20240910|气候变化会影响人类的生育能力吗？

The hottest year on record, 2023, may not retain its title for long; 2024 already looks as though it may overtake it.

2023年是有记录以来最热的一年，但这个头衔可能不会保持太久；2024年似乎已经可能超过它。

As temperatures continue to rise, countries will scramble to prevent heat deathsand tackle extreme weather.

随着气温持续上升，各国将争相防止高温死亡并应对极端天气。

But global warming also has much subtler effects-including, researchers suggest, on fertility.

但研究人员认为，全球变暖也有更微妙的影响，例如对生育能力的影响。

A paper recently published in Population Studies, a journal, is the latest to document a relationship between extreme heat and babymaking.

最近发表在《人口研究》杂志上的一篇论文是最新一篇记录极端高温与生育之间关系的论文。

It showed that the fertility rate in Spain fell roughly nine months after extremely hot days, echoing recent data from countries around the world.

研究显示，西班牙的生育率在极端高温天气出现约9个月后下降，这与世界各国最近的数据相呼应。

Although this effect is generally small, it could grow as climate change accelerates.

虽然这种影响通常很小，但随着气候变化的加速，它可能会加剧。

Risto Conte Keivabu from the Max Planck Institute for Demographic Research in Germany, the lead author of the latest paper,

这篇最新论文的主要作者、德国马克斯·普朗克人口研究所的Risto Conte Keivabu

worked with his colleagues to calculate Spain's total fertility rate (TFR), the average number of children a woman is expected to have over her lifetime, based on current fertility rates, for each month between 2010 and 2018.

与同事合作，计算了2010年至2018年期间每个月西班牙的总生育率(TFR)，即根据目前的生育率，一名妇女一生中预计生育的平均子女数。

They then made use of Spanish weather data to see how the TFR varied with temperature.

然后，他们利用西班牙的天气数据来观察TFR如何随温度变化。

They found a clear drop in the TFRnine months after days with average temperatures between 25-30°C.

他们发现，在平均气温在25-30°C之间的九个月后，TFR明显下降。

The reduction was small but consistent, amounting to about 0.3% (equivalent to around 85 fewer babies) for each such day in a month.

降幅虽小，但很稳定，每月每增加一天，TFR就会减少约0.3%（相当于减少约85名婴儿）。

The effect increased with temperature: for each extra day above 30°C, the drop was closer to 0.8%. Weather and fertility have long been linked.

随着温度的升高，这种影响会加剧：每增加一天超过30°C，降幅就会接近0.8%。天气和生育能力长期以来一直息息相关。

For one thing, human births show seasonal patterns indicating conception more regularly occurs during colder periods.

首先，人类的生育表现出季节性模式，表明受孕更经常发生在较冷的时期。

But this new research joins a string of recent papers reporting slumps in birth rates following spikes in daily mean temperature around the world.

但这项新研究加入了最近一系列报告，这些报告称，随着全球日平均气温飙升，出生率会下降。

As such heat shocks are temporary, this does not imply the hottest countries will necessarily have the lowest average birth rates.

由于这种热冲击是暂时的，这并不意味着最热的国家必然拥有最低的平均出生率。

In America over 70 years of data show that a day above roughly 27°C produces an average 0.4% drop in the birth rate (equivalent to 1,150 babies) nine months later, relative to a mild day.

在美国，70多年的数据显示，与温和的天气相比，气温超过27°C的一天会导致9个月后的出生率平均下降0.4%（相当于1150名婴儿）。

Other, broadly similar, effects have been reported in South Korea, Brazil and sub-Saharan Africa.

韩国、巴西和撒哈拉以南非洲也报告了其他大致类似的影响。

In March Tamas Hajdu of the HUN-REN Centre for Economic and Regional Studies in Hungary reported a Europe-wide decrease in the birth rate of 0.7% for every additional day above 25°C. What is going on?

3月，匈牙利HUN-REN经济和区域研究中心的Tamas Hajdu报告称，每超过25°C一天，欧洲的出生率就会下降0.7%。这是怎么回事？

One possibility is that, as Cole Porter observed, people are disinclined to play their favourite sport when the weather is sizzling hot.

一种可能性是，正如科尔·波特（Cole Porter）所观察到的，当天气炎热时，人们不愿意进行他们最喜欢的运动。

This is borne out by a slight rebound across all studies in the months following a dip in either birth rate or TFR, suggesting some conception is merely postponed. But the data reveal there is more to it.

在出生率或总生育率下降后的几个月内，所有研究都出现了轻微反弹，这证明了这一点，表明一些受孕只是被推迟了。但数据显示，情况还不止于此。

In 2022 Dr Hajdu published a paper with his brother, Gabor Hajdu, at the HUN-RENCentre for Social Sciences, which tracked Hungary's conception rate as a function of weather.

2022年，Hajdu博士及其兄弟Gabor Hajdu在匈牙利社会科学中心发表了一篇论文，追踪了匈牙利受孕率与天气的关系。

Because they had access to weekly pregnancy data, rather than just the monthly birth rate, they were able to get a more fine-grained picture.

由于他们可以访问每周的怀孕数据，而不仅仅是每月的出生率，因此他们能够获得更细致的图像。

They found that pregnancies were not much less likely on hot days versus cool ones-the dip came around two weeks later.

他们发现，炎热天气的怀孕可能性并不比凉爽天气低多少——下降发生在大约两周后。

That could suggest a slow-acting physiological mechanism is responsible. If so, it is likely to involve sperm.

这可能表明一种缓慢作用的生理机制是造成这种情况的原因。如果是这样，很可能与精子有关。

Animal studies have shown pronounced but temporary drops in sperm count and quality after experimentally induced heat shocks.

动物研究表明，在实验诱导的热冲击后，精子数量和质量明显会暂时下降。

Crucially, those effects emerged gradually a few weeks after the heat exposure ended.

至关重要的是，这些影响在高温暴露结束几周后逐渐显现。

Another study has shown similar results in humans, with heat stress leading to reduced sperm quality and mobility two to eight weeks later.

另一项研究也表明，人类也存在类似的结果，热应激会导致精子质量和活力在两到八周后下降。

Whatever the cause, the effect of heat on fertility rates appears to be modest, and goes on to be partly reversed.

无论原因是什么，高温对生育率的影响似乎不大，而且会部分逆转。

For now, says Dr Keivabu, social, cultural and economic trendsare more important.

Keivabu博士说，目前，社会、文化和经济趋势更为重要。

As global warming bites deeper, Dr Hajdu speculates, even hotter summers might heighten the effect or else prolong its impact. All this may be another argument for air-conditioning.

Hajdu博士推测，随着全球变暖的影响越来越深，更热的夏天可能会加剧这种影响，或者延长其影响。所有这些可能都是空调的另一个理由。

In the American study, which included data from as far back as 1931, heat's impact on fertility began to lessen in the 1970s as air-conditioning was more widely adopted. "Netflix and chill" may need to re-enter the lexicon.

在美国的研究中，数据最早可以追溯到1931年，随着空调的普及，高温对生育率的影响在20世纪70年代开始减弱。“Netflix and chill”可能需要重新录入词典。