全球变暖，比我们预想的更严重
人们发现，全球变暖的规模可能是之前预测值的两倍，这个结论是基于过去对温暖期的研究得出的。
Future global warming may eventually be twice as warm as projected by climate models and sea levels may rise six metres or more even if the world meets the 2°C target, according to an international team of researchers from 17 countries.
一个由17个国家的研究人员组成的研究小组称，即使世界实现了“2摄氏度”目标，全球变暖可能是预测模型的两倍，海平面也会上升不止六米。(“2摄氏度阈值”说是欧盟率先提出来的。其内容是，相对于1750年工业化前的水平，全球平均气温升高2摄氏度是人类社会可以容忍的最高升温，并由此引发出，为确保到本世纪末全球升温不超过这个阈值，则全球在2050年以前必须将温室气体排放在1990年的基础上至少减少50%，即所谓全球排放减半。)
The findings published last week in Nature Geoscience are based on observational evidence from three warm periods over the past 3.5 million years when the world was 0.5°C-2°C warmer than the pre-industrial temperatures of the 19th Century.
这项研究已经发布在上周的《Nature Geoscience》上：据过去350万年的三个温暖期的观测证据，这几个时期的世界温度比19世纪前工业化时期水平高0.5-2摄氏度不等。
The research also revealed how large areas of the polar ice caps could collapse and significant changes to ecosystems could see the Sahara Desert become green and the edges of tropical forests turn into fire dominated savanna.
该研究还表明，极地冰盖可能会大面积崩溃，生态系统的重大变化可能会让撒哈拉沙漠变成绿洲，而热带森林的边缘之处也成了稀树草原。(稀树草原是炎热、季节性干旱气候条件下长成的植被类型，其特点是底层连续高大禾草之上有开放的树冠层，即稀疏的乔木。世界最大片的稀树草原见于非洲、南美洲、澳大利亚、印度、缅甸 -泰国地区和马达加斯加。)
"Observations of past warming periods suggest that a number of amplifying mechanisms, which are poorly represented in climate models, increase long-term warming beyond climate model projections," said lead author, Prof Hubertus Fischer of the University of Bern."This suggests the carbon budget to avoid 2°C of global warming may be far smaller than estimated, leaving very little margin for error to meet the Paris targets."
来自伯恩大学的第一作者休伯特斯 · 费希尔教授说：“对过去变暖期的观察表明，气候模型中代表性较差的一些放大机制，揭示了我们可能会经历长时间的温暖期，这在当初天气模型的预测之外。而这就意味着，因为之前估计错误，所以2摄氏度目标难以实现，而《巴黎协定》的误差就得另当别论了。”
To get their results, the researchers looked at three of the best-documented warm periods, the Holocene thermal maximum (5000-9000 years ago), the last interglacial (129,000-116,000 years ago) and the mid-Pliocene warm period (3.3-3 million years ago).
为了得出结论，研究人员观察了三个记录最佳的温暖期，分别是全新世(5000 - 9000年前)、最后一次间冰期(129000 - 116000年前)和上新世中期暖期(330- 300)万年前。
The warming of the first two periods was caused by predictable changes in the Earth's orbit, while the mid-Pliocene event was the result of atmospheric carbon dioxide concentrations that were 350-450ppm – much the same as today.
前两个时期的变暖是由地球轨道变化引起的，这在我们的预料之中，而上新世中期变暖则是因为大气中二氧化碳浓度已经达到了350-450ppm。
Combining a wide range of measurements from ice cores, sediment layers, fossil records, dating using atomic isotopes and a host of other established paleoclimate methods, the researchers pieced together the impact of these climatic changes.In combination, these periods give strong evidence of how a warmer Earth would appear once the climate had stabilized. By contrast, today our planet is warming much faster than any of these periods as human caused carbon dioxide emissions continue to grow. Even if our emissions stopped today, it would take centuries to millennia to reach equilibrium.
研究人员对冰芯、沉积物层、化石记录进行了研究，利用原子同位素测量和大量其他的测量方式，并对结果进行了综合性考量，最后得出：这些时期已经足以说明，一旦气候稳定下来，地球将会变得很“温暖”。 相比之下，今天的地球的变暖速度比以上任何一个时期都快，因为二氧化碳排放量仍在持续增长。 即使我们在今天就停止排放，地球也需要几个世纪甚至是几千年才能达到平衡。
The changes to the Earth under these past conditions were profound – there were substantial retreats of the Antarctic and Greenland ice sheets and as a consequence sea-levels rose by at least six metres; marine plankton ranges shifted reorganising entire marine ecosystems; the Sahara became greener and forest species shifted 200 km towards the poles, as did tundra; high altitude species declined, temperate tropical forests were reduced and in Mediterranean areas fire-maintained vegetation dominated.
过去，地球发生了一系列的重大变化——南极和格陵兰冰原大量退缩，因此海平面至少上升了6米; 海洋浮游生物使得整个海洋生态系统重组; 撒哈拉绿色区域更多了，森林物种向两极移动200公里，苔原也不例外; 高海拔物种减少，温带热带森林减少，地中海地区也是以可烧林火的植被为主。
"Even with just 2°C of warming – and potentially just 1.5°C – significant impacts on the Earth system are profound," said co-author Prof Alan Mix of Oregon State University. "We can expect that sea-level rise could become unstoppable for millennia, impacting much of the world's population, infrastructure and economic activity."
俄勒冈州立大学的艾伦 · 米克斯教授是论文的合著者，她说:”不说2摄氏度，哪怕只有1.5摄氏度，对地球的影响也是巨大的。可以想见，在未来的千年之内，我们都无法阻止海平面上升，这对世界的人口、基层建筑、经济活动都有影响。”
Yet these significant observed changes are generally underestimated in climate model projections that focus on the near term. Compared to these past observations, climate models appear to underestimate long term warming and the amplification of warmth in Polar Regions.
然而，在气候模型预测中，我们通常低估了这些重大的观测变化，因为之前的预测往往集中短期时间内的变化。与过去的观测结果相比，气候模型似乎低估了长期变暖效应，也忽视了极地地区的升温。
"Climate models appear to be trustworthy for small changes, such as for low emission scenarios over short periods, say over the next few decades out to 2100. But as the change gets larger or more persistent, either because of higher emissions, for example a business-as-usual-scenario, or because we are interested in the long term response of a low emission scenario, it appears they underestimate climate change," said co-author Prof Katrin Meissner, Director of the University of New South Wales Climate Change Research Centre."This research is a powerful call to act. It tells us that if today's leaders don't urgently address our emissions, global warming will bring profound changes to our planet and way of life – not just for this century but well beyond."
合著者新南威尔士大学气候变化研究中心主任、卡特琳·迈斯纳教授说：“气候预测模型在预测小型变化时，还是可信的，比如短期内(类似于从现在起到2100年)的低排放。不论是因为碳排放量持续增加，还是因为现在固有的商业模式，我们都低估了长远影响。而现在，这项研究就是一个强有力的号召。它告诉我们，如果今天不迫切地解决排放问题，全球变暖将给我们生存之地以及生活方式带来重大变化，而且这种变化也不仅仅只影响我们这一个世纪。”
