化碳成倍增加的預測

hasn't changed in 35 years.

在這 35 年來已無改變

Why haven't we been able to narrow it down?

那我們為什麼無法將不確定性的 落差範圍縮小呢？

The answer is that we don't yet understand aerosols and clouds well enough.

答案是，我們尚未能夠了解氣溶膠與雲層

But a new experiment at CERN is tackling the problem.

但歐洲核子研究組織 (CERN) 的 新實驗正在處理這個問題

In order to predict how the temperature will change,

為了預測氣溫將如何改變

scientists need to know something called Earth's climate sensitivity,

科學家必須了解一種叫 地球氣候敏感性的東西

the temperature change in response to a radiative forcing.

氣溫會隨著輻射強迫而改變

A radiative forcing is a temporary imbalance

輻射強迫是介於吸收太陽光源 和將其釋放回太空之間的

between the energy received from the Sun and the energy radiated back out to space,

一種短暫的不平衡

like the imbalance caused by an increase of greenhouse gases.

比如溫室氣體增生所導致的不平衡

To correct the imbalance, Earth warms up or cools down.

為了導正這種不平衡 地球會增加或降低溫度

We can determine Earth's climate sensitivity

我們可以藉由我們自 1750 年工業革命以來

from the experiment that we've already

所作的實驗來決定

performed in the industrial age since 1750

地球的氣候敏感性

and then use this number to determine how much more it will warm

然後使用這些數據來判斷

for various projected radiative forcings in the 21st century.

在廿一世紀時它由於 輻射強迫所帶來的增溫狀況

To do this, we need to know two things:

為此，我們必須知道兩件事：

First, the global temperature rise since 1750,

首先，自從 1750 年來，全球氣溫已增高許多

and second, the radiative forcing of the present day climate

第二，當今氣候的輻射強迫現象

relative to the pre-industrial climate.

與前工業化時代的氣候相關

For the radiative forcings, we know that human activities

對於輻射強迫來說，我們知道人類的活動

have increased greenhouse gases in the atmosphere,

造成了溫室氣體在大氣中積累

which have warmed the planet.

已造成地球的暖化

But our activities have at the same time increased the amount

與此同時，我們的活動也增加了

of aerosol particles in clouds, which have cooled the planet.

雲層中氣溶膠粒子的數量 它們使地球的溫度冷卻

Pre-industrial greenhouse gas concentrations are well measured

人們已相當良好地 從困在格陵蘭島和

from bubbles trapped in ice cores obtained in Greenland and Antarctica.

南極洲的冰芯泡泡中 測量了前工業化時期溫室氣體的累積

So the greenhouse gas forcings are precisely known.

所以科學家已精確地 掌握了溫室氣體強迫的狀況

But we have no way of directly measuring how cloudy it was in 1750.

但我們仍然缺乏有效的工具 來直接測量雲層在 1750 年時的狀態

And that's the main source of uncertainty in Earth's climate sensitivity.

那便是人們對於地球氣候敏感性 仍然感到不確定的成因

To understand pre-industrial cloudiness,

為了了解前工業化時期的雲層狀況

we must use computer models that reliably simulate

我們必須使用電腦模型來模擬

the processes responsible for forming aerosols in clouds.

氣溶膠雲的形成過程

Now to most people, aerosols are the thing that make your hair stick,

對許多人來說，溶膠是一種 可以讓你的頭髮捲曲的東西

but that's only one type of aerosol.

但那只是多種溶膠中的一種

Atmospheric aerosols are tiny liquid or solid particles suspended in the air.

大氣氣溶膠是一種微小的液體 或是一種懸浮於空氣中的固態顆粒。

They are either primary,

它們要不是

from dust, sea spray salt or burning biomass,

主要來自灰塵、浪花鹽、生物質的燃燒

or secondary, formed by gas to particle conversion in the atmosphere,

就是轉化自大氣中的粒子

also known as particle nucleation.

