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气候科学家如何预测未来

How Climate Scientists Predict the Future

科学秀
SciShow
过去几十亿年以来
Earth’s climate has been through a lot
地球气候发生了许多变化
over the past few billion years.
现在科学家们已经能很清楚地了解
And at this point scientists have a pretty good handle on
地球一路以来是怎么变化的
how our planet has changed over time.
但我们也要讨论未来的气候变化
But we talk about the future of the climate too,
讨论气候为什么比过去变化得快
about how it’s changing more quickly than it has
以及气温升高
in the past, and about the dangers of rising temperatures
更严重的旱灾和风暴的危害
and more severe droughts and storms.
我们预测未来气候的方法
Our methods for predicting the future of climate
与重现过去的方法有点不同
are a little different than those for reconstructing the past.
过去的事会留下物理记录以供研究
The past leaves physical records we can study in things
像树轮和冰核
like tree rings and ice cores.
未来的事需要我们更抽像一点
The future requires us to be a little more abstract.
所以 我们主要利用计算机模型来预测未来的地球气候
So, we mostly predict the future of earth’s climate using computer models,
这是通过加入尽可能多的细节到数字模型来精确模拟大气环境来实现的
mathematical reconstructions of our atmosphere that account for as much detail as possible to produce a accurate simulation.
我们已经花了几十年来建模
And it’s taken decades to build them up to the point
所以有信心说预测是准确的
where we can be confident that what they say is accurate.
事实就是如此
But it is.
模型显示气候正在变化
And what the models say is that our climate is changing,
而人类就是始作俑者
and humans are making it happen.
全球气候模型即GCMs
Global climate models, or GCMs,
产生于40 50年代
grew out of early computerized attempts
模拟地球大气的早期电算化尝试
to model the planet’s atmosphere in the 40s and 50s.
科学家们甚至没有奢求去预测未来
Scientists weren’t even trying to predict the future.
他们只是想重现
They just wanted to create a representation
地球当时的大气系统
of the earth’s atmospheric system as it was at the time.
那也够难的
That was hard enough.
过去到现在 气候模型把地球表面
Climate models, then and now, divide the earth’s surface
分成了边长几百公里的很多模块
into chunks a few hundred kilometers on a side,
每一模块都有不同的特征 比如不同的气流和地表温度
each with different properties like air movement and surface temperature.
然后计算机通过测算出模块如何相互作用
Then the computer calculates how all those chunks interact with each other
来了解事物如何随着时间变化
to see how things change over time.
那些早期模型特别简单
Those early models were super simple.
他们做一些事比如把陆地和海洋划在一起
They did things like combine land and sea
变成一块没有地势的单一潮湿表面
into a single damp surface with no geography,
或者用圆柱而不是球体来代表地球
or represent the earth as a cylinder instead of a sphere
因为极点会让计算机混淆
because the poles confused the computer.
不过幸好 这没有导致
Thankfully, this didn’t lead to
其它所有的研究都用圆柱体代表地球
a whole movement of cylinder-earthers, though.
所有简化都是必须的 因为早期超级计算机功能有限
All this simplifying was necessary because early supercomputers were kind of limited.
比如像5千字节的随机存取存储器
We’re talking, like, five kilobytes of RAM.
你的手机存储量是那个的50万倍
Your phone has, like, 500,000 times that much.
但它仍然可以处理粗糙的
Still, it was enough to come up with a crude picture
地球气流 湿地和旱地的图片
of earth’s atmospheric currents and itswet and dry regions.
最终 科学家们并非想要
Eventually, though, scientists wanted more than just
一个毫无特色的大气圆柱模型
a model of the atmosphere arounda featureless cylinder.
他们想要一个符合真实地球情况的模型
They wanted something that fit … an actual planet.
如今他们可以通过缩小模块
Now they could make the model more accurate
来使模型更加精确
by making the chunks smaller,
但那需要更多计算能力
but that would take more computing power.
再说怎么处理山体气流运动呢?
And what about the effects of mountains on air movement?
海洋暖流和寒流循环怎么办呢?
What about the warm and cold water circulating in the oceans?
为了解决这些问题 气候模型专家需要更多支持
To answer those questions, climate modelers needed more juice.
20世纪70年代 他们又开始
By the 1970s, they were also beginning to
担忧我们使用化石燃料后
worry about the greenhouse effect of the carbon dioxide
