比起中美爆发地面战争这种小概率事件，气候变化对全球安全的威胁要严峻得多了。然而美国在2017年足足投入了5900亿美元的国防预算，为的只是打赢一场不太可能发生的大规模常规战争。美国的保守主义者是时候重新理解一下宪法序言中那句“建立共同国防”的含义，认真解决气候变化带来的日益严峻的挑战了。

保守派通常会祭出三大理由为面对气候变化的不作为辩护：第一，科学本身有一定的不靠谱性；第二，解决问题的成本太高，我们负担不起；第三，就算我们作为了，其他国家也会继续污染地球，所以我们就算行动了也没用。

第一：科学到底有几成靠谱？这并不重要。我们终归有义务保护国家安全，哪怕面临的威胁是不确定的。

近十几年来，美国情报和国防部门早已对气候变化问题敲响了警种，指出了它可能带来的潜在影响。

2017年，美国国防部长马蒂斯在一份未公开的书面证词中明确指出，气候变化对美国国家安全利益的威胁是现实的。

今年2月，美国情报部门发布了一份《世界威胁评估报告》。文中，美国国家情报总监丹尼尔·科茨坦承，气候变化有可能会造成人道主义灾难及冲突。同月，部门美军退役高官也发表了一份报告，详细指出了海平面升高造成的威胁，以及其对美国军队执行有关任务的可能影响。

以上言论表明，美国军方就此已经形成了共识：气候变化的威胁是真实的，其威胁程度是严峻的，即便它的影响在数字模型上仍存在一定的不确定性，我们也应立即采取行动对应对它。

第二：我们能负担得起成本吗？答案是肯定的。

未来几十年，美国预计将投入2万亿美元用于维护全国电网。要将现有电网升级成近乎零排放的现代化电网，则需要2万亿到3万亿美元。如果我们立即行动起来，或许我们不需要额外多花一分钱，就能在2万亿的框架里完成升级改造。

而相比之下，自从2001年以来，美国光是投在打仗上的钱，就达到了5.6万亿美元左右。

我们为什么就不能升级一下国内的基础设施呢？

我们已经拥有了在可接受的成本范围内对电力部门进行低碳化改造的技术。当然，要想对工商业和居民能源消费进行低碳化改造，挑战还是有的，但这些挑战大都是经济问题，而不是技术问题。

而美国应该做的，正是投资解决这些挑战。

第三：美国治不治理气候变化问题，是否应取决于其他国家对待排放的态度？答案是否定的。虽然这个担心不无道理，但“灯塔国”毕竟不是能白当的。过去几十年，全球的大洋航线都是美国领衔保护的，可以说这几十年来，其他国家都是在没有交“过路费”的情况下搭便车，但是美国也从这种领导角色中获取了大量利益。所以“搭便车”的问题并不是美国不作为的借口。

尽管军事威胁的时机和地点有很大的不确定性，但我们总是以万全之策准备打仗。对于气候变化，我们也应做好同样的万全准备。毕竟尽管气候变化对世界的影响范围仍有一定的不确定性，但是这种威胁是现实存在的，而且有可能带来灾难性的后果。

整个冷战期间，大西洋两岸的国家都能够积极地对本国进行投资，以应对日益提高的苏联威胁。当时我们修的高速公路大大便捷了现代人的生活，载人登月的壮举促进了后世多个科技领域的大发展，我们当时打下的教育基础，更是直接刺激了后来的计算机革命。

如果我们能采取同样的方式对科学技术进行投入，以打造一个低碳化的未来，那么我们很有可能也会获得同样的回报。

我们很难衡量国防投资的收益率，同样，我们也很难衡量应对气候变化投资的收益率。但不管怎样，依据宪法，联邦政府有义务保护美国免受各种威胁，不管它来自国外还是国内。（财富中文网）

本文作者Todd Davidson是德克萨斯州立大学奥斯汀能源研究所研究员。

译者：朴成奎

Climate change poses a more significant threat to global security than the low probability event of a ground war with China. And yet, we spent $590 billion on defensein 2017 and maintained readiness against the unlikely prospect of a large conventional war. It’s time for conservatives to recognize our constitutional mandate to provide for the common defense by addressing the rising threat of climate change.

There are three primary explanations that are used to justify inaction on climate change: The science is uncertain; we cannot afford to address the problem; and other counties will keep polluting, so our actions won’t matter.

First: Is the science settled? It does not matter—we have an obligation to be prepared to defend the country, even if the threat is uncertain.

For more than a decade, national intelligence and defense agencies have sounded the alarm on climate change and the potential impact it might have.

In 2017, in unpublished, written testimony, Secretary of Defense James Mattis stated in unequivocal terms that climate change is real and is a threat to national security interests.

In February, the U.S. intelligence community published its “Worldwide Threat Assessment.” In it, Daniel Coats, the director of national intelligence, acknowledged the potential for climate change to cause humanitarian disasters and conflict. That same month, a panel of retired military officers published a report detailing the threat of sea level rise and the potential to inhibit the U.S. military’s mission.

The concerns expressed by our military leaders have created a growing consensus: The threat of climate change is real, it poses a significant threat, and now is the time to act regardless of the uncertainty in modeling the impacts of climate change.

Second: Can we afford to act? Yes.

In the coming decades, we will collectively spend approximately $2 trillion to maintain our electrical grid. Upgrading the existing grid to a near-zero-carbon solution would cost approximately $2 trillion to $3 trillion. We could upgrade the grid without costing ourselves a penny more than the status quo if we start working now.

Compare the cost of upgrading our grid with the estimated $5.6 trillion we will have spent fighting wars since 2001.

Why are we unable to upgrade domestic infrastructure?

We already have the technology that could deliver an affordable, decarbonized electricity sector. Challenges remain to decarbonize industrial, commercial, and residential energy consumption, but most of these hurdles are economic challenges, not technological barriers.

Addressing these challenges is exactly what the United States should be investing in.

Third: Should emissions from other nations influence whether the United States works to address climate change? No. Although this concern is real, we should recognize that the U.S. has led the way on protecting naval shipping lanes around the world for decades. Other countries have arguably been free-riders throughout this time, but we are all better off for the leadership role that the United States has taken. The free-rider problem should not be an excuse for inaction.

Despite the uncertainty in the timing and location of military threats, we are always ready for war just in case. The same approach of readiness should be used for climate action, because despite the uncertainty in how climate change could impact the world, the threat on the horizon is real and has the potential to be catastrophic.

Throughout the Cold War, people from both sides of the aisle were able to support investment in domestic capabilities to counter the rising existential threat of the Soviet Union. We have now reaped immeasurable benefits from national highways, spin-offs from landing men on the moon, and helping set the educational foundation that led to the computer revolution.

We will likely reap similar rewards by investing in technologies that can deliver a decarbonized future.

It is hard to measure the return on investment for dollars invested in defense. It will also be hard to measure the return on investment for combating climate change. Nevertheless, the federal government has a constitutional mandate to defend the United States against threats, both foreign and domestic.

Todd Davidson is a research associate at the University of Texas at Austin Energy Institute.