The global public health emergency involving deformed¹ babies emerged in 2015, the hottest year in the historical record, with an outbreak in Brazil of a disease transmitted by heat-loving mosquitoes. Can that be a coincidence?

2015年，全球出现了涉及婴儿畸形的公共卫生紧急情况。这一年也是有历史记录以来最热的一年。这种由喜热的蚊子所传播的疾病在巴西爆发，是否可能只是巧合？

Scientists say it will take them years to figure that out, and pointed² to other factors that may have played a larger role in starting the crisis. But these same experts added that the Zika epidemic³, as well as the related spread of a disease called dengue that is sickening as many as 100 million people a year and killing⁴ thousands, should be interpreted as warnings.

科学家称，要确定是否属于巧合需要进行多年的研究。他们指出这次危机可能另有原因。但是，这些专家还补充说，兹卡的疫情以及与之相关的登革热的传播应该被视为一种警告。后者一年最多能感染1亿人，并造成数以千计的人们死亡。

Over the coming decades, global warming is likely to increase the range and speed the life cycle of the particular mosquitoes carrying these viruses, encouraging their spread deeper into temperate⁵ countries like the United States.

在未来几十年，全球变暖可能造成那些携带这些病毒的特殊种类的蚊子的活动范围扩大和生命周期加快，进而促使这些疫病向美国等温带国家扩展。

Recent research suggests that under a worst-case scenario⁶, involving continued high global emissions⁷ coupled with fast population growth, the number of people exposed to the principal mosquito could more than double, to as many as 8 billion or 9 billion by late this century from roughly 4 billion today.

近期的研究表明，最糟糕的一种情况是，随着全球温室气体的大量排放和人口的高速增长，有可能接触这种蚊子的人口将翻番，目前是40亿左右，到本世纪末将多达80亿或90亿。

“As we get continued warming, it’s going to become more difficult to control mosquitoes,” said Andrew Monaghan, who is studying the interaction of climate and health at the National Center for Atmospheric⁸ Research in Boulder⁹, Colo. “The warmer it is, the faster they can develop from egg to adult, and the faster they can incubate viruses.”

“随着全球变暖，控制蚊子将越来越困难。”安德鲁·莫纳甘(Andrew Monaghan)说。安德鲁在科罗拉多州博尔德的美国国家大气研究中心(National Center for Atmospheric Research)研究气候与健康的互动关系。“天气越热，蚊子从孵化到成年的速度就越快，病毒繁殖的速度也就越快。”

Already, climate change is suspected — though not proven — to have been a factor in a string of disease outbreaks afflicting¹⁰ both people and animals. These include the spread of malaria¹¹ into the highlands of eastern Africa, the rising incidence of Lyme disease in North America, and the spread of a serious livestock¹² ailment¹³ called bluetongue into parts of Europe that were once too cold for it to thrive.

人们怀疑，气候变化是人畜感染一系列疾病的一个原因，尽管这一点尚未得到证实。这些疾病包括东非高原地区的疟疾，北美莱姆病的发病率升高，欧洲部分地区的牲畜出现的严重的蓝舌病疫情，那些地区之前因为太冷，很少出现这些疾病。

In interviews, experts noted¹⁴ that no epidemic was ever the result of a single variable.

在访谈中，专家指出没有任何一种传染病是仅由一个变量引起的。

Instead, epidemics¹⁵ always involve interactions among genes¹⁶, ecology, climate and human behavior, presenting profound difficulties for scientists trying to tease apart the contributing factors. “The complexity¹⁷ is enormous,” said Walter J. Tabachnick, a professor with the Florida Medical Entomology Laboratory, a unit of the University of Florida in Vero Beach.

相反，传染病常常涉及基因、生态、气候、人类行为等多种因素的互动，所以科学家很难把单个因素分离出来。“原因极为复杂。”佛罗里达大学(University of Florida)位于维罗比奇(Vero Beach)的佛罗里达医学昆虫学实验室的教授瓦尔特·塔巴奇尼克(Walter J. Tabachnick)说。

The epidemics of Zika and dengue are cases in point. The viruses are being transmitted largely by the yellow fever mosquito, Aedes aegypti. That creature adapted long ago to live in human settlements, and developed a concomitant taste for human blood.

兹卡和登革热就是典型的例子。这些病毒主要是由感染黄热病的伊蚊传播。这种生物早已适应了在人类聚居地生存，并因此喜好人类的血液。

Cities in the tropics, the climate zone most favorable to the mosquito, have undergone explosive growth: Humanity passed a milestone¹⁸ a few years ago when more than half the population had moved to urban areas. But spending on health care and on basic public health infrastructure¹⁹, like water pipes and sewers²⁰, has not kept pace. Mosquito control has also faltered²¹ in recent decades.

热带是最适合蚊子生存的气候带，而那里的城市正在经历迅猛的增长：几年前人类就跨过了一个里程碑：一半以上的人口已迁居到城市地区。但是公共医疗和公共卫生基础设施的投入，比如水管和下水设施，仍是滞后的。近几十年对蚊子的控制也出现了放松。

The mosquito lays its eggs in containers of water, of a sort that are especially common in the huge slums of Latin American cities. With unreliable access to piped water, people there store water in rooftop cisterns²², buckets and the like. Old tires and other debris²³ can also become mosquito habitat.