也就是所謂的粒子成核

Aerosols are everywhere in the atmosphere,

氣溶膠無所不在地存在於大氣之中

and they can block out the sun in polluted urban environments,

它們會在高度污染的都市環境中遮蔽陽光

or bathe distant mountains in a blue haze.

或產生一層藍色薄霧遮蔽遠處的山巒

More importantly, a cloud droplet cannot form without an aerosol particle seed.

更重要的是，若是沒有氣溶膠顆粒的種子 雲滴是無法形成的

So without aerosol particles, there'd be no clouds,

因此，若是缺少了氣溶膠顆粒，就沒有雲

and without clouds, there'd be no fresh water.

沒有雲，就沒有新鮮的水

The climate would be much hotter, and there would be no life.

氣候會變得更熱，生命將無法存在

So we owe our existence to aerosol particles.

因此氣溶膠顆粒的存在 使我們得以存活

However, despite their importance,

然而，儘管它們極具重要性

how aerosol particles form in the atmosphere

人們尚未理解氣溶膠顆粒 是如何在大氣中形成的

and their effect on clouds are poorly understood.

以及它們對雲的效應是如何

Even the vapors responsible for aerosol particle formation

即使那形塑氣溶膠粒子的蒸汽

are not well established

也尚未被科學家詳實研究過

because they're present in only minute amounts,

因為它們僅存於一瞬之間

near one molecule per million million molecules of air.

近似於百萬億空氣中分子之一

This lack of understanding is the main reason

對於它的無知

for the large uncertainty in climate sensitivity,

是我們對於目前對氣候敏感性 感到大量不確定性的主要原因

and the corresponding wide range of future climate projections.

這也是為什麼我們對於未來的氣候推測 是如此不確定的原因了

However, an experiment underway at CERN, named, perhaps unsurprisingly, "Cloud"

然而一個在歐洲核子研究中心 所進行的實驗﹣「雲」﹣

has managed to build a steel vessel that's large enough

已成功建立了一個足夠大的 鋼製容器和足夠低的污染排放

and has a low enough contamination, that aerosol formation can,

使得氣溶膠的形成

for the first time, be measured under tightly controlled atmospheric conditions

第一次地可以在實驗室中

被科學家嚴密地控制、追蹤與測量

in the laboratory.

In its first five years of operation, Cloud has identified the vapors

在早期五年的運作過程中 「雲」已確定了

與大氣中氣溶膠形成過程所相關的蒸氣

responsible for aerosol particle formation in the atmosphere,

which include sulfuric acid, ammonia, amines,

它們包涵了硫酸、氨、胺

and biogenic vapors from trees.

以及來自樹木的生物蒸氣

Using an ionizing particle beam from the CERN proton synchrotron,

利用來自歐洲核子研究中心的 質子同步加速器所取得的電離粒子束

Cloud is also investigating if galactic cosmic rays

這個「雲」實驗也正在調查銀河宇宙射線

enhance the formation of aerosols in clouds.

是否會增強氣溶膠雲的形成

This has been suggested as a possible unaccounted natural climate forcing agent

科學家指出，這可能是一種 潛在的得以改變自然氣候強迫的因子

since the flux of cosmic rays raining down on the atmosphere

因為宇宙射線穿過大氣而下

varies with solar activity.

會隨著太陽活動而改變

So Cloud is addressing two big questions:

因此「雲」嘗試解決兩大問題：

Firstly, how cloudy was the pre-industrial climate?

首先，工業化前的氣候中，雲層的狀態為何？

And, hence, how much have clouds changed due to human activities?

有多少的雲層變化 是由人類活動所引致的？

That knowledge will help sharpen climate projections in the 21st century.

這些知識將有助於增強 科學家在廿一世紀的氣候預測

And secondly, could the puzzling observations of solar climate variability

其次，關於工業化時代以前 太陽氣候變化的謎題，我們可以拿

in the pre-industrial climate be explained by an influence

雲層上銀河宇宙射線的影響 來解釋這一現象嗎？

of galactic cosmic rays on clouds?

即便毫無頭緒，這依然是 一個雄心勃勃、可以實現的目標

Ambitious but realistic goals when your head's in the clouds.