排放到大气里的二氧化碳造成的温室效应
we were adding to the atmosphere using fossil fuels.
他们认为这会锁住太阳热量
They thought it could trap the sun’s heat
引发全球变暖
and cause the planet to warm.
同时 计算机已经足够强大了
At the same time, computers were getting powerful enough
这令程序员们不只是想模拟现在的气候
that they weren’t limited to modeling the present anymore.
所以他们想开始用模型
So programmers wanted to start using models
预测未来的气候变化
to predict future changes in the climate.
但是在气象模型可以
But before a climate model can be
预测未来之前
turned loose to predict the future,
它得先能够预测过去
it has to be able to predict the past.
这就是倒推法
What’s known as hindcasting.
这是一个重要的测验
And that’s an important test,
因为如果模型的预测和
because if the model’s “predictions”match
已知的事实相吻合
what we know already happened,
我们就可以更相信
we can be more confident about
它的预测将会在未来发生
what it says will happen in the future.
气温记录在一个世纪前就有了
Temperature records go back a century or more.
如果你以1850年的数据为起点运行模型
If you start a model in 1850,
得到的结果应该能随着时间
it should be able to progress through time
和已知的气温总趋势相吻合
and match the general trends in temperature we already know happened.
在20世纪70年代末期
And by the late 1970s,
气象模型已经开始在做这个事了
climate models started to be able to do this.
在1979年 根据两个不同气象模型结果得到的一个报告
In 1979, a report pulling from two different climate models
显示地球的温度将会
suggested that the earth’s temperature would increase
随着大气二氧化碳的增加而上升
as atmospheric carbon dioxide increased.
具体而言 假设大气二氧化碳增加一倍
Specifically, assuming twice as much CO2 in the atmosphere,
他们预测温度会增加1.5到4.5摄氏度
they predicted an increase between 1.5 and 4.5 degrees Celsius,
而且这种升温趋势可能在21世纪结束之前发生
which trends suggested could happen before the 21st century was up.
这个预测范围一直被证明相当可信
That range has proven pretty reliable ever since.
而且仍然符合我们对全球变暖的预测
And it still fits the warming we expect
即变暖大约会延续到下个世纪
to happen over the next century or so,
尽管现在模型已经足够强大了(这个预测也没有变过)
even as models have become much more powerful.
所以70年代模型能回答
So models in the 70s were able to answer
一个简单的“如果…怎么办”问题:
one simple “what if” question:
如果大气中的二氧化碳量加倍会怎么办?
What happens if the amount of carbon dioxide in the atmosphere doubles?
但是现在 你的口袋里(指手机)有更多
But these days, you can carry more computing power
那些早期程序员梦寐以求的计算能力
in your pocket than those early programmers ever dreamed of,
用它把猫咪图片发给别人
and use it to send people pictures of your cat
并且阅后即焚
that disappear after 10 seconds.
老实说 这是个黄金时代
Truly, it’s a golden age.
不仅仅是猫的图片更清晰了
And not only are cat pictures better,
气象模型也更精准了
but so are climate models.
我们现在拥有的资源可以提问和解决更多细节的问题
We now have the resources to ask and answer more detailed questions.
各位 我们确实有很多问题
And boy, do we have a lot of them.
政府想要知道世上每个角落
Governments want to know what will happen, in detail,
将会发生什么
in their corner of the world.
科学家们想知道如果我们采取措施
And scientists want to know what will happen if we take measures
阻止全球气候变化
to stop global climate change,
而不是肆无忌惮地排放时会发生什么
as opposed to letting emissions run rampant.
通过已有的模型
With the models we have now,
我们可以根据未来不同的人类活动场景
we can produce more customized predictions
做出更多个性化预测
based on different scenarios of what humans might do in the future,
比如给定时间下
like how much carbon dioxide will be emitted
将会排放出多少二氧化碳
over a given amount of time
有多少土地会被用于农业
and how much land will be used for agriculture.
你也可以用模型逆向预测
You can also use these models to basically run the predictions backwards,
并且测算出
and calculate the factors
导致变暖的因素
that would lead to a certain amount of warming.
举个例子 如果政策制定者想知道
So for example, if policymakers want to see
把全球升温幅度控制在2摄氏度内
what changes should be made to limit overall global warming
需要做出什么改变的话
to 2 degrees Celsius,
他们只需要用一个有着合适参数的气象模型就好了
they just have to use a climate model with the appropriate parameters.
然而 即使这是21世纪
That said, just because it’s the 21st century
