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我们可以通过改造撒哈拉大沙漠来阻止气候变化吗?

Can We Terraform the Sahara to Stop Climate Change?

《真实工程》视频由Brilliant为您呈献
This episode of real engineering is brought to you by brilliant,
这是一个教你像个工程师一样思考并解决问题的网站
a problem solving website that teaches you to think like an engineer.
气候正在发生变化
We have been hearing it for years.
这是一个老生常谈的问题
Climate change is happening.
现在就让我来告诉你气候的真相
What I am about to present to you is fact.
已由若干同业评估论文确认其可靠性
These are reliable measurements with multiple peer reviewed papers confirming the information.
大气二氧化碳已达到
Atmospheric carbon dioxide levels are the
40万年来的最高水平
highest they have been in over 400 thousand years,
这是在我们分析了百年来
confirmed by our analysis of hundreds
北极冰核 树核
of samples of arctic ice core, tree cores
以及化石中的同位素比率后所得出的结论
and isotope ratios in fossils.
自工业革命以来
Average global temperatures have risenby 0.8 degrees celsius
全球平均气温上升了0.8℃
since the industrial revolution began,
其中2/3的气温上升发生在1975年至今
with two third of that changeoccurring since 1975.
铁证如山
The evidence is overwhelming.
这就是事实
This is fact.
不容辩驳
You are wrong if you deny it.
如果气温持续上升
If these trends continue,
不用说如果 因为气温就是会继续上升
and I really shouldn’t say if because they will continue, we are
未来会出现更强烈的风暴
going to continue seeing stronger storms,
更灼人的热浪和更严重的干旱
more heat waves and droughts, sea levels will
在未来三十年里 海平面会持续上升
continue to rise even after the ice caps have vanished
即使是在夏季之后的数月 那时冰盖已经完全消融
in the summer months in about 30 years,
值得关注的是
and to really make you motivated to care
世界经济也会因此受挫
about this, the world’s economy will suffer.
在减少碳排放的技术方面
We have been making strides
我们已经取得了长足进步 但在真正利用这些技术
in the technology required to reduce our emissions of carbon dioxide,
减少碳排放方面 我们还需要加快步伐
but the change over is happeningtoo slowly.
过去十年间 人类世界在减少碳排放中
The most effective thing our world has done
取得的最大成效就是
in the past 10 years in battling carbon emissions
顺利渡过全球经济危机
was going through a global financial crisis.
和我的祖国一样 各国一直未能达成碳排放目标
Countries, like my own, are continually missingcarbon targets.
2020年之后
We are going face up to 600 million euro
除非我们实现了减少20%碳排放量的承诺
in fines every year after 2020 until we fulfil
否则将面临每年多达6亿欧元的罚款
our promise of reducing our carbon emissionsby 20%.
这笔钱将以碳税的形式由我们承担
That money is going to come out of our pockets through carbon taxes.
也许只有这样 我们才会真正重视气候变化
Maybe then we will start to take climate changeseriously.
二氧化碳排放量没有显著降低
We aren’t making significant decreases in carbon dioxide emissions.
只是保持稳定了 但这还不够
We’ve only really leveled out which is not good enough.
如果我们能在减少碳排放方面有所作为
So if we are making a difference
也许我们就能逆转气候变化
by reducing emissions maybe we can reverse climate change.
也许我们可以重建我们的气候系统
Maybe we can engineer our climate,
为此人们提出了很多方案
and there has been multiple suggested methods of doing that.
在本视频系列中
In this new video series
我们会解释其中一些地质工程方案的原理
we’re going to explain how several geoengineering methods intend to work
以及这些实施方案可能对气候产生的影响
and the potential impact on theworld’s climate.
第一个方案是 造林计划
The first plan we will examine is Afforestation.
造林计划 不言而喻
Afforestation is pretty much self explanatory.
就是种树 让树木生长并储存二氧化碳
Plant forests, allow them to grow and store carbon in their wood.
问题是 我们很难找到这么大空间来种植
The problem we run into is finding large enough spaces to plant forests,
能明显减缓气候变暖规模的树林
that would have a significant impact on the climate
同时不会影响
and that would not negatively affect the economies
造林国家的经济
of countries employing the method.
征用耕地
Taking land that could be used
这一方法并不现实
for agriculture just isn’t a realistic solution,
没人愿意这么做
no one is going to agree to it.
我们的选择不多
Our options are limited,
但我们刚好拥有大片
