上周，联合国发布了一份《气候问题评估报告》，供各国政府参考。国内媒体没怎么报道这件事，但在国际上，它都是各国的头版新闻。一般来说，政府单位的报告都写得四平八稳、滴水不漏。但是，这份报告是罕见的例外，它写得非常明确尖锐，结论就是四个字：“大难临头”。

报告认为，根据各种科学研究和观测结果，可以认定：气候灾难已经发生了，并将继续加剧。 报告描绘了非常可怕的全球变暖进程，地球的平均气温，目前比工业革命前上升了1.2度，估计未来一两年内就会上升1.5度。如果温室气体排放量继续增加，2050年前将会上升2度，本世纪末之前达到3度。人类现在所做的种种减碳努力，并不能避免灾难，只是为了不让最糟糕的结果发生。

我们会遭遇什么样的灾难？联合国报告是这样描述的：

“地球将变得干燥许多，整个生态系统被破坏，导致大规模物种灭绝，并使全球的粮食保障面临巨大风险。

以下五种灾难现象将会越来越严重：（1）高温，（2）干旱，（3）洪水，（4）飓风，（5）海平面上升。”

气候灾难其实已经发生了，比如上个月郑州”千年一遇”的大暴雨，再比如这个月，欧洲遭遇史上最热的夏天。就在几天前，意大利报告欧洲有记录以来最高温 48.8 摄氏度，同一时间西班牙是47.2度，希腊是46度。气候灾难不再是一个科学名词，而是日常生活中，真真实实发生在每个人身边。

-阮一峰《科技爱好者周刊（第 172 期）：我们会死于气候灾难吗？》

以下为联合国2021年气候问题总结报告的摘要，摘录、翻译自文献[1]，详细信息见 AR6 Climate Change 2021: The Physical Science Basis

Headline Statements from the Summary for Policymakers

A. The Current State of the Climate 当前的气候状况

A.1 It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.

A.1 人类的影响已经确确实实地使得地球大气、海洋和陆地变暖。大气、海洋、冰冻圈和生物圈已经发生了广泛而迅速的变化。

A.2 The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.

A.2 整个气候系统最近发生变化的规模、以及气候系统许多方面的现状是几百上千年来前所未有的。

A.3 Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report (AR5).

A.3 在全球的每一个区域，人类导致的气候变化已经影响了众多极端天气和气候。自上一次评估（第五次评估报告）以来，观测到的极端气候变化——比如热浪、强降水、干旱和热带气旋，尤其是它们对人类的负面影响——变得更加强烈。

B. Possible Climate Futures 可能的气候特征

B.1 Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.

B.1 考虑到所有的排放情况，全球表面温度将会一直升温，最早至本世纪中叶结束。除非在未来几十年内大幅减少二氧化碳和其他温室气体排放，否则在21世纪全球变暖将会超过1.5°C和2°C这两个指标。

B.2 Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.

B.2 逐渐严重的气候变暖将会直接加剧气候系统的许多变化。这些变化包括极端高温气候、海洋热浪、强降水、部分地区农业和生态干旱、强热带气旋比例增加，以及北极海冰、积雪覆盖和冻土的减少。

B.3 Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.

B.3 持续的全球变暖预计会进一步恶化全球水循环，包括全球水循环的可变性、全球季风降水，和由旱汛期导致的各种事件的严重程度。

B.4 Under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere.

B.4 随着二氧化碳排放的增加，海洋碳沉积和陆地碳沉积会越来越无力减缓二氧化碳在大气层的堆积。

B.5 Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.

B.5 许多由于过去和将来的温室气体排放而导致的变化，尤其是在海洋、冰盖和全球海平面的变化，将会在未来几百上千年无法逆转。

C. Climate Information for Risk Assessment and Regional Adaptation 用于风险评估和区域适应的气候信息

C.1 Natural drivers and internal variability will modulate human-caused changes, especially at regional scales and in the near term, with little effect on centennial global warming. These modulations are important to consider in planning for the full range of possible changes.

C.1 自然因素和气候系统内部的多变性会调节这些人为导致的气候变化，这种调节在区域间和近期内尤为明显。然而，从百年的时间跨度来看，这些调节对全球变暖影响甚微。在政府机构规划各种可能的变化时，必须考虑这些调节情况。

C.3 Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and warming substantially larger than the assessed very likely range of future warming cannot be ruled out and are part of risk assessment.

C.3 由气候变化导致的低概率事件，例如冰盖崩塌、海洋环流突变、复合极端事件、以及大大高于预期范围的气候变暖，都不容忽视，并且应该作为风险评估的一部分。

D. Limiting Future Climate Change 限制未来气候变化

D.1 From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in CH4 emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.

D.1 从物理科学的角度来看，要想把由人类引起的全球变暖限制在特定水平，就需要限制二氧化碳排放量，使得二氧化碳净排放量至少为零，与此同时大幅减少其他温室气体排放。有效、快速和持续地减少甲烷排放量能够减少气溶胶污染，从而限制由气溶胶污染所造成的变暖效应，同时也能够改善空气质量。

D.2 Scenarios with low or very low greenhouse gas (GHG) emissions (SSP1-1.9 and SSP1- 2.6) lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios (SSP3-7.0 or SSP5-8.5). Under these contrasting scenarios, discernible differences in trends of global surface temperature would begin to emerge from natural variability within around 20 years, and over longer time periods for many other climatic impact-drivers (high confidence).

D.2 相对于过量的温室气体排放（SSP3-7.0 或 SSP5-8.5），维持温室气体排放量在低或非常低（SSP1-1.9 和 SSP1-2.6）的水平，就可以在几年内对温室气体、气溶胶浓度以及空气质量产生明显影响。

参考文献

[1] IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson- Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press.

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