计算机已经很强大了也并不意味着
and computers are awesome now doesn’t mean
气象模型就很完美了
climate models have reached their perfect final form.
地球的大气是一个不可思议的复杂的体系
The earth’s atmosphere is an unbelievably complex system,
我们至今还没有足够强大的模型
and we don’t yet have models powerful enough
去精准地追踪所有事情
to track absolutely everything.
我们同样不能把人类做的或
We also can’t account for every single thing
将会做的每一件事算到模型里去
humans do now or might do in the future.
那么我们已经了解很多将会发生的事情
So we now know a lot about what will happen,
但为了完善预测 仍有很多工作要做的
but there’s still work left to do in perfecting our predictions.
比如 直到2012年左右
For example, up until 2012 or so,
模型也不能很好地预测海平面上升
models weren’t great at predicting sea level rise.
模型严重低估了海平面上升幅度
They undershot it pretty badly.
联合国2001和2007年的报告预测的海平面上升幅度
UN reports in 2001 and 2007 made predictions for sea level rise
低于我们通过卫星
that failed to track with
实际观察到的60%
what we observed via satellites by about 60%.
可能是因为模型没有完全考虑
That might be because the models didn’t fully account for
南极和格陵兰岛冰盖的快速变化
the rapid changes in the ice sheets over Antarctica and Greenland.
根据联合国2013年最新的报告显示
For the UN’s most recent report in 2013,
模型被重新编写 预测的海平面上升幅度上升了
the models were re-programmed and the projections for sea level rise
和我们实际看到的更加吻合
increased to be more in line with what we’re seeing happen.
我们想让模型做得更好
We want our models to do better,
一部分原因是我们想知道
in part because we want to know
气候将会怎么变
what’s going to happen to our climate,
另一部分原因是要使模型变得科学
and in part because accounting for all the variables
就得考虑所有变量
is just good science.
随着不断的改进 每一次新预测都会更加精准
With these constant improvements, every new prediction can be more detailed.
过去几十年里
And in the last couple of decades,
我们已经能开始对特定的地区进行预测
we’ve started to be able to tailor predictions for specific regions.
这很有用 因为
Which is helpful, because people and governments
不同地区的人和政府想要知道不同的事情
in different parts of the world want to know very different things.
一个南欧的农民可能想知道
A farmer in southern Europe might want to know
未来干旱是否会加重从而影响庄稼
if drought will affect their crops more severely in the future.
然而马尔代夫的岛民可能更加关心
While an islander from the Maldives might be more concerned about
国家是否会被上升的海平面完全淹没
their country being completely swallowed by rising seas.
现在我们可以试着回答那些问题
Now we can try to answer those questions,
很多答案并不乐观
and a lot of the answers aren’t encouraging.
无论你怎么看
No matter how you look at it,
模型很明显地显示全球变暖
the models are very clear that the planet is warming.
这是最早预测的事情之一
That’s one of the easiest things to predict.
我意思是 我们从1979年开始就在做这件事了
I mean, we’ve been doing it since 1979.
如果我们往大气中排放更多像二氧化碳的
If we pump more heat-trapping greenhouse gases like carbon dioxide
吸热的温室气体 地球会更加温暖
into the atmosphere, the numbers come out warmer.
除了温室气体外模型还会考虑
There are factors other than greenhouse gases that
其他因素 比如火山爆发产生的悬浮颗粒
the models take into account too, like particulate matter from volcanoes
有降温效果的燃煤电厂
and coal-burning power plants, which can have a cooling effect.
我们知道海水会吸收二氧化碳
And we know the oceans will slow warming for a while
来减缓变暖 直到饱和为止
by absorbing CO2, until they run out of capacity.
但是所有预测都认为全球变暖
But all the predictions say the warming caused by greenhouse gases
主要是温室气体导致的
will have a stronger effect.
就算出现这样的场景 即全球政府迅速行动
Even in scenarios where governments around the world work quickly
去限制和逐渐停止温室气体排放
to limit and phase out greenhouse gas emissions,
气候模型预测地球气温也会上升
climate models predict that the earth’stemperature increase
至少2度
will be at least around 2 degrees.
但在其他情形下
But in other scenarios,
比如我们采取不太激进的行动或完全不作为
where we take less aggressiveaction or no action at all,
地球的平均表面温度很可能
the planet’s average surface temperature goes up
上升至少6摄氏度
by more like 6 degrees Celsius.
如果你习惯于华氏温度的话