蚊子在盛水的容器中产卵，这种容器在拉丁美洲城市的大型贫民窟中尤其常见。由于没有可靠的管道用水，那里的人们会把水存放在屋顶的水箱、水桶和类似的容器中。旧轮胎和其他垃圾也可能成为蚊子的栖息地。

Water storage near homes is commonplace in areas where Zika has spread rapidly, like the cities of Recife and Salvador in northeastern Brazil, and where dengue experienced a surge in 2015, like S漀 Paulo, Brazil’s largest state.

在兹卡病毒迅速传播的区域，比如巴西东北部城市累西腓和萨尔瓦多，以及2015年出现登革热病例激增的巴西最大州圣保罗，都有在民宅附近存水的习惯。

Altogether, dengue killed at least 839 people in Brazil in 2015, a 40 percent increase from the previous year. Worldwide, dengue is killing more than 20,000 people a year.

2015年，巴西共有至少839人死于登革热，比上一年增加40%。而全世界一年有超过2万人死于登革热。 多名专家在访谈中称，疾病爆发的一个主要原因很可能是城市化、人口增长和跨国旅行造成受风险人口增加。他们认为气候变化只是压垮骆驼的最后一根稻草。

Several experts said in interviews that a main reason for the disease outbreaks was most likely the expansion of the number of people at risk, through urbanization, population growth and international travel. They see the changing climate as just another stress on top of a situation that was already rife²⁴ with peril²⁵.

多名专家在采访中说，疾病爆发的一个主要原因很可能是随着城市化、人口增长和跨国旅行，面临风险的人群扩大了。他们认为在已经有重重危险的局面中，气候变化只是其中的一重压力。

While they do not understand to what degree rising temperatures and other weather shifts may have contributed to the outbreaks, they do understand some of the potential mechanisms²⁶.

虽然他们并不知道气温升高和其他气候变化因素，对疫情爆发的作用有多大，但是他们明白其中一些潜在的机制。

The mosquitoes mostly live on flower nectar, but the female of the species needs a meal of human blood to have enough protein to lay her eggs. If she bites a person infected with dengue, Zika or any of several other diseases, she picks up the virus.

蚊子大多以花蜜为生，但是雌性蚊子为了产卵，需要吸人血来提供充足的蛋白质。如果它叮了已感染登革热、兹卡或其他几种病的人，它就携带了该种病毒。

The virus has to reproduce in the mosquito for a certain period before it can be transmitted to another person in a subsequent bite. The higher the air temperature, the shorter that incubation period. Moreover, up to a point, higher temperatures cause the mosquitoes to mature faster.

病毒需要在蚊子的体内繁殖一段时间，才能在下一次叮咬时传播给他人。温度越高，病毒繁殖所需的时间就越短。而且在某个限度以内，温度越高，蚊子的成熟就越快。

With rising temperatures, “You’re actually speeding up the whole reproductive cycle of the mosquitoes,” said Charles B. Beard, who heads a unit in Fort Collins, Colo., studying insect-borne diseases for the Centers for Disease Control and Prevention in Atlanta. “You get larger populations, with more generations of mosquitoes, in a warmer, wetter climate. You have this kind of amplification²⁷ of the risk.”

温度上升“实际上会加速蚊子的整个繁殖周期，”查尔斯·B·彼尔德(Charles B. Beard)说，“人口增加了，在更潮湿、更炎热的气候里，存活的蚊子世代也增多了，这就放大了风险。”彼尔德领导着一个位于科罗拉多州科林斯堡的团队，为亚特兰大的疾病控制与预防中心(Centers for Disease Control and Prevention in Atlanta)进行昆虫传播疾病研究。

In principle, the risk from continued global warming applies not just to temperate countries, but to cities at high altitude in tropical countries. Researchers are keeping a close eye on Mexico City, for instance.

理论上，全球持续变暖所带来的风险，不仅涉及温带国家，还涉及热带国家的高海拔城市。比如，研究人员正在密切关注墨西哥城。

With 21 million people in the city and its suburbs, Mexico City is the largest metropolis²⁸ of the Western Hemisphere. While the lowlands of Mexico are plagued by yellow fever mosquitoes and the viruses they transmit, the country’s capital sits on a mountain plain that has — up to now — been too cold for the mosquitoes.

墨西哥城的城区和郊区一共有2100万人，它是西半球最大的都市。虽然在墨西哥的低地，感染黄热病和其他病毒的蚊子到处肆虐，但是墨西哥的首都位于较寒冷的山顶平原，至少目前蚊子还无法在那里生存。

But temperatures are rising, and the mosquitoes have recently been detected in low numbers near Mexico City.

但是随着气温的升高，墨西哥城附近最近发现了少量的蚊子。

“The mosquito is just down the hill, literally,” Dr. Monaghan said. “I think all the potential is there to have virus transmission if climatic conditions become a bit more suitable.”

“蚊子已经来到山脚下了，”莫纳甘博士说。“我觉得只要气候条件再合适一点，病毒就有可能开始传播。”