but we happen to have huge expanses of land on earth that are
不能用于任何生产性活动的 沙漠
not being used for anything productive, deserts.
我知道你们的顾虑
Now I know what you are thinking,
沙漠并不适宜种植
deserts are not the best place for growing anything,
但随着水脱盐技术快速发展
but with water desalination technology rapidly advancing this isn’t
沙漠造林是有可能实现的
as far fetched as it may seem.
让我们来讨论一下
We are going to examine the
在撒哈拉和澳洲内陆沙漠
feasibility and effect of afforestation in the two largest
世界上最大的两个亚热带沙漠
subtropical deserts in the world,
之上造林的可行性和效果
the Saharaand the Australian outback.
这两个沙漠是造林的最佳选择
These are the perfect candidates for afforestation,
既没有庞大的人口占用着土地
neither have large competing human populations,
也没有农耕活动 或大量的动植物
agricultural activity, or large natural animaland plant populations.
且它们处于亚热带区域
Conveniently, they are also
植物可以全年生长 不会枯萎
in the sub-tropical zones where a 12 month growth cycle is possible,
可在最大程度上消耗二氧化碳
maximising our carbon capture potential.
为最大化二氧化碳吸收效果
To maximise our potential further,
我们需要选择合适的树种
we need to pick a suitable tree.
选择的树种要能适应当地的气候
The tree we chose will need to be suited to this climate,
能够常绿 快速生长
be ever-green, grow rapidly,
并能作为商业资源被利用
and be useful as a commercial resource.
澳大利亚巨杉是个不错的选择
The Australian Eucalyptus grandis will be candidate for this study.
还能带来额外的好处 为考拉提供栖息地
Which also comes with the added benefit of being a habitat for these cute little shits.
在考虑如何操作之前
Before even bothering to worry about how this would be done,
我们先分析一下这是否值得
let’s first see if it’s worth being done.
首先看一下撒哈拉沙漠 作为例子
Let’s first look at the Sahara as an example.
我们最终都是为了让树木吸收大气中的二氧化碳
Ultimately we are trying to sequester atmospheric carbon dioxide by storing it in wood.
每一万平方米土地可植约一千棵树
Every 10,000 square metres could hold about 1 thousand trees,
而这片位于
and taking this patch of
西经16º至东经45º之间的撒哈拉沙漠
the Sahara between the 16 degree and 50
其面积约9.8万亿平方米
degree longitudes we have about 9800 billion square
忽略基础设施用地
metres of land, ignoring land needed for infrastructure,
这片土地可种植9.8千亿棵树
that’s about 980 billion trees.
种植这么大的一片森林
Planting a forest of this size would increase the world population
全球树木就增加了33%左右
of trees by about 33 %.
这是相当可观的
That’s a lot of trees.
据估算 这样一片森林在大约一个世纪内
Estimates show that this would capture between
每年能吸收60-120亿吨碳
6 and 12 gigatonnes of carbon per year for about a century,
在这片森林进入生长缓慢的稳定状态前
before it would meet a steady state where growth would slow
二氧化碳的吸收量会和它的排放量相抵消
and carbon dioxide in would equal carbon dioxide out.
60-120亿吨树木每年能吸收
6 to 12 gigatonnes would capture
人类二氧化碳排放量的16.3%-32.6%
between 16.3 % to 32.6 % of our emissions per year,
而人类2017年排放的二氧化碳总量为368亿吨
with humans generating a total of 36.8 gigatonnes of carbondioxide in 2017.
希望人类不会栽完树之后就放任不管了
Ideally we wouldn’t just let the trees grow and forget about them,
我们需要系统性伐木
we would systematically cut them down
并用于建造
and use them for construction,
合成原料或者转化为液体生物燃料
synthetic feed-stock or convert them to liquid
以代替不断被消耗的化石燃料
biomass fuel to replace our dwindling fossil fuel supplies
并且利用发电厂的碳捕获技术
and burn that fuel in a power
燃烧这种燃料用以发电
plant with its own carbon capture technology,
此举将会进一步减少二氧化碳的排放
which would reduce emissions further,
也会为沙漠地区创造新的经济价值
and produce new economies for these desert regions.
澳大利亚的沙漠总面积是
Australia’s desert is about 60 % the size
撒哈拉沙漠的60% 因此我们能再增加
of the Sahara and so we could add an additional
60%的绿地面积
60 % to that figure,
这样我们就能达到最理想结果即每年吸收超排放量一半的碳
to bring our best case scenario to just over 50 % capture of our emissions per year.
从而使我们每年二氧化碳排放量降到70年代的水平
Bringing our emission levels per year down to levels equivalent to the 70s.
听起来好像不错
On the surface this seems great,
