按：自然(Nature)2024年3月发表了题为“Climate models can’t explain 2023’s huge heat anomaly – we could be in uncharted territory”文章，作者是美国国家航空航天局戈达德空间研究所所长Schmidt G先生。此文很有价值，特此记录于此。

Schmidt G, Climate models can’t explain 2023’s huge heat anomaly – we could be in uncharted territory, Nature, 2024. 627(8004): 467-467.

NATURE：气候模型无法解释2023年重大热异常——我们可能正处于未知领域

Gavin Schmidt

When I took over as the director of NASA’s Goddard Institute for Space Studies, I inherited a project that tracks temperature changes since 1880. Using this trove of data, I’ve made climate predictions at the start of every year since 2016. It’s humbling, and a bit worrying, to admit that no year has confounded climate scientists’ predictive capabilities more than 2023 has.

当我接任美国国家航空航天局戈达德空间研究所所长时，我继承了一个追踪1880年以来温度变化的项目。利用这些数据宝库，自2016年以来，我每年年初都会进行气候预测。承认没有一年比2023年更让气候科学家的预测能力感到困惑，这让人感到羞愧，也有点担心。

For the past nine months, mean land and sea surface temperatures have overshot previous records each month by up to 0.2 °C - a huge margin at the planetary scale. A general warming trend is expected because of rising greenhouse-gas emissions, but this sudden heat spike greatly exceeds predictions made by statistical climate models that rely on past observations. Many reasons for this discrepancy have been proposed but, as yet, no combination of them has been able to reconcile our theories with what has happened.

在过去的九个月里，陆地和海面的平均温度每月都比以前的记录高出0.2°C，这在全球尺度上是一个巨大的增幅。由于温室气体排放量的增加，预计会出现普遍的变暖趋势，但这一突然的高温峰值大大超过了基于过去观测的统计气候模型的预测。造成这种差异的许多原因已经被提出，但到目前为止，还没有将它们结合起来，使我们的理论与所发生的情况相一致。

For a start, prevalent global climate conditions one year ago would have suggested that a spell of record-setting warmth was unlikely. Early last year, the tropical Pacific Ocean was coming out of a three-year period of La Niña, a climate phenomenon associated with the relative cooling of the central and eastern Pacific Ocean. Drawing on precedents when similar conditions prevailed at the beginning of a year, several climate scientists, including me, put the odds of 2023 turning out to be a record warm year at just one in five.

首先，一年前普遍的全球气候状况表明，不太可能出现创纪录的温暖期。去年年初，热带太平洋刚刚结束为期三年的拉尼娜现象，这是一种与太平洋中部和东部相对偏低有关的气候现象。根据年初类似情况普遍存在的先例，包括我在内的几位气候科学家认为，2023年扭转成创纪录温暖年份的几率仅为五分之一。

El Niño — the inverse of La Niña — causes the eastern tropical Pacific Ocean to warm up. This weather pattern set in only in the second half of the year, and the current spell is milder than similar events in 1997–98 and 2015–16.

厄尔尼诺现象—与拉尼娜现象相反—导致东部热带太平洋变暖。这种天气形态只在去年下半年出现，目前的天气比1997-98年和2015-16年的类似事件要温和。

However, starting last March, sea surface temperatures in the North Atlantic Ocean began to shoot up. By June, the extent of sea ice around Antarctica was by far the lowest on record. Compared with the average ice cover between 1981 and 2010, a patch of sea ice roughly the size of Alaska was missing. The observed temperature anomaly has not only been much larger than expected, but also started showing up several months before the onset of El Niño.

然而，从去年3月开始，北大西洋的海面温度开始飙升。到6月，南极洲周围的海冰范围是迄今为止有记录以来最低的。与1981年至2010年的平均冰盖相比，大约相当于阿拉斯加大小的一块海冰消失了。观测到的温度异常不仅比预期的要大得多，而且在厄尔尼诺现象爆发前几个月就开始出现。

So, what might have caused this heat spike? Atmospheric greenhouse-gas levels have continued to rise, but the extra load since 2022 can account for further warming of only about 0.02 °C. Other theories put forward by climate scientists include fallout from the January 2022 Hunga Tonga - Hunga Ha‘apai volcanic eruption in Tonga, which had both cooling effects from aerosols and warming ones from stratospheric water vapour, and the ramping up of solar activity in the run-up to a predicted solar maximum. But these factors explain, at most, a few hundredths of a degree in warming (Schoeberl, M. R. et al. Geophys. Res. Lett. 50, e2023GL104634; 2023). Even after taking all plausible explanations into account, the divergence between expected and observed annual mean temperatures in 2023 remains about 0.2 °C - roughly the gap between the previous and current annual record.

