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Scientists Have Uncovered a Disturbing Climate Change Precedent

科学家发现了一个令人不安的气候变化先例



They were strange days at the beginning of the age of mammals. The planet was still hungover from the astonishing disappearance of its marquee superstars, the dinosaurs. Earth’s newest crater was still a smoldering system of hydrothermal vents, roiling under the Gulf of Mexico. In the wake of Armageddon our shell-shocked ancestors meekly negotiated new roles on a planet they inherited quite by accident. Before long, life settled into new rhythms: Earth hosted 50-foot-long boas sliding through steam-bath jungles, birds grew gigantic in imitation of their dearly departed cousins, and mildly modern mammals we might squint to recognize appeared. Within a few million years, loosed from under the iron heel of the vanished giants, they began to experiment. Early whales pranced across a Pakistani archipelago on all fours, testing out life in the water. The first lemur-like primates leapt from the treetops, and hoofed things of all varieties dashed through the forest.

哺乳动物时代开始的时候颇为奇怪。这颗行星仍然被它的超级巨星——恐龙令人震惊的消失搞的晕晕乎乎的。地球上最新形成的陨石坑仍然是一个正在冒烟的热液喷口系统,它在墨西哥湾的海底翻滚着。在世界末日之后,我们饱受惊吓的祖先们温顺地在他们所继承的星球上通过谈判获得了新的角色。不久之后,生命就按照新的节奏开始生活:地球上出现了在仿若进行桑拿浴的丛林中穿行的50英尺长的蟒蛇,鸟类在模仿它们的近亲的过程中开始变得巨大无比,而我们可能会忽略的现代哺乳动物也出现了。在几百万年的时间里,在那些消失的巨兽的铁蹄下,它们开始进行各种实验。早期的鲸鱼四肢匍匐着地地生活在一个巴基斯坦群岛上,并前往水中测试生命发展的新方式。第一种类似狐猴的灵长类动物从树顶上跳了出来,各种各样的有蹄类动物则都冲进了森林中。

But the most striking feature of this early age of mammals is that it was almost unbelievably hot, so hot that around 50 million years ago there were crocodiles, palm trees, and sand tiger sharks in the Arctic Circle. On the other side of the blue-green orb, in waters that today would surround Antarctica, sea-surface temperatures might have topped an unthinkable 86 degrees Fahrenheit, with near-tropical forests on Antarctica itself. There were perhaps even sprawling, febrile dead zones spanning the tropics, too hot even for animal or plant life of any sort.

但哺乳动物时代早期最显著的特征是,它热得令人难以置信,以至于大约在5000万年前,在北极圈内都出现过鳄鱼、棕榈树和沙虎鲨。在地球的另一边,在今天环绕南极洲的水域中,海洋表面的温度可能已经超过了不可思议的86华氏度,在南极洲上甚至出现了近热带的森林。热带地区甚至遍布着大片炎热的死亡地带,它对任何种类的动物或植物来说都太热了。

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To study Earth’s past, scientists need good rocks to study, and fortunately for geologists and fossil-fuel companies alike, the jungles and swamps of this early age of mammals left behind lots of coal. The Powder River Basin in the United States, for instance, is filled with fossil Paleocene swamplands that, when burned today, contribute about 10 percent of U.S. carbon emissions. Naafs’ team studied examples of lower-quality coals called lignites, or fossilized peat. They had been collected around the world (everywhere from open-pit coal mines in Germany to outcrops in New Zealand), and spanned the late-Paleocene and early-Eocene epochs, from around 56 to 48 million years ago. They were able to reverse engineer the ancient climate by analyzing temperature-sensitive structures of lipids produced by fossil bacteria and archaea living in these bygone wetlands, and preserved for all time in the coal. The team found that, under this past regime of high CO2, in the ancient U.K., Germany, and New Zealand, life endured mean annual temperatures of 23–29 degrees Celsius (73–84 degrees Fahrenheit) or 10–15 degrees Celsius (18–27 degrees Fahrenheit) warmer than modern times.

为了研究地球的过去,科学家需要对好的岩石材料加以研究,幸运的是,对于地质学家和化石燃料公司来说,哺乳动物时代早期的丛林和沼泽留下了大量的煤炭。例如,美国的粉河盆地便满是古新世时期的沼泽地,它贡献了美国如今约10%的碳排放量。Naafs的团队研究了被称为褐煤或泥炭化石的低质煤的样本。它们是从世界各地收集而来的(从德国的露天煤矿到新西兰的露头岩层),样本跨越了古新世晚期和始新世时期,从大约56亿一直到4800万年前。他们能够通过分析生活在这些过去的湿地中的化石细菌和古生菌所产生的并在煤炭中保存下来的脂质结构来重构古代气候。研究小组发现,在过去的高二氧化碳排放体系下,古代英国、德国和新西兰的年平均气温达到了23到29摄氏度(73到84华氏度),比现代当代的气温高出了10到15摄氏度(18到27华氏度)。

“These wetlands looked exactly how only tropical wetlands look at present, like the Everglades or the Amazon,” Naafs says. “So Europe would look like the Everglades and a heat wave like we’re currently experiencing in Europe would be completely normal. That is, it would be the everyday climate.”

