Is climate change the cause of extreme weather events? Until now the link has been suspected but never confirmed with scientific confidence. That position is now changing. A new study from the US confirms that for some extreme events there is a causal connection.

气候变化是极端天气事件的元凶吗？人们一直怀疑二者存在关联，但从来没有做出令人信服的科学证实。如今，这种情形正在发生变化。美国的一项新研究证实，气候变化与某些极端天气事件之间确实存在因果关系。

This link between climate science and immediate¹ weather conditions can only strengthen the case of those arguing for policy change. The impact of a damaging heatwave in terms of deaths, sickness and other social and economic costs is much more likely to rouse public opinion than the distant prospect² of what might to some sound like a modest increase in the global mean temperature. All politics are local, and they are also immediate. The discount rate applied³ to future possibilities is very high: what could happen to a future generation decades matters much less than what is happening to me here and now. It brings climate to the foreground and diminishes the argument of those who say that since we don’t know everything we should do nothing and wait until we see how things turn out. If the impact is immediate and people are dying as a result, the call for action will be loud.

气候科学与即时天气状况之间的这种关联，会让那些主张转变政策的人士更有底气。也许在一些人听起来，全球平均气温不过将略微升高，这样的前景显得很遥远，相比之下，破坏性热浪所造成的影响——致死、致病及造成其他社会和经济损失——更容易激发公众舆论。所有的政治都只顾本地和眼前。未来可能性的贴现率非常高：几十年后未来一代人可能遇到的事情，远没有我本人在当下、在此地所将面临的事情重要。上述关联使得气候问题备受关注，也削弱了持以下观点的人士的理由：既然我们并不知晓一切，我们应该什么都不做，直至看清事态发展的结果。如果说气候变化的影响是即时的，并且造成了人的死亡，那么要求行动的呼声将很高。

One of the most dangerous illusions in the debate around the implications of climate change is the notion that the impact will only be material when the carbon concentration in the atmosphere exceeds some defined limit — usually quoted as 450ppm. At that point global mean temperatures will rise by an average of 2 degrees centigrade and the problems will begin. I do appreciate that the science is much more complicated but I think this is how the challenge is seen by many non-expert policy makers⁴ and politicians.

在围绕气候变化影响的争论中，最危险的观念之一是认为只有当大气中的碳浓度超过某个明确的限度——通常引用的是450百万分率(ppm)——才会产生切实的影响。到那时，全球平均气温将上升2摄氏度，问题将开始出现。我当然知道气候科学要复杂得多，但我认为这正是许多非专家型的政策制定者和政治家看待气候挑战的态度。

That view is mistaken. It implies an accuracy in the knowledge of the relationship between carbon concentration and the effect on temperatures that doesn’t yet exist — not least because, as Martin Rees, the former President of the Royal Society puts it, we are conducting an experiment with the earth’s atmosphere which has never been tried before. We don’t know with any degree of certainty that 450ppm will produce an average rise of 2 degrees and we don’t know what the variations around that average figure might be across the world. The case for action is driven by the precautionary principle. But there is another known unknown and that is the extent and nature of the impact in the shorter term — before we get to 450ppm.

这种看法是错误的。它暗含这样一种意思，关于碳浓度与其对气温影响的关系，在我们所了解的知识中存在一种精确性。而实际上还不具有这样的精确性，主要是因为，正如英国皇家学会(Royal Society)前主席马丁•里斯(Martin Rees)所言，我们正在进行一项人类从未尝试过的地球大气实验。我们丝毫无法确定，450ppm的碳浓度是否将造成平均升温2摄氏度，我们也不知道在那个平均值上下世界各地可能出现什么变化。行动的理由是出于预防原则。但是还有另一个“已知的未知”，即在更短时期内（碳浓度达到450ppm之前）气候变化造成的影响的程度和性质。

A new and important study from the National Academy of Sciences in the US focuses on the impact of climate change and weather conditions and explores the vexed⁵ question of event attribution. Can we say that a heatwave in Paris — as occurred in the summer of 2003 killing⁶ some 3,000 people, and again last year, killing another 700 or floods on the Somerset levels in southwest England as in the winter of 2013/14 are the direct consequence⁷ of climate change? Did the wildfires that swept western Russia in the summer of 2010 killing some 56,000 people, according to the independent estimate of the insurance company result from global warming?