那么，是什么原因导致了这种热峰值？大气温室气体水平持续上升，但自2022年以来的额外负荷只能解释进一步变暖约0.02°C的原因。气候科学家提出的其他理论包括2022年1月汤加Hunga Tonga-Hunga Ha’apai火山喷发的沉降物，该火山喷发既有气溶胶的冷却作用，也有平流层水蒸气的变暖作用，以及在预测的太阳活动高峰之前太阳活动的增加。但这些因素最多只能解释百分之几度的变暖（Schoebel，M.R.等人，Geophys.Res.Lett.50，e2023GL104634；2023）。即使考虑到所有合理的解释，2023年的预期年平均气温和观测年平均气温之间的差异仍约为0.2°C，大致相当于先前与现在的年记录之间的差距。

There is one more factor that could be playing a part. In 2020, new regulations required the shipping industry to use cleaner fuels that reduce sulfur emissions. Sulfur compounds in the atmosphere are reflective and influence several properties of clouds, thereby having an overall cooling effect. Preliminary estimates of the impact of these rules show a negligible effect on global mean temperatures — a change of only a few hundredths of a degree. But reliable assessments of aerosol emissions rely on networks of mostly volunteer-driven efforts, and it could be a year or more before the full data from 2023 are available.

还有一个因素可能在起作用。2020年，一些新规则要求航运业使用更清洁的燃料，以减少硫排放。大气中的硫化合物具有反射性，并影响云的某些特性，从而具有整体冷却效果。对这些规则影响的初步估计表明，对全球平均气温的影响可以忽略不计——只有百分之几度的变化。但气溶胶排放的可靠评估依赖于主要由志愿者推动的网络，可能需要一年或更长时间才能获得2023年的完整数据。

This is too long a wait. Better, more nimble data-collection systems are clearly needed. NASA’s PACE mission, which launched in February, is a step in the right direction. In a few months, the satellite should start providing a global assessment of the composition of various aerosol particles in the atmosphere. The data will be invaluable for reducing the substantial aerosol-related uncertainty in climate models. Hindcasts, informed by new data, could also provide insights into last year’s climate events.

这种等待太长了。显然需要更好、更灵活的数据收集系统。美国国家航空航天局的PACE发射任务于2月发射，是朝着正确方向迈出的一步。几个月后，该卫星将开始对大气中各种气溶胶颗粒的成分进行全球评估。这些数据对于减少气候模型中与气溶胶相关的大量不确定性将是非常宝贵的。根据新数据，通过反演还可以提供针对上年度气候事件的见解。

But it seems unlikely that aerosol effects provide anything close to a full answer. In general, the 2023 temperature anomaly has come out of the blue, revealing an unprecedented knowledge gap perhaps for the first time since about 40 years ago, when satellite data began offering modellers an unparalleled, real-time view of Earth’s climate system. If the anomaly does not stabilize by August — a reasonable expectation based on previous El Niño events — then the world will be in uncharted territory. It could imply that a warming planet is already fundamentally altering how the climate system operates, much sooner than scientists had anticipated. It could also mean that statistical inferences based on past events are less reliable than we thought, adding more uncertainty to seasonal predictions of droughts and rainfall patterns.

但气溶胶效应似乎不太可能提供任何接近完整答案的东西。总的来说，2023年的温度异常突然出现，揭示了前所未有的知识差距，这可能是自大约40年前以来的第一次，当时卫星数据开始为建模者提供无与伦比的地球气候系统实时视图。如果异常现象在8月前不能稳定下来—这是基于之前厄尔尼诺事件的合理预期—那么世界将处于未知领域。这可能意味着，地球变暖已经从根本上改变了气候系统的运行方式，比科学家预期的要快得多。这也可能意味着，基于过去事件的统计推断不如我们想象的那么可靠，给干旱和降雨模式的季节性预测增加了更多的不确定性。

Much of the world’s climate is driven by intricate, long-distance links — known as teleconnections — fuelled by sea and atmospheric currents. If their behaviour is in flux or markedly diverging from previous observations, we need to know about such changes in real time. We need answers for why 2023 turned out to be the warmest year in possibly the past 100,000 years. And we need them quickly.

世界气候的大部分是由复杂的远距离联系驱动的，这种联系被称为遥相关，由洋流和大气流推动。如果它们的行为与之前的观察结果不一致或明显不同，我们需要实时了解这些变化。我们需要答案来解释为什么2023年可能是过去10万年中最热的一年。我们很快就需要它们。