一项新研究表明，为了控制气候变化，世界不但要削减二氧化碳排放，还要遏制一氧化二氮等不太为人所知的导致全球变暖的关键污染物。

过去数十年的全球气候讨论都集中在大气中含量最丰富的二氧化碳排放上。实现“净零”排放的共同目标通常仅指二氧化碳排放。

去年，100多个国家承诺到2030年将甲烷的排放量减少30%。甲烷是另一种碳基温室气体，比二氧化碳的吸热能力强得多。这些国家中的大多数还没有说明他们将如何在最后期限前完成任务。

与此同时，其他导致气候变暖的污染物，包括吸收辐射热量的黑碳，也被称为煤烟，以及制冷剂中发现的氢氟碳化合物和一氧化二氮，却很少受到关注。但根据周一发表在《美国国家科学院院刊》(Proceedings of the National Academy of Sciences)上的这项研究，这些污染物加上甲烷，造成了今天所见的一半全球变暖现象。

“当我们担心近况……我们需要看看其他非二氧化碳的气候影响因素，”该研究的合著者、华盛顿特区治理与可持续发展研究所所长德伍德·扎尔克(Durwood Zaelke)说。

这一点在各国通过减少化石燃料的使用来减少二氧化碳排放时尤为重要，化石燃料仍然被认为是全球变暖的主要原因。减少化石燃料使用将会减少空气污染，包括空气中的硫酸盐，其通过将太阳辐射反射到远离地球的地方来抵消一些气候变化。

科学家们说，这些硫酸盐掩盖了约0.5摄氏度的变暖，这意味着如果没有硫酸盐，积极的气候行动可能会导致温度暂时跳升——除非较少的污染物也得到解决。

研究发现，单是脱碳，到2045年就会使地球温度比工业化前高出2摄氏度。

相反，研究结果表明，如果同时控制所有气候污染物，世界可能最早在2030年就可以开始避免气候变暖，并在2030年至2050年期间将变暖速度减半。

没有参与这项研究的伦敦大学皇家霍洛威学院(Royal Holloway, University of London)气候科学家尤安·尼斯比特(Euan Nisbet)说，“这份具有里程碑意义的论文应该引发人们对全球目标的重大反思。”

原文：

Climate Action on CO2 Emissions Alone Won’t Prevent Extreme Warming

To control climate change, the world must go beyond cutting carbon dioxide emissions and curb lesser-known pollutants such as nitrous oxide playing a key role in warming the planet, new research suggests.

Decades of global climate discussions have focused on CO2 emissions, which are most abundant in the atmosphere. The common goal of reaching "net-zero" emissions refers most often to CO2 emissions alone.

Over the last year, more than 100 countries have pledged a 30% cut by 2030 to emissions from methane, another carbon-based greenhouse gas that is far more powerful at trapping heat than CO2. Most of those countries have yet to say how they will meet that deadline.

Meanwhile, scant attention has been paid to other warming pollutants, including black carbon, also called soot, which absorbs radiative heat, as well as hydrofluorocarbons found in refrigerants, and nitrous oxides. But together with methane, these pollutants are responsible for about half of the warming seen today, according to the study published on Monday in the journal Proceedings of the National Academy of Sciences.

"When we're worried about the near-term … we need to look at the other non-CO2 climate forcers," said study co-author Durwood Zaelke, president of the Institute for Governance & Sustainable Development in Washington DC.

This is especially important as countries pursue CO2 reductions through cutting back on their use of fossil fuels, still considered the main contributor to global warming. Using fewer fossil fuels will result in less air pollution, including airborne sulphates that actually counteract some climate change by reflecting solar radiation away from Earth.

Scientists say these sulphates are masking about 0.5 degree Celsius of warming that would be seen without them, meaning aggressive climate action could see temperatures temporarily jump higher – unless the lesser pollutants are tackled as well.

A path of decarbonization alone would see the planet breach 2 degrees Celsius of warming beyond pre-industrial temperatures by 2045, the study finds.

Conversely, reining in all climate pollutants together could see the world begin to avoid some warming as early as 2030 and halve the rate of warming between 2030 and 2050, the findings suggest.

"This landmark paper should bring about a major rethink" of global targets, said Euan Nisbet, a climate scientist at Royal Holloway, University of London, not involved in the study. "