发现 | 二氧化碳去哪了？

二氧化碳的含量是否会继续上升取决于人类的行为。碳排放量目前处于历史上的高水平，在该速率下，空气中的二氧化碳含量必然会继续增长。若要稳定或降低二氧化碳水平，碳排放量必须进行削减。若空气中二氧化碳的含量持续上升的话，气候会继续变暖，海洋会持续酸化。

Where Is All That Carbon Dioxide Going?

11月13日，一队国际科学家在波恩气候谈判中宣布：今年人类温室气体排放量重新出现了增长，而在前三年，这个数字基本保持不变。根据他们的预测，2017年的排放量将会达到创纪录的410亿吨。同时，他们预测，化石燃料的燃烧也会增长2个百分点。

An international team of scientists announced today at the Bonn climate talks that human emissions of the greenhouse gas carbon dioxide are again rising this year, after three years of remaining basically flat. They project that emissions will reach a record 41 billion tons in 2017, alongside a projected 2 percent rise in burning of fossil fuels.

然而，空气中的碳含量并与排放量相当；海洋和大地都可以吸收并释放大量的二氧化碳，且由于气候循环及其他因素，这种平衡每年都有所不同。科学家们仅能估算这个数字。在2015及2016年，尽管碳排放量很稳定，大气中二氧化碳含量实际上增长了创纪录的3/1, 000, 000（百万分之三）。今年，这一数字还在继续增长，或许会增长到405.5/1, 000, 000 （百万分之四百零五点五）。

However, the carbon level in the air does not exactly parallel emissions; the ocean and land both absorb and give off large quantities of CO2, and the balance can vary year to year due to natural climate cycles and other factors. Scientists can only approximate the numbers. Atmospheric carbon dioxide actually went up at record annual rates of about 3 parts per million in 2015 and 2016, even though emissions were steady during those years. Levels continue to ascend this year, and will probably reach a record average of 405.5 parts per million.

Concurrent with the release of this year’s emissions figures, Galen McKinley, a professor of earth and environmental sciences at Columbia University and its Lamont Doherty Earth Observatory, coauthored a paper published today in the journal Nature Climate Change, in which she and colleagues discuss the difficulties of tracking the sources and destinations of carbon dioxide. Below, she explains.

我们的二氧化碳去哪里了？

Where do our carbon dioxide emissions go?

人类排放的二氧化碳只有50%会存留在大气中。剩下的部分大体上一半被陆地生物圈吸收，一半被海洋吸收。大气中的二氧化碳具有平衡二氧化碳排放和陆地、海洋对其吸收的功能。二氧化碳的排放和陆地、海洋对其吸收都可根据时间变化。

Only about 50 percent of the CO2 from human emissions remains in the atmosphere. The remainder is approximately equally split between uptake into the land biosphere and into the ocean. The CO2 in the atmosphere is a function of the balance between emission and uptake into the land and ocean. Both emissions and the uptake by the land and ocean can vary over time.

我们最了解该系统的哪一部分？最不了解哪一部分？

Which parts of the system do we best, and least, understand?

我们得出的自工业时代起海洋所吸收的碳总量，存在10%以内的误差。根据时间变化的吸收量存在更大的不确定性。也许一年吸收量多了一点，接下来的一年又少了一点。详细的空间分解也存在不确定性，尤其是范围变小了之后。比如，我们知道北大西洋这个区域吸收了大量的碳，但是根据纬度和精度确定具体位置的吸收量便更加困难。到目前为止，全球碳预算 告通过碳排放量与大气中剩余或进入海洋的碳含量之差来估算陆地的碳吸收量。但是我们在不断进步。根据我们在长期的实地研究地点以及特定的现场活动中进行的观察和预算，我们已经建立了相应的模型。现在，这些模型已首次用于直接估算陆地吸收量。当然，这其中还存在着许多不确定性。

The cumulative ocean uptake of all the carbon we have emitted over the industrial age has been quantified to within about a 10 percent error. Uncertainties are larger for the variability in the uptake over time. So, perhaps one year has a bit more uptake, the next a bit less. The detailed spatial breakdown also has uncertainties, particularly as the scales get smaller. For example, we know that the North Atlantic is a region of very intense carbon uptake, but the uptake at any latitude and longitude is harder to nail down. On land, there is much knowledge about the processes driving uptake and release of carbon. But land varies widely from place to place, so scaling up our understanding from field sites is a major challenge. Until now, the global budget has estimated the land uptake as a difference between what is emitted and what remains in the atmosphere or goes into the ocean. But we’re making progress. Models have been developed based on observations and budgets at long-term field sites and in dedicated field campaigns. Now, these models are being used to directly estimate the land uptake for the first time. Of course, there are many uncertainties remaining.

在秘鲁亚马逊，一位研究者正在研究一场农民用于清除树木所放的火。

In the Peruvian Amazon, a researcher studies a fire set by farmers in order to clear land.

(Kevin Krajick/Earth Institute)

2015年至2016年发生的哪些事情导致了大气中二氧化碳含量如此迅速的增长？

What happened in 2015-2016 to drive such sharp increases in atmospheric CO2?

在大型厄尔尼诺现象的发生的年度，比如2015年至2016年，陆地生物圈作为一个整体，吸收了更少的碳。这是因为厄尔尼诺使得许多地方面临干旱和升温。这导致了部分地区的火灾，以及部分地区植被量的减少。海洋存留了相对多的碳。但（碳）净差额（的增长更多来自于）大气中二氧化碳的增长。1997年至1998年较强厄尔尼诺现象发生时，我们也发现了相似的变化。

In a year with a large El Ni?o such as 2015-16, the land biosphere, as a whole, took up less carbon. This was because the El Ni?o caused a lot of places to dry out and warm up. This caused fires in some places, and less plant growth in others. The ocean retained a bit more carbon. But the net balance was a larger growth rate of atmospheric CO2. Similar changes were observed with the strong 1997-98 El Ni?o.