但它实际上将如何影响我们的环境呢?
but what effect would this actually have on our environment?
我们需要考虑多个方面
There are multiple things we need to consider,
首先是灌溉
first of all is the irrigation itself.
像这样妥善管理的森林每年大概需要
A managed forest of this nature would need
500毫米的水来灌溉
about 500 mm per year of water,
就等于说这些树每年需要
which equates to 4900 billion (4.9 x 10^12) metres cubed of water
49000亿立方米的水
per year for this number of trees.
但是我们去哪里取水呢?其成本是多少呢?
Where is all this water going to come from and at what cost?
撒哈拉沙漠的淡水供应匮乏 这不言自明
Fresh water supplies are obviously rare in the Sahara,
但出乎意料的是
but surprisingly not as rare as
它的匮乏程度不及澳洲内陆沙漠
the Australian outback.
世界上最大的地下水蓄水层
The world’s largest groundwater
位于撒哈拉沙漠底下
aquifer actually resides beneath the Sahara, and is
并由埃及 利比亚 苏丹和乍得四个国家共享
shared by four countries Egypt, Libya, Sudanand Chad.
不仅如此
And it is not alone,
新研究显示撒哈拉沙漠地下有巨大的地下水库
new studies show the Sahara is sitting on vast reservoirs of groundwater.
地下水供应对许多非洲国家来说至关重要
This groundwater supply is vital for many African countries,
因为人们的生活用水
with it often being the
主要来自这个地下水库
primary source of freshwater for their populations.
而如此工业规模的用水会引起道德问题
Draining at an industrial scale like this comes with ethical concerns,
因为这个水库中的水资源不可再生
as it is a non-renewable resource.
若按这个规模泵水
Even these vast reservoirs of water would run dry
这个巨大水库会在数年间干涸
within a few years when pumped on this scale.
而海水脱盐技术的成本
However, the cost of desalination of sea water
近年来大幅度下降
has dropped dramatically in recent years,
这要多亏诸如以色列
thanks in large part to countries like Israel,
阿联酋和沙特阿拉伯等国
The United Arab Emirates and Saudi Arabia
投资海水脱盐技术
who have invested in the technology and all get
而他们50%以上的饮用水
over 50 % of their drinking water from
都来自脱盐工厂
desalination plants.
该技术需要能源的支持 而要获得能源
This technology still requires energy and energy comes
就需要资金输入
with a cost, both monetarily
而且会增加二氧化碳的排放量
and as a source of carbon dioxide.
脱盐1立方米的水
It requires approximately 1.5 kiloWatt hours
大约需要1.5千瓦时的能量
of energy to desalinate a metre cubed of water.
而且取水时 还需要将水泵到一定的高度
We then need to pump the water to a height for distribution.
撒哈拉沙漠的平均海拔是450米
With the average elevation of the Sahara at 450 metres,
这使得每立方米水要多耗能2.5千瓦时
this would require a further 2.5 kilowatt hours per metre cubed,
所以每供应1立方米的水
bringing our total energy consumption to 4 kilowatt hours
总共需要消耗能量4千瓦时
per metre cubed of water supplied.
而碳排放量和实际成本
The cost of this
取决于消耗了多少能源
in terms of carbon footprint and actual cost will vary
但是考虑到该项目的
with the energy source used, but considering the location and nature
位置和性质
of the project, a mix of solar power
我们需要同时利用太阳能和生物质能
and biomass energy with carbon capture technology attached
而碳捕获技术则用于吸收废气
to it’s exhaust should be used.
我们先单独讨论一下太阳能的发电流程
Let’s focus on a purely solar powered process
鉴于目前利用生物质能的成本相对更高
for now, as biomass is more expensive and
且若无碳捕捉技术 其碳排放量更大
has a larger carbon footprint without carbon capture technology,
尽管随着技术的成熟 生物质能发电成本有所降低
though it would become cheaper as the project matures
这多亏了其周边的廉价燃料资源
thanks to the cheap source of fuel on its doorstep.
利用太阳能发电1每千瓦 需要花费10美分
Solar energy costs about 10 cent per kilowatt hour
而每千瓦时的太阳能电能
with a median carbon footprint of 72
含有72克的中位碳排放
grams per kWh.
将所有数据加起来得出
Putting all this together,
灌溉这片森林每年总共需要49000亿立方米的水
the total energy needed to irrigate this forest with 4900 billion
而取这么多水 需要消耗19600太瓦时的电能
metres cubed of water will be 19600 terawatt hours a year,
最终得出 给这片森林灌溉一年需要耗资19.6亿美元
at a cost of 1.96 billion dollars a year and
还会排放14亿吨的二氧化碳
a carbon footprint of 1.4 gigatonnes of carbon a year.
如果加入基础设施成本 耗资可能会达到数万亿美元