Naafs说:“这些湿地看起来就是热带湿地的样子,就像大沼泽地和亚马逊河一样。所以欧洲看起来就像大沼泽地,像我们现在在欧洲所经历的热浪在那个时候是完全正常的。也就是说,这是日常气候。”

That modern European heat wave has, in recent weeks, sent sunbathing Scandinavians and reindeer to the beach in temperatures topping 90 degrees Fahrenheit in the Arctic Circle. It has also ignited devastating wildfires across Greece and triggered an excruciating weekend for Spain and Portugal. But over 50 million years ago this would have been the baseline from about 45 to 60 degrees latitude. Under this broiling regime, with unprecedented heat as the norm, actual heat waves might have begun to take on an unearthly quality.

最近几周,现代欧洲的热浪让北极圈内的斯堪的纳维亚人和驯鹿经受了90华氏度的高温。它还在希腊各地引发了毁灭性的森林大火,并导致了西班牙和葡萄牙令人痛苦的周末时光。但在5000多万年前,这却是北纬45到60度地区的基本状况。在这种令人难以置信的高温下,真正的热浪可能已经开始呈现出一种神秘的特质。

“Perhaps a heat wave in Europe would be something like 40 degrees Celsius (104 degrees Fahrenheit) for three weeks. We don’t know.” So that was life in the late Paleocene and early Eocene in the high mid-latitudes. But closer to the equator in this global sweat lodge, the heat might have been even more outrageous, shattering the limits of complex life. To see exactly how hot, Naafs’ team also analyzed ancient lignite samples from India, which would have been in the tropics at the time—that subcontinent still drifting across the Indian Ocean toward its eventual mountain-raising rendezvous with Asia. But unfortunately, the temperatures from these samples were maxed out. That is, they were too hot for his team to measure by the new methods they had developed. So it remains an open question just how infernal the tropics became in these early days of our ancestors, but some computers tasked with recreating this planet spit out the stuff of science fiction.

“也许欧洲的热浪会在三周内达到40摄氏度(104华氏度)。我们不知道。”这就是上新世晚期和中新世早期的生活。但是,在这个全球性的“蒸笼”中,更接近赤道的地方,温度可能会高得更加离谱,它超过了复杂生命体的生存极限。为了准确地观察到当时到底有多热,Naafs的团队还分析了来自印度的古褐煤样品,当时印度仍位于热带地区——这一板块仍在印度洋上漂移,并最终与亚洲板块会合。但不幸的是,这些样本所显示的温度是最高的。也就是说,它们太热了,以至于他的团队无法用他们开发的新方法来加以衡量。所以,在我们的祖先生存的早期阶段,热带地区是怎么变成这样的,仍然是一个悬而未决的问题,但是一些负责重构这个星球的计算机却得出了科幻小说里才会出现的场景。

“Some climate models suggest that the tropics just became a dead zone with temperatures over 50 degrees Celsius (122 degrees Fahrenheit) like in Africa and South America,” says Naafs. “But we have no data so we don’t know.”

Naafs说:“一些气候模型表明,热带地区变成了一个死亡地带,气温超过50摄氏度(122华氏度),就像非洲和南美洲一样,但我们没有相关数据,所以我们不知道。”

Naafs’ work fits into a larger developing picture of Earth as an almost unrecognizable greenhouse planet of the distant past. University of Colorado paleontologist Jaelyn Eberle recently returned to her office in Boulder from Ellesmere Island, in the Canadian High Arctic, where she’s been doing research since the 1990s. Ellesmere is as far north as you can get before you fall off North America and run into Père No?l drifting over pack ice. Here, featureless highlands overlook ice-choked fjords and a lone Peary’s caribou might mingle with a dozen musk oxen under a vast Nunavut sky. There are also polar bears, but Eberle luckily hasn’t had any run-ins so far—though perspective can play tricks on you at the top of the world, and a snow-white artic hare on its hind legs at the appropriate distance can appear threatening enough.

Naafs的工作与在遥远的过去作为一颗几乎无法被认出来的温室行星的地球的更大发展图景相吻合。科罗拉多大学的古生物学家Jaelyn Eberle最近回到了位于加拿大高北极地区埃尔斯米尔岛的办公室中,她从20世纪90年代就在此地开始了从事相关研究工作。埃尔斯米尔是你在离开北美大陆之前所能抵达的最北部地区。在这里,毫无特色的高地俯瞰着冰雪覆盖的峡湾,而一只孤独的皮里驯鹿可能会在广阔无垠的努勒维特天空下与十几只麝牛混杂在一起。这里还有北极熊,但幸运的是,Eberle到目前为止还没有遇到过任何的争端——尽管位于世界之巅的你的视角可能会捉弄你,在适当的距离上,一只出现在它后腿方的雪白的野兔也会显得很有威胁。

“You pick up your gun and get all nervous and worried and then look through your binoculars ... It’s just a rabbit,” says Eberle.

