利用内拉格朗日点附近的小航天器云团为地球降温

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这篇论文探讨在日地内拉格朗日点（L1）附近部署一团小型航天器，通过散射或遮挡部分太阳光来给地球降温的地球工程方案。作者认为该方案技术上可行，约25年内可开发部署，成本约数万亿美元，占同期全球GDP不到0.5%。

HN 关注点：太阳地球工程的可行性与代价，讨论焦点集中在它只治标不治本（不解决CO2问题）、巨额投入的不可逆性以及潜在副作用。

关键词　地球工程拉格朗日点气候变化CO2

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这几条评论里：支持 1　质疑 2　补充 1

质疑遮阳降温会削弱植物光合作用，反而加剧CO2问题

这种遮挡阳光的策略并不能解决CO2问题，反而可能使其恶化。地球降低大气CO2有两大自然途径：自然风化不受影响，但植物光合作用绝对会受影响——如果从地球拿走10%的阳光，植物将CO2转化为淀粉、将水转化为氧气的能力也会相应下降。你为了对抗CO2升高的效应而限制的资源，恰恰是你对抗CO2升高所需要的资源。遮挡阳光或许能暂时降温，但会半永久性地加剧CO2问题。我们需要认识到，CO2问题并不只是一个温度问题。

mchannon查看英文原文

This strategy, to get rid of some sunlight, doesn't fix our problem with CO2. In fact, it's likely to make the problem worse. Our planet has two primary natural methods for lowering atmospheric CO2. One, natural weathering, is not impacted with this strategy. The other, plantlife, is absolutely affected. If you were to take 10% of sunlight away from Earth, then it logically follows that plants would get 10% less sunlight to convert CO2 into starches and H2O into oxygen. The resource you're trying to constrain, in the name of fighting effects of rising CO2 levels, is the very resource you need in order to fight rising CO2 levels. Sure, blocking or deflecting some light might lower Earth's temperatures temporarily, but you'd exacerbate CO2 levels semi-permanently. We, as a community, need to come to the realization that our CO2 problem is not strictly a temperature problem.

补充民主国家难以让选民接受降低舒适度的减排政策，最终大概率会走向地球工程

能源用得越多，生活越舒适；而目前能源使用与CO2排放高度相关。最大的排放国很多是民主国家——你怎么能让多数人投票选出会通过征税/管制让他们生活变得不那么舒适的政客？坦率地说，我认为人类文明会一直拖延到为时已晚，然后才试图靠地球工程来补救。《This Changes Everything》里有个情节：有人说'我们就这样改造一下'，另一人回应'那意味着我的国家会遭遇干旱'。推荐阅读《Sustainable Energy Without the Hot Air》来了解仅靠可再生能源需要减少多少能源消耗。

patrickdavey查看英文原文

I'd argue that the more energy you use, the more comfortable your life is. I'd also argue that energy use (at the moment) is pretty linked to how much CO2 you emit. A lot of the biggest emitters live in democracies. So, how do you get the majority of the population to vote in politicians who are going to make their lives less comfortable (by taxing / controlling / lessening the amount of CO2 they use)? Frankly I reckon we, as a civilization, are going to dither and procrastinate up until the point it's far far far too late to do anything meaningful, and then people will try jump on the geoengineering to hack things into place. There was a nice piece in the book "This changes everything" where they were talking about geoengineering. I'll paraphrase, but basically someone said "we'll just alter things in this way", and someone else said "that'll mean droughts in my country". Fun times ahead. If you haven't read it yet, I recommend "Sustainable Energy Without the Hot Air" [0] to get an idea of just how much less energy we need to use if we want to get by with just renewables. I really hope we can get there! [0] https://www.withouthotair.com/

质疑该方案成本前置、全有或全无，缺乏渐进投入路径，政治经济上难以推进

论文称该方案可在约25年内开发部署，成本数万亿美元，不到同期世界GDP的0.5%。'数万亿美元'是个问题——不是因为这对中和变暖来说成本特别高，而是因为它太'全有或全无'：如果只投入100亿美元，边际减排效果几乎为零，因为大部分成本都前置在最终才能产生直接效益的使能技术上。推荐阅读经典文章《The Political Economy of Very Large Space Projects》，稍作调整即可推广为《超大型项目的政治经济学》。

philipkglass查看英文原文

If it were to become apparent that dangerous changes in global climate were inevitable, despite greenhouse gas controls, active methods to cool the Earth on an emergency basis might be desirable. ... It seems feasible that it could be developed and deployed in ≈25 years at a cost of a few trillion dollars, <0.5% of world gross domestic product (GDP) over that time. The "few trillion dollars" part is a problem. Not because it represents a particularly high cost scheme for neutralizing the warming part of AGW, but because it's so all-or-nothing. If you invest "only" $10 billion in this scheme the marginal abatement effects are going to be pretty close to zero, because so much of the cost is front-loaded into enabling technologies that will eventually deliver direct benefits. I refer the interested reader to the classic The Political Economy of Very Large Space Projects: http://www.jetpress.org/volume4/space.htm With minor adjustments, it could be generalized as The Political Economy of Very Large Projects.

支持该方案相对可逆、风险较低，比其他地球工程点子更安全

我不反对地球工程这个概念。如果做这类项目，我希望能有应对措施以防弊大于利，并在投入前就把这一点纳入成本和准备。不过就本方案而言，风险似乎相对较小——让这些航天器保持在原位反而比让它们被（太阳）风吹散更费劲。一旦它们漂离拉格朗日点，就不再是问题，损失的只是发射的钱和材料。相比我听过的其他方案，这个看起来安全得多。

godshatter查看英文原文

I'm not against geo-engineering as a general concept, even though I don't personally buy into the most alarmist of the climate change scenarios. If we do do some kind of project like this, I would want to have a counter in place in case it does more harm than good, as a general rule of thumb. I would want that factored into the cost and preparations in place for just such an eventuality before committing to such a course. In this case, though, it seems relatively trivial - it seems like it's more work to keep them in place then to have them scatter to the (solar?) winds. Once they've moved out of the Lagrange point, then they become a non-issue. All we've lost is the money to put them there and the materials. Compared to some of the other ideas I've heard, this appears to be much safer.

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利用内拉格朗日点附近的小航天器云团为地球降温

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