根据巴黎气候协议，国家应该上 他们的排放量，科学家应证实这方面的信息。证实信息的可靠性如何？

Under the Paris climate accord, nations are supposed to report their emissions, and scientists try to verify the information. How reliable is the verification effort?

现在，全球碳预算不足以准确地验证国家的排放估量。首先，由于许多国家都参与其中，一些国家多出的部分可以抵消一些国家不足的部分。并且，陆地及海洋碳吸收量具有巨大的不确定性。验证碳排放减少的整体效用是一项长期的科学目标。我们正努力追踪区域性、国家区域内的碳排放。我们的努力获得了很大的进展，但仍十分基础。现在的方法主要结合了现场数据、卫星数据以及大气传输模型。若要形成一个真正的验证体系，实时观测能力需迅猛发展，模型也需改良。

At present, the global carbon budget is not sufficiently precise to verify national emission estimates. First, because there are so many nations, and a bit more from one can easily balance out a bit less from another. And, because of the substantial uncertainties in the uptake by land and oceans. It is a long-term scientific goal to verify at least the integrated impact of emission reductions. Efforts are underway to track emissions regionally, down to the national level. These efforts have made great strides in recent years, but are still rudimentary. The current methods use field data, satellite data, and atmospheric transport models, all combined. To come up with a real verification system will require an explosion of real-time observational capacity, as well as improved models.

你认为二氧化碳在空气中的含量会不断增加吗？如果会，这意味这什么呢？

Do you think CO2 in the air will keep going up? If so, what are the implications?

二氧化碳的含量是否会继续上升取决于人类的行为。碳排放量目前处于历史上的高水平，在该速率下，空气中的二氧化碳含量必然会继续增长。若要稳定或降低二氧化碳水平，碳排放量必须进行削减。若空气中二氧化碳的含量持续上升的话，气候会继续变暖，海洋会持续酸化。

Whether or not CO2 levels will continue to rise depends on human actions. Emissions are currently at historically high levels, and at this rate the CO2 in the atmosphere will certainly continue to rise. Emissions have to be cut drastically for atmospheric CO2 levels to stabilize or decline. Warming climate and acidification of the ocean will continue as long as atmospheric CO2 continues to go up.

会出现突然改变碳平衡以及未来展望的惊喜吗？

Could there be surprises that would suddenly change the carbon balance, and prospects for the future?

在大洋中，我们认为海洋环流可以影响海洋的碳吸收量。以往的证据可以证明这些变化。同时，人们认为大洋只有有限的能力，但是是复杂且依靠时间的。以一万年的时间维度计算，海洋可以吸收至少85%的碳排放。海洋每一千年可完全混合且需要数次混合来吸收所有的碳。但是由于碳在海水中可溶性很强，从某种意义上来讲，海洋的能力是无限的。若只考虑较长的时间范围，海洋将吸收碳。但是人类社会更倾向于考虑更短的时间周期。在这种情况下，减缓洋流确实可以影响大气中二氧化碳的含量。现今的陆地生物圈的二氧化碳累积吸收量基本为零。我所指的累积量，指的是前工业化时代以来土地使用所带来的二氧化碳排放以及森林重新增长所吸收的二氧化碳，以及由于大气中二氧化碳含量的升高带来的增长。

In the ocean, we believe that ocean circulation changes could impact ocean carbon uptake. There is evidence for such changes in the past. There is also a notion that the ocean has only so much total capacity, but this is complex and time dependent. On time scales of 10,000 years, the ocean should be able to absorb at least 85 percent of all emissions. The ocean mixes fully only once every 1,000 years, and it needs multiple mixes to sop up all the carbon. But since carbon is very soluble in seawater, in some sense the ocean capacity is infinite. If you care only about very long time scales, the carbon will be taken up by the oceans. But human society tends to care about much shorter time scales. For these, slowing ocean circulation certainly could impact the atmospheric CO2 load. On land to date, the cumulative carbon uptake of the biosphere is approximately zero. What I mean by cumulative is the integrated sum of all carbon emissions due to land use change since the preindustrial era, and carbon uptake occurring with forest regrowth and enhanced growth due to more CO2 in the atmosphere.

目前，这种累积效应似乎没有净吸收。同时我们知道，气候变暖会让土壤和冻土层的二氧化碳释放出来；一些森林受到气候变暖影响，更容易遭受干旱和火灾。此外，我们需要农业来养活人类。因此，我认为陆地上并没有人们可以希求的长期自然地储存大量碳的储藏池。人类采取的行动，如农业上的保护措施，能够适当地提升存储能力，减少流失。但是相比于海洋的容量，陆地储存总量大概少了成百上千年。然而，在短期时间范围内，陆地会产生巨大的影响。2015-2016年的厄尔尼诺现象就清楚地体现了这一点。

Right now, this cumulative effect seems to be no net uptake. At the same time, we know that climate warming will release at least some CO2 from soils and permafrost, and some forests are more vulnerable to drought and fire with warming. And. we need agriculture to feed people. So, there does not seem to me to be a large reservoir on land where one can expect lots of carbon to be naturally stored for the long term. Human actions could enhance some storage and reduce losses, for example with conservation practices in agriculture. But compared to the capacity in the ocean, likely accumulations will be small for hundreds to thousands of years. Nonetheless, on shorter timescales, the land can have a huge impact. The 2015-16 El Ni?o illustrates this clearly.

The translation is for your reference only.

译 仅供参考，内容以英 为准

编译：忆念、南心