“震耳欲聋”！联合国气候报告拉响生存警报
加州的大火还在熊熊燃烧。
联合国政府间气候变化专门委员会（IPCC）昨日发布了一份具有里程碑意义的气候变化报告，为人类拉响警报——人类活动正在以前所未有、甚至不可逆转的方式改变地球气候。
报告指出，除非未来几十年内大幅减少温室气体排放，否则全球变暖幅度短期内就可能超过1.5摄氏度。
A landmark report on climate change was released on Monday by the Intergovernmental Panel on Climate Change (IPCC), the United Nations body for assessing the science related to climate change.
The UN climate panel sounded a dire warning, saying the world is dangerously close to runaway warming – and that humans are "unequivocally" to blame.
Unless immediate, rapid and large-scale action is taken to reduce emissions, the report says, the average global temperature will likely cross the 1.5-degree Celsius warming threshold within the next 20 years.
这份3000多页的报告由234位气候科学家历时3年撰写而成，是IPCC自1988年成立以来发布的第6份报告的第一部分，其余部分将于2022年完成。
Describing the report as a "code red for humanity," UN Secretary-General António Guterres urged an immediate end to coal energy and other high-polluting fossil fuels. "Countries should also end all new fossil fuel exploration and production, and shift fossil fuel subsidies into renewable energy."
"The alarm bells are deafening," Guterres said in a statement. "This report must sound a death knell for coal and fossil fuels, before they destroy our planet."
IPCC 在报告中表示，无论温室气体的排放轨迹如何，到2030年左右，地球平均表面温度预计将比前工业化时期的水平高出1.5或1.6摄氏度。
报告还警告称，大气中的温室气体含量已经高到足以保证气候在几十年甚至几个世纪内受到破坏。除此之外，气候变化还会带来更多致命热浪、超级飓风和其他极端天气。
In its first major scientific assessment since 2014, the IPCC said that Earth's average surface temperature is projected to hit 1.5 or 1.6 degrees Celsius above preindustrial levels at around 2030, no matter what trajectory greenhouse gas emissions take in the meantime.
Already, greenhouse gas levels in the atmosphere are high enough to guarantee climate disruption for decades if not centuries, scientists warn in the report.
That's on top of the deadly heatwaves, powerful hurricanes and other weather extremes that are happening now and are likely to become more severe.
Drawing on more than 14,000 scientific studies, the report gives the most comprehensive and detailed picture yet of how climate change is altering the natural world – and what still could be ahead.
不可逆转的变化
IPCC的这份报告非常肯定地表示：“人类的影响使大气层、海洋和陆地变暖，这一点是明确无疑的。”
而由人类活动造成的排放已使今天的全球平均气温比前工业化时期的平均水平高出1.1摄氏度，如果不是由于大气污染的缓和效应，全球平均气温还会再高出0.5摄氏度。这意味着，随着社会逐步远离化石燃料，空气中的大部分气溶胶将消失，气温可能会飙升。
Emissions "unequivocally caused by human activities" have pushed today's average global temperature 1.1 Celsius higher than the preindustrial average – and would have pushed it 0.5 Celsius further if not for the tempering effect of pollution in the atmosphere, the report says.
That means that, as societies transition away from fossil fuels, much of the aerosols in the air would vanish – and temperatures could spike.
科学家警告称，气温若上升至比工业化前的平均水平高出1.5摄氏度以上，气候变化可能失控，带来灾难性的影响，比如酷热导致作物歉收，人们仅仅因为呆在户外就会死亡。
气温每升高0.5摄氏度，极端高温和暴雨以及一些地区干旱的强度和频率就会增加。目前，我们已经在见证升温1.1摄氏度带来的后果——今年，热浪在太平洋西北部造成数百人死亡，并打破了世界各地的记录；炎热和干旱引发的野火席卷了美国西部和西伯利亚森林，释放出创纪录的温室气体，也迫使希腊人乘船逃离家园。
想要阻止气候变化已经成为不可能，尽力减缓这一进程或许是我们最好的选择。
Scientists warn that warming more than 1.5 Celsius above the preindustrial average could trigger runaway climate change with catastrophic impacts, such as heat so intense that crops fail or people die just from being outdoors.
Every additional 0.5 Celsius of warming will also boost the intensity and frequency of heat extremes and heavy rainfall, as well as droughts in some regions.
Because temperatures fluctuate from year to year, scientists measure climate warming in terms of 20-year averages.
The 1.1 Celsius warming already recorded has been enough to unleash disastrous weather. This year, heatwaves killed hundreds in the Pacific Northwest and smashed records around the world. Wildfires fueled by heat and drought are sweeping away entire towns in the U.S. West, releasing record emissions from Siberian forests, and driving Greeks to flee their lands by ferry.
It's too late to prevent these particular changes. The best the world can do is to slow them down so that countries have more time to prepare and adapt.
"We are now committed to some aspects of climate change, some of which are irreversible for hundreds to thousands of years," said IPCC co-author Tamsin Edwards, a climate scientist at King's College London. "But the more we limit warming, the more we can avoid or slow down those changes."
“仍有选择”
但报告中也指出称，即使是减缓气候变化，留给我们的时间也不多了。
如果世界各国在未来十年大幅削减排放，平均气温在稳定之前仍可能在2040年上升1.5摄氏度，在2060年可能上升1.6摄氏度。而如果大幅减排没有实现，按目前的排放轨迹，到2060年地球可能会出现2.0摄氏度的升温，到本世纪末升温可能会达到2.7摄氏度。
上一次地球达到这个平均气温要回溯到300万年前了，彼时的海平面比现在要高出25米。
But even to slow climate change, the report says, the world is running out of time.
If the world drastically cuts emissions in the next decade, average temperatures could still rise 1.5 Celsius by 2040 and possibly 1.6 Celsius by 2060 before stabilizing.
If the world does not cut emissions dramatically and instead continues the current trajectory, the planet could see 2.0 Celsius warming by 2060 and 2.7 Celsius by the century's end.
The Earth has not been that warm since the Pliocene Epoch roughly 3 million years ago – when the first ancestors to humans were appearing and oceans were 25 meters higher than today.
如果气候变暖触发反馈循环，释放更多导致气候变暖的碳排放——比如北极永久冻土的融化或全球森林的枯死——情况可能会变得更糟。在这些高排放情景下，到2081-2100年，地球的温度将比工业化前的平均温度高出4.4摄氏度。
It could get even worse, if warming triggers feedback loops that release even more climate-warming carbon emissions – such as the melting of Arctic permafrost or the dieback of global forests. Under these high-emissions scenarios, Earth could broil at temperatures 4.4 Celsius above the preindustrial average by 2081-2100.
"We have already changed our planet, and some of those changes we will have to live with for centuries and millennia to come," said IPCC co-author Joeri Rogelj, a climate scientist at Imperial College London.
The question now, he said, is how many more irreversible changes we avoid: "We still have choices to make."
第26届联合国气候变化大会（COP26）将于今年11月在英国格拉斯哥召开。