Which if you’re used to Fahrenheit,
对应的是11度 这太热了
that’s 11 degrees. That’s hot.
但是高温并不是气候变化的唯一结果
But higher temperatures are far from the only consequence of climate change.
通过使用模型兼其他工具
Using models, along with other tools,
研究者们预测出所有其他影响
researchers predict all kinds of other effects.
一份2014年出版的美国全球变化研究项目的综合性报告
A comprehensive report by the US Global Change Research Program,
列举了一些影响结果
published in 2014, lists some of the consequences.
它强调的是对北美的影响
It emphasizes effects on North America,
但是类似的事情在全球都会发生
but similar things would happen all over the world.
随着冰点期间隔越来越长
With more and more time passing between periods of freezing temperatures,
植物会有一个更长的生长期
plants could experience a longer growing season.
这实际上对植物吸收更多的二氧化碳
That could actually have a net positive effect of causing plants
以减少大气二氧化碳有积极影响
to take up more CO2 so less stays in the atmosphere.
但是好消息几乎就只有这个
But the good news pretty much ends there.
总的来说 世界其他地方和北美的
In general, around the world and in North America,
降水分布 包括雨和雪
there would be changes in the distribution of precipitation,
将会发生改变
including rain and snow.
这些变化会向极端化发展
The changes tend toward increasing extremes.
温暖的大气会锁住更多水汽
A warmer atmosphere holds more moisture.
所以潮湿的地区将会更潮湿
So wet regions will get wetter.
但是模型显示大规模的空气运动
But models show shifts in large-scale movements of air
也会加剧干旱
that would exacerbate dryness, too.
比如 干燥的美国西南部将会更加干燥
So for example, the dry American Southwest will get even drier.
重大灾害比如干旱 热浪
And major events like droughts, heat waves,
以及大风暴将会更加恶劣 发生得更频繁
and powerful storms will get worse and more frequent.
气候变化对大西洋飓风的影响很难被预测
The effects of climate change on Atlantic hurricanes are hard to predict.
我们不确定它是否造成了
We don’t know for sure whether it was responsible
2017年毁灭性的飓风季节
for the devastating 2017 hurricane season.
但是我们知道随着全球气温上升
But we know that as the global temperature increases,
海洋表面的温度也在上升
the temperature of the surface of the ocean does too.
温暖的海水会刺激飓风形成
And warm ocean water is hurricane fuel.
从历史来看 较暖的年份不会有更多的飓风着陆
Historically, warmer years don’t produce more hurricane landfalls.
所以我们可能只会看见(较暖年份里)风暴更强而不是更多
So we may only see stronger storms, not more of them.
但那并不一定
But that’s not a sure thing.
气候变化也将会产生其他影响
Climate change will have other kinds of effects too,
像海平面上升 冰盖融化
like rising sea levels, melting ice caps,
和洋流变化
and changes in ocean currents.
但是这需要另一整集
But it would take a whole other episode
来仔细讨论讨论
to talk about them all.
这也正是我们几年前做的事情
Which is exactly what we did a few years ago.
多亏了这几十年来气候模型的改进
Thanks to decades of work improving climate models,
我们现在才清楚地了解正在发生什么
we now have a very good idea of what’s happening,
无论是全球还是局部
both globally and regionally.
尽管我们的模型
And even though our models have gotten
这几年来越来越精细
much more detailed over the years,
但是对于气温上升的预测却从来没有改变过
those predictions of increasing temperatures have stayed constant,
这对气候模型科学是个好现象
which is a good sign for the science of climate modeling,
但也可能会引起一点担忧
but maybe also cause to be a little worried.
我们一直知道地球不只是一个潮湿的圆柱
We’ve always known the earth wasn’t just a damp cylinder.
随着我们模拟气候水平的提高
But as our ability to model the climate has improved over time,
我们已经对地球如何运作
we’ve learned a lot about how our planet works,
以及我们正在对它做什么了解很多
and what we’re doing to it.
感谢收看本集科学秀
Thanks for watching this episode of SciShow.
如果你想了解更多气候变化的影响
If you’re interested in learning more about the effects
我们有另一个视频刚好和这个话题有关
of climate change, we have another video about just that topic.
(尾声)
[OUTRO ♪]

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视频概述

观看如何用模型准确预测未来气候

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视频来源

https://www.youtube.com/watch?v=i9EyFghIt5o

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