在对抗气候变化的赛道上，哈佛大学的科学家们提出可以遮挡阳光，为地球降温。最近这一实验得到了微软创始人、全球第四富豪比尔盖茨的资金支持，有效加速了实验进程。据称，实验将耗费约2000万美元，而首次气球发射实验有可能在2021年6月实施。

In the race against climate change, scientists at Harvard University propose that dimming sunlight could cool down the planet. The idea has recently received support from Microsoft co-founder and 4th richest person in the world, Bill Gates, which has raised its profile significantly. The experiment will allegedly cost around $20 million. And the first balloon launch test could happen as soon as June 2021.

测试气球将把600公斤的科学设备提升到瑞典北极小镇上空。

平流层是最理想场所

The stratosphere is the ideal place

实验的原理其实很简单：在平流层（离地球表面10-50公里的大气层）挥洒微粒，这些微粒会将部分阳光反射回宇宙中去，从而为地球降温。哈佛大学的科学家们发起的这个平流层控制扰动实验（SCoPEx）将验证，将无毒的碳酸钙粉尘撒到平流层中，形成反射阳光的气溶胶，是否能抵消全球变暖的效应。 

The experiment idea is simple: spray a bunch of particles into the stratosphere — the atmospheric layer that stretches from about 10 to 50 kilometres above Earth's surface, and they will cool the planet by reflecting some of the Sun’s rays back into space. The Stratospheric Controlled Perturbation Experiment (SCoPEx), launched by Harvard University scientists, aims to examine this solution by spraying non-toxic calcium carbonate (CaCO3) dust into the stratosphere — a sun-reflecting aerosol that may offset the effects of global warming.

在现实中，科学家们已经见证过了这项原理的应用。1991年，当菲律宾皮纳图博火山爆发时，向平流层喷射了2000万英吨（约2320万吨）的二氧化硫。那次爆发产生的硫化物烟雾使全球气温下降了0.5摄氏度。大概18个月后，当地的平均气温才回到爆发前的正常水平。

@Forbes

Scientists have already witnessed the principle in action. When Mount Pinatubo erupted in the Philippines in 1991, it injected an estimated 20 million tons of sulfur dioxide into the stratosphere. The eruption created a haze of sulfate particles that cooled the planet by around 0.5°C. For about 18 months, Earth’s average temperature returned to what it was before the arrival of the steam engine.

在许多意义上来说，平流层都是提高大气层反射光能力的最理想场所。在平流层发射的小粒子可以通过大气流动扩散到整个地球，并在地球高空中存在两年或更长。如果有计划地在南北半球发射微粒，大概就能创造两块相对一致的粉尘层，将整个星球包裹保护起来，而这整个过程并不至于过于昂贵。

真正造成影响将需要数以吨计的尘埃和数百公里的羽状物，形成一个巨大的“遮阳板”。
In many ways, the stratosphere is an ideal place to try to make the atmosphere more reflective. Small particles injected there can spread around the globe and stay aloft for two years or more. If placed strategically and regularly in both hemispheres, they could create a relatively uniform blanket that would shield the entire planet. The process does not have to be wildly expensive.

并不是应对气候变化的解决方法

Is not a solution to climate change.

据悉，今年六月，SCoPEx会在瑞典基律纳附近的一座小镇做一个先导实验。瑞典航天公司已经同意帮助发射一个携带科学仪器的气球到20公里的高空。这次发射不会挥洒形成气溶胶，只是先实验一些如何操作气球，检测交流和操作系统。如果先导实验成功，才会以此为基础更进一步地试着挥洒一定量的碳酸钙粉尘。

一个大型气球将在瑞典基律纳镇上空12英里处向平流层投放2公斤白垩粉尘。

SCoPEx will take a small step in its early research this June near the town of Kiruna, Sweden, where the Swedish Space Corporation has agreed to help launch a balloon carrying scientific equipment 20 kilometers high. The launch will not release any stratospheric aerosols. Rather, it will serve as a test to maneuver the balloon and examine communications and operational systems. If successful, this could be a step towards a second experimental stage that would release a small amount of CaCO3 dust into the atmosphere.

这个项目“并不是应对气候变化的解决方法”，比尔盖茨说，“最多，这可以将这个问题延迟10至15年，到那时我们可能已经清除了排放温室气体的源头。”他还特别补充道：“当你在面对这种灾难性的问题时，证明哪些方法是死胡同，而哪些不是，是我们必须做的事。”

比尔盖茨。

The project is "not a solution to climate change," said Bill Gates, "at most, it would delay the problem for 10 or 15 years while we get rid of sources of emissions." He added, "But when you're faced with this catastrophic problem, proving which paths are dead end, which are not, we need to get going on that."

剑桥大学的大卫·金爵士表示，应该暂停推出这项技术。他说，这对天气系统来说可能是灾难性的，没有人能够预测，所以应该通过建模和其他技术收集数据。

这个项目同样面临着许多批评，反对者质疑这个为地球降温的方法只会掩盖气候变化的问题，而不能实质性地解决问题。创造本质上是人工“大气太阳伞”的方法并没有改变全球变暖危机的根源——化石燃料燃烧产生的二氧化碳量依然庞大。许多人担心此举会削弱2015年巴黎气候协定达成的全球共识，以及产生其它的负面作用。

Critics of the project are skeptical, claiming that cooling the planet in this way would only mask the problem of climate change rather than offering any sort of solutions. Engineering the climate with what is essentially an artificial sunshade doesn’t address the root cause of the crisis - the amount of carbon generated by fossil fuels all over the world. Many fear that it could undermine international commitments to act under the 2015 Paris climate agreement and could also have unwanted side-effects.

文：实习生 郭文伊 南都记者 蒋模婷

编辑：江英