气候变化是否即将无可挽回？

Climate change is reaching a tipping point
气候变化是否即将无可挽回？

Four years ago, it was Paris; for the next fortnight, it is Madrid. The scenery changes but the message does not: the world is running out of time to halt catastrophic climate change. The efforts made to honour the 2015 Paris pledge to limit the rise in global average temperature to under 2C, and ideally 1.5C, above the pre-industrial average, have been “utterly inadequate”, according to the UN secretary-general.

四年前是巴黎；接下来的两周是马德里。风景变了，但其中的讯息没有变：要停止灾难性的气候变化，留给世界的时间不多了。根据联合国(UN)秘书长安东尼奥•古特雷斯(António Guterres)的说法，为兑现2015年《巴黎协定》的承诺——将全球平均气温较工业化前平均水平的上升幅度限制在2摄氏度以下，最好是1.5摄氏度以下——所做的努力“完全不够”。

António Guterres, speaking in Spain ahead of the COP25 climate summit to negotiate an emissions trading system, warned that the Earth was belching its way towards a “point of no return”. He blamed politicians for continuing to subsidise fossil fuels and refusing to tax pollution.

古特雷斯在西班牙举行的《联合国气候变化框架公约》第25届缔约方会议前发表了演讲，该会议旨在建立一个碳排放交易市场。他警告说，地球的排放正走向“无可挽回的地步”。他指责政客们继续为化石燃料提供补贴，并拒绝对污染征税。

Perhaps Mr Guterres had caught sight of an article, published last week in the journal Nature, speculating whether the planet has already reached a critical state of warming and is now, climatically speaking, doomed. The analysis of nine climate “tipping points” concludes that we are in a “planetary emergency”, and possibly heading towards a hothouse Earth.

也许古特雷斯看到了上周发表在《自然》(Nature)期刊上的一篇文章。这篇文章猜测地球是否已经达到了变暖的临界状态，是否已经注定要变暖。文章对9个气候“临界点”进行分析并得出结论：我们正处于“行星紧急状态”，有可能正走向一个温室地球。

While some climate dangers, such as the runaway melting of ice sheets, have been historically predicted to happen if global average temperatures rise by 5C, later models have lowered some of those margins down to between 1C and 2C.

尽管历史上曾有人预测，如果全球平均气温上升5摄氏度，一些气候危险（如冰盖迅速融化）将会发生，但后来的一些模型将这种升温幅度下调至1摄氏度至2摄氏度之间。

Worse, the tipping points might interact with each other in unknown ways, the researchers warn, to threaten a global cascade of irreversible harm. “If damaging tipping cascades and a global tipping point cannot be ruled out, then this is an existential threat to civilisation,” writes Timothy Lenton, director of the Global Systems Institute at the University of Exeter, UK, who collaborated with academics in Germany and Denmark.

更糟糕的是，研究人员警告说，这些临界点可能以未知的方式相互作用，从而有可能造成一系列不可逆转的全球性危害。英国埃克塞特大学(University of Exeter)全球系统研究所(Global Systems Institute)主任蒂莫西•伦顿(Timothy Lenton)写道：“如果不能消除一系列破坏性的临界点和全球临界点，那么这是一个事关文明存亡的威胁。”他曾与德国和丹麦的学者合作过。

From a risk-management perspective, they urge immediate political and economic action to keep the rise to below 1.5C.

从风险管理的角度来看，他们敦促各国立即采取政治和经济行动，控制升温幅度在1.5摄氏度以下。

A tipping point is defined by the Intergovernmental Panel on Climate Change as a “large-scale discontinuity” in one piece of the Earth’s climate. Interrelated pieces include familiar totems such as Arctic sea ice and the Amazon rainforest. Less well-known components include the Atlantic Meridional Overturning Circulation, a “conveyor belt” that shifts warm water from the tropics northwards and brings deeper, colder water back south; and boreal forests, the evergreen thickets that ring northern latitudes, sometimes sit atop permafrost and act as a vast carbon store.

政府间气候变化专门委员会（Intergovernmental Panel on Climate Change，简称IPCC）将临界点定义为地球一部分气候的“大规模不连续性”。相互关联的组成部分包括一些熟悉的标志物，如北极海冰和亚马逊热带雨林。不太为人所知的组成部分包括大西洋经向翻转环流，这是一种“传送带”，将热带地区的温水向北转移，并将更深、更冷的水带回南方；还包括北方森林，这是环北纬地区的常绿灌木丛，有时位于永久冻土之上，充当巨大的碳储存库。