Ignoring infrastructure costs, which would likely push the initial costs into the trillions.
此时我们每年在撒哈拉沙漠吸收的碳
This puts our total carbon capture for the Sahara
最多106亿吨
at a best case scenario of 10.6 gigatonnes
而每吨二氧化碳的吸收成本为184美元
a year at a cost of 184 dollars per tonne of carbon dioxide captured.
要求贫困的非洲国家独立完成此项工程不太现实
Expecting poor African nations to fund this alone is unrealistic,
而要求各个国家缴纳碳税
so it would be reasonable
以此资助沙漠造林工程 行之有效
to expect countries to pay for this project through carbon taxes,
比如2020年 爱尔兰将启动碳税计划
like those that will be placed on Ireland in 2020,
为这项工程提供资金
and thus allowing them to offset their own carbon emissions
以抵消他们的碳排放量
with funding to the project.
燃烧一公升汽油大约排放2.6千克的二氧化碳
A litre of petrol when burned emits approximately 2.6 kilograms of carbon dioxide.
因此 按计划每公升汽油要征收
Thus placing a carbon tax of about 48 cent
48美分的碳税
per litre of petrol could pay for the project,
如果我们在该碳税计划启动后
if we sell 4 billion litres of petrol
卖掉40亿公升的汽油
with the added carbon tax, which is about the total
这相当于像爱尔兰这样的小国汽油和柴油消耗总量
petrol and diesel consumption of a small countrylike Ireland.
成本则将会较高
So it’s possible at a high cost,
如果该项目可以阻止气候变化
but if the project can stop climate change, maybe
那也值了
it’s worth it.
这是我们接下来谈到的问题
That’s the next problem we need to address.
这片森林会对世界环境产生什么实际影响呢?
What effect will the forest actually have on the world’s environment?
利用气候模型
With the help of climate models we can
我们就可以清晰的了解到
start to get a clearer picture of what all this
付出的钱和努力会所带来什么回报
money and effort would give us.
气候变暖已然成为人类最头疼的问题
Temperature being the top of our list of concerns.
当地气温最主要受到
Local temperatures would be affected most
土壤水分增加导致的
due to the evaporative cooling caused by the
蒸发 冷却效应的影响
increase in soil moisture,
由此产生的云层 大体上会增加当地降水
this would seed clouds and increase local precipitation substantially,
这样我们就能缩减目前的花费了
allowing us to reduce our ongoing costs,
因为只需要在较干旱的5-10月
with heavier irrigation only needed in drier months
进行充分的灌溉
from May to October.
局部的蒸发冷却并不会降低全球的温度
Local evaporative cooling does not decrease overall global temperatures,
只会将热量转移至大气层下
as it just transports the heat within earth’s atmosphere.
而降低大气层以下温度才是当务之急
Critically we want reduce the amount of heat retained
这就需要减少大气中的温室气体
in earth’s atmosphere by reducing
并使热量逃逸到整个生态系统之外
greenhouse gases, allowing heat to escape the system entirely.
而实践这个计划最大的问题是
One of the biggest concerns with a project
地球反射率的改变
like this is the modification of Earth’s albedo.
反射率是星体反射能力的一个衡量标准
Albedo is a measure how reflective a planet is.
高反射率表明我们的星球
A higher albedo means we reflect
更多地反射了太阳光
more sunlight back into space rather than
而非吸收太阳辐射 从而造成升温
absorbing the solar radiation, and thus increasing the temperature.
森林的反射率非常低
Forests have a very low albedo,
简直就是为吸收太阳辐射而存在的
they are literally designed to absorb solar radiation.
而雪 冰 还有沙子的反射率很高
Where as snow and ice have a very high albedo,
它们反射了大量的光射
they reflect quite a lot of light, as does sand.
在沙漠地区植树造林
Placing forests over regions where sand once resided
将减少全球的反射率
will reduce the world’s albedo,
就单这一点 森林就可以通过吸收温室气体散热
alone it will actually negate the heat lost due through reduction in greenhouse gases.
而且 在气候模型中 森林促生的云
In this climate model however the clouds seeded
帮助抵消了反射率下降带来的气温上升
from the forest helps to counteract that decrease in albedo.
研究显示
The study shows an overall decrease
虽然森林表面总体温度虽然下降了
in surface temperatures, but a significant increase in
但其周围的海洋气温显著上升
ocean temperatures surrounding the forests.
本视频中研究使用的原始论文
The conclusion of the primary paper used
其结论模棱两可
for research in this video is fairly ambiguous
对于该项目
with no definite answer to
究竟会降低地球温度还是升高