Eberle说:“你拿起你的枪,紧张而焦虑,然后透过你的双筒望远镜看过去……发现这只是一只兔子”。

But Eberle isn’t venturing this far north just for the occasional hair-raising encounter with polar wildlife. Her target is warmer-weather fauna. Though there are no trees here at the top of the world, there are tree stumps. And they are around 50 million years old.

但是,Eberle并不是在这个遥远的北方地区冒险,或者是为了偶尔与极地野生动物发生令人毛骨悚然的遭遇。她的目标是生活在更温暖气候下的动物群。虽然在这个世界之巅上没有树存在,但却有树桩。它们大约有5000万年的历史了。

“The fossil forests on Ellesmere are spectacular,” Eberle says about the ecosystem entombed in the arctic soils. “You start really looking into them and you go, ‘Wow. We are dealing with a rainforest.’”

“埃尔斯米尔的化石森林非常壮观,”埃伯利谈到了在北极土壤中埋藏的生态系统,“如果你开始认真地研究它们,然后你就会说,哇,我们碰到的是热带雨林。”

Eberle is a vertebrate paleontologist and though there’s the aforementioned odd musk ox passing by her camp to consider, in the rocks below she has her pick of animals to study.

Eberle是一名研究脊椎动物的古生物学家,尽管有前面提到的奇怪的麝牛经过她的营地,但她却是从下方的岩层里挑选动物来进行研究。

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One obvious way to reconcile this disparity is by noticing that the changes to the ancient earth took place over hundreds-of-thousands to millions of years and (IPCC graphs notwithstanding) that time won’t stop at the end of the 21st century. The changes that we’ve already set in motion, unless we act rapidly to countervail them, will similarly take millennia to fully unfold. The last time CO2 was at 400 ppm (as it is today) was 3 million years ago during the Pliocene epoch, when sea levels were perhaps 80 feet higher than today. Clearly the climate is not yet at equilibrium for a 400-ppm world.

一个调和这种差异的显而易见的颁发就是注意到发生在成百上千万年前的这种古代地球变化是不会在21世纪末停止的。我们已经引发的这些变化——除非我们迅速采取行动来抵消它们——同样也需要数千年才能完全展开。上一次二氧化碳浓度达到万分之四(就像今天这样)是在300万年前的上新世时期,当时的海平面可能比现在高80英尺。显然,对于一个二氧化碳浓度达到万分之四的世界来说,气候还没有达到平衡点。

And it won’t be for quite some time. And anyway, we’re clearly not content to stop at just 400 ppm. If we do, in fact, push CO2 up to around 1,000 ppm by the end of the century, the warming will persist and the earth will continue to change for what, to humans, is a practical eternity. And when the earth system finally does arrive at its equilibrium, it will most likely be in a climate state with no analog in the short evolutionary history of Homo sapiens. Most worryingly, the climate models that we depend on as a species to predict our future have largely failed to predict our sultry ancient past. And though the gulf is narrowing, and models are catching up, even those that come close to reproducing the hothouse of the early Eocene require injecting 16 times the modern level of CO2 into the air to achieve it—far beyond the rather meager doubling or tripling of CO2 indicated by the rock record.

而且这不会需要很长一段时间。无论如何,我们显然不满足于只停留在万分之四的浓度。事实上,如果我们真的让二氧化碳浓度在本世纪末被推高到千分之一,那么全球变暖将会持续,地球将继续发生改变,对人类来说,这是一个永恒的过程。当地球系统最终达到它的平衡时,它很可能处于一个在智人的短暂进化历史中没有出现过的气候状态中。最令人担忧的是,我们赖以预测未来的气候模型在很大程度上未能预测到我们闷热的古代历史。尽管这种差距正在缩小,而模型研究正在迎头赶上,甚至根据岩石的记录,那些接近于重构出始新世早期温室环境的模型需要往空气中注入比现有水平高出16倍的二氧化碳来实现这一指标。

Clearly we are missing something, and Naafs thinks that one of the missing ingredients in the models is methane, a powerful greenhouse gas which might help close the divide between model worlds and fossil worlds.

显然,我们忽略了一些东西,而Naafs认为模型中缺失的一种成分是甲烷,一种强大的温室气体,它可能有助于缩小模型世界和化石世界之间的差距。

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“If we were to burn all the fossil fuels and wait a few centuries we might return to this,” he says. “Basically every type of paleoclimate research that’s being done shows that high CO2 means that it’s very warm. And when it gets very warm, it can be really, really, really warm.”

他说:“如果我们烧掉了所有的化石燃料,那么等上几个世纪,我们可能会回到这个环境中。基本上可以说,每一种类型的古气候研究都表明,高浓度的二氧化碳意味着非常温暖。当它变得非常温暖的时候,那就是真的很温暖了。”