美国国家科学院(National Academy of Sciences)一项重要的新研究着眼于气候变化的影响和天气条件，并探索了极端天气事件归因这个棘手难题。我们可以说巴黎的热浪（2003年夏天造成约3000人死亡，去年又造成700人死亡）或者2013/14年冬天英格兰西南部萨默塞特郡的洪水是气候变化的直接后果吗？2010年夏天席卷俄罗斯西部、造成约5.6万人死亡（根据保险公司的独立估算）的野火是由全球变暖引起的吗？

Until now, the careful scientific answer has been that there may be a linkage⁸ but it cannot be proved. Now, however, the science of event attribution is changing that position. It is beginning to be possible to say that some weather events are directly linked and attributable to climate change. Events such as heatwaves fall within that category. For the moment, cyclones⁹ do not and nor do droughts because too many other factors are involved.

一直以来，谨慎的科学回答是：可能有关联，但无法证实。然而，如今，极端天气事件归因的科学正在改变这一情形。我们开始可以称一些天气事件与气候变化直接相关，或者是由气候变化造成的。热浪等事件就属于这一类。目前来看，飓风和干旱并不属于这一类，因为它们还牵涉到太多其他因素。

In the view of the authors of the NAS study, to justify¹⁰ attribution requires:

在上述NAS研究报告的作者们看来，证明极端天气事件归因需要满足以下几个标准：

- a long-term historical track record of data to set the context of any current event

-长期的数据跟踪历史记录，为当前所有天气事件建立背景

- the ability to simulate the events accurately¹¹ in climate models.

-能够在气候模型中精确模拟天气事件。

- a position purely¹² influenced by meterological data.

-一种只受气象数据影响的状况(position)。

- that there is an understood and robustly¹³ simulated physical mechanism¹⁴ that relates a given class of extreme events to long-term anthropogenic climate changes such as global-scale temperature increase or increases in water content of a warmer atmosphere.

-存在一个可理解的、可靠模拟的物理机制，将给定级别的极端天气事件与长期人为气候变化——比如全球范围的气温升高或变暖的大气中含水量的增加——联系起来。

For heatwaves these standards can be met.

热浪天气可以满足上述所有标准。

In areas where the standards cannot yet be met more work needs to be done — separating out the different factors involved in producing particular circumstances and showing what if any proportion of the outcome is due to climate change.

但对于还不能满足上述标准的领域，则需要进行更多工作，要分解出造成特定气象的各种有关因素，证明结果有多少是气候变化所致。

This is an important advance. We may not yet be at the point of being able to predict the frequency of extreme weather events — that is, we cannot say that there is likely to be a heatwave in Paris at least once every five years but we are close to being able to say that heatwaves are much more frequent than they have been in the past and that the change in frequency is due to a change in the climate.

这是一个重要的进步。我们可能暂时还无法预测极端天气事件的发生频率，也就是说，我们无法肯定巴黎是否至少每隔五年就出现一次热浪，但我们几乎能够肯定热浪比过去更为频繁，而这种频率变化是由于气候变化造成的。

As this linkage becomes more obvious the public demand for action will grow more intense and that in turn will raise a serious political problem. Even politicians who fully accept the risks of climate change cannot change the weather because heatwaves and other current extreme weather conditions are being caused by the change that has already occurred. Cutting carbon emissions¹⁵ to zero immediately — even if that were practical — would not alter the situation although it could, of course, prevent further deterioration¹⁶. Equally, countries cannot not isolate¹⁷ themselves. The weather does not recognise political boundaries. In such circumstances the only viable¹⁸ response is adaptation and the development of provision to cope with the increased risks. The approach is sensible but it can be expensive. Taking precautions against the risks of a heatwave is not a simple process.

随着这种关联变得越来越明显，公众将更加强烈地要求采取行动，这反过来将提出一个严重的政治问题。即使是完全同意气候变化风险的政治家也无法改变天气，因为造成热浪以及当前其他极端天气情况的原因，是已经发生的气候变化。就算能将碳排放立即减少到零也无法改变现状，当然，这可以防止情况进一步恶化。同样，各国无法独善其身，天气可不认识领土疆界。在这种情况下，唯一可行的对策就是去适应，以及制定预防措施，以应对不断增加的风险。此方法虽明智，但代价会很高，不过想要防范热浪风险本就不是个简单的过程。

In politics, if a risk cannot easily be removed or managed the temptation is to look for someone to blame. In legal terms this will be translated into the concept of liabilities. If you are a shareholder¹⁹ in an energy business you might like to ask your company’s view of the issue. It would be fascinating to read their responses.

政治方面，如果一个风险无法轻易被消除或管控，政治家很可能会寻找一个替罪羊。从法律上讲，这将转换成责任的概念。如果你是一个能源公司的股东，你可能会问公司对此问题的观点，看他们作何反应将是件有趣的事。