whether the project would have a net negative or net positive
这篇论文没有给出明确的答案
effect on global temperatures.
而其他资料并没有
While other papers that did not
将云层覆盖增长视为影响反射率的因素
factor the increase in cloud cover affecting albedo suggesting
这些资料显示 和那些没有造林计划的地区相比
that afforestation in the Sahara and
到2100年
Australian outback would increase global temperatures
撒哈拉沙漠和澳洲内陆的造林
by 0.12 degrees celsius by 2100,
会使全球气温升高0.12℃
compared a control model where no afforestation occured.
同样值得关注的
We also need to worry about the decrease
是造林以后 撒哈拉土壤肥沃度下降的问题
in fertilization that would occur due to Sahara
因为造林后撒哈拉的沙子将不会被刮到亚马逊和大西洋
dust no longer being transported to the Amazon and the Atlantic ocean,
这可能会抑制植物和浮游生物的生长
which would likely decrease plant and plankton growth,
进而消弥了森林提供的
and thus negate much of the carbon sequestration that
大量碳封存
this forest would provide.
脱盐工厂在排出
The desalination plants would also need
它们高浓度的盐水时 也需要谨慎行事
to carefully manage their output of highly concentrated
因为把未稀释的盐水倾泻到海里
salt water, as dumping undiluted salt water
会对当地的水生环境
into the ocean would wreak havoc on the local
造成巨大破坏
aquatic environment.
总之 我认为这是个有趣的实验
Overall, I think the idea is an interesting thought experiment,
但是实际上 我们并不能证明
but practically shows
我们付出的努力和资金会与收获成正比
little evidence of benefit for the labour and cost needed,
还可能打开潘多拉的盒子 产生不可预见的后果
and could potentially open a pandora’s box of unforeseen consequence.
因此 我们
Ultimately our best tool
对抗气候改变的最佳办法就是减少二氧化碳的排放
for combating climate change will be to decrease our carbon emissions,
而减少二氧化碳的排放的方法就是
and that solution is staring us in the face
利用成本较低的太阳能和风能
through the cheap solar and wind energy.
我们需要更多人为此行动起来
We need more people acting on this issue,
需要更多人提供资金
we need more people funding
及对可替代能源的研究
and researching alternative energy sources.
现在 你可以在Brilliant上学习太阳能课程
You can become one of those people today
来成为我们需要的人中的一个
by taking this course on solar energy on Brilliant.
通过这个课程 你将探索到
In this course you will discover
通过日光 聚光太阳能和光电管
the principal methods of harvesting energy from sunlight,
获取能量的主要方法
from both concentrated solar power and photovoltaic cells,
课程将从基础的物理原理开始
starting from the fundamental physics principles.
课程结束时
By the end of the course
你就能掌握实用的工程问题
you will be able to answer practical engineering questions
并对公用事业规模电网
and have a better understanding of the considerations
有一个更好的了解
in servicing utility scale electric grids.
最好的理解课程的方法就是 运用需要学习的概念
The best way to understand is by applying concepts yourself,
这也是Brilliant能够帮你达到的水平
which is exactly what Brilliant allows you to achieve.
这最初听起来复杂 让人望而却步
These may initially sound complicated and scary,
但Brilliant将指导你解决这些的问题
but Brilliant guides you through problems
课程被划分成若干章节 这样易于消化
that are broken into digestible sections
物理和数学的学习对我们生活非常重要
that bring you from knowing nothing to having a
Brilliant的课程将助你从对一无所知 到独树一帜
deep understanding of the physics and math that underlie everything in our lives.
振奋吗?
Feeling inspired?
那就去brilliant.org/RealEngineering免费注册吧
Then go to brilliant.org/RealEngineering andsign up for free.
前73个注册成功的人
And the first 73 people that go to
将享受8折会员年费优惠
that link will get 20 % off the annual Premium subscription.
最后 感谢大家观看 感谢所有支持Patreon的观众
As always thanks for watching and thank you to all my Patreon supporters.
如果你想了解更多
If you would like to see more from me, the links to my instagram, twitter,
点击下方链接 可以进入我的Instagram 推特 Reddit
subreddit and discord server are below.

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译制信息
视频概述

通过改造沙漠调节气候变化的利和弊。

听录译者

收集自网络

翻译译者

红玫瑰 白玫瑰🌹

审核员

审核员_Y

视频来源

https://www.youtube.com/watch?v=lfo8XHGFAIQ

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