Explainer: How Does Climate Change Affect the Ocean?
解读：气候变化如何影响海洋？
The ocean has cushioned the blow of global heating, but at a cost to the stability of climate systems and marine life
海洋充当了全球变暖的缓冲器，但代价则是气候系统和海洋生态的稳定性。
As climate change tightens its grip, the effects are being felt across the planet. The global ocean plays a key role and has so far soaked up most of the carbon dioxide and excess heat human activities have produced. But it is also vulnerable. Already some significant changes are underway, and the climate disruption to our seas looks set to worsen.
随着气候变化的影响日益加剧，全球都受到了影响。海洋发挥的作用十分关键，迄今为止吸收了人类活动产生的大部分二氧化碳和过剩的热量。但海洋也很脆弱。海洋如今正经历着一些重大的变化，气候变化对海洋的破坏似乎将进一步恶化。
1. Rising temperatures
1. 温度上升
About 90% of the excess heat trapped by atmospheric greenhouse gases is eventually soaked up by the world’s oceans. Because oceans are so big, the temperature change to the seawater can seem small – the sea surface layer has warmed by just over 0.5℃ in the last century. That’s still enough to cause significant disruption, and the warming is accelerating.
大气中的温室气体所蓄积的热量，其中约90%最终被海洋吸收。与海洋庞大的体量相比，海水温度的变化显得似乎微不足道——过去100年间，海洋表层温度只升高了0.5摄氏度。但即便是这0.5摄氏度也足以造成重大破坏，而且海洋变暖正在加速。
Things expand as they warm, becoming less dense and taking up more space. The oceans are no different. Indeed, between 1993-2010, thermal expansion is thought to have raised sea levels by an average of 1.1 millimetres a year, accounting for much of the overall rise we have seen.
物质遇热膨胀，密度降低，体积变大，海洋也不例外。事实上人们认为1993至2010年间热膨胀导致海平面每年平均上升1.1毫米。在我们所看到的海平面上升中，热膨胀导致的占很大一部分。
Warmer water also influences the atmosphere above it. Increased sea surface temperatures are associated with making hurricanes and tropical cyclones more powerful, potentially increasing the number of the most severe category 4 or 5 storms that strike islands and coastal areas. Warmer water can also dissolve less carbon dioxide, which means more will stay in the atmosphere to accelerate global warming.
海水变暖也会影响其上方的大气。海面温度升高会增大飓风和热带气旋的威力，可能导致岛屿和沿海地区遭遇更多的台风和强台风。海水温度越高，溶解的二氧化碳量就越少，这就意味着会有更多的二氧化碳留在大气中，加速全球变暖。
Just like on land, rising temperatures in the oceans generate damaging heatwaves. They occur when unusual weather conditions or water currents cause above-average water temperatures for at least five consecutive days. But they can last for months or even years. A marine heatwave called “The Blob” hung around the northern Pacific from 2013-2015 and killed a million seabirds on the west coast of the United States.
和陆地一样，海洋温度上升也会产生破坏性的热浪。如果一个地区由于天气条件或水流的异常而连续五天出现海水异常温暖的情况，就意味着出现了海洋热浪。这一情况可以持续数月甚至数年。2013至2015年一场名为水泡（The Blob）的海洋热浪在北太平洋附近活动，造成美国西海岸100万只海鸟死亡。
2. Acidification
2. 酸化
As carbon dioxide dissolves in seawater, it reacts to form carbonic acid: a fairly weak acid, but enough to alter the pH of seawater, which is naturally alkaline. Since the industrial revolution, dissolved carbon dioxide is estimated to have lowered the average pH of the top layer of the oceans by 0.1 pH units, from about 8.2 to 8.1 (7 is neutral).
二氧化碳溶解在海水中会反应形成碳酸：虽然这是一种弱酸，但足以改变海水天然弱碱性的ph值。据估计，工业革命以来海水中溶解的二氧化碳已导致海洋表层的平均酸碱度降低了0.1，从8.2左右降至8.1（7为中性）。
That change doesn’t sound much, but because pH is measured on a logarithmic scale, it actually represents a nearly 30% increase in acidity. This has some significant knock-on effects for seawater chemistry and the ecosystems that rely on it.
这一变化听起来不大，但酸碱值是对数尺度的，0.1个单位实际表示酸度增加了近30%。这对海水的化学组成以及依靠海水的生态系统产生了一些显著的连锁反应。
The increase in acidity is particularly bad news for shellfish and other forms of sea life that use the mineral calcium carbonate to form their shells and exoskeletons. More acidic water can hold less of this mineral, so there’s less available for so-called calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals and calcareous plankton. Worse, the change in chemistry encourages existing carbonate structures to dissolve.
对于贝类以及其他利用矿物碳酸钙来形成外壳和外骨骼的海洋生物而言，酸度增加是个非常糟糕的消息。海水酸度越高，海水中的碳酸钙浓度就越低，可供牡蛎、蛤、海胆、浅水珊瑚、深海珊瑚和钙质浮游生物等钙化生物使用的量就越少。更糟糕的是，海水化学组分的变化加速了现有碳酸盐结构的溶解。
Coral is particularly vulnerable. Experiments on a small patch of Australia’s Great Barrier Reef show that artificially reducing the seawater carbon dioxide level, so restoring pH to pre-industrial levels, boosted coral calcification by 7%. Then, when the scientists raised the amount of carbon dioxide and so decreased ocean pH to the level expected by the end of this century, calcification dropped by a third.
珊瑚尤其脆弱。对澳大利亚大堡礁一小部分珊瑚的实验表明，人为降低海水中的二氧化碳含量从而将海水酸碱度恢复到工业化前的水平，促使珊瑚钙化率提高了7%。随后科学家提高二氧化碳含量，将海水酸碱度降至本世纪末的预计水平，钙化减少了三分之一。
3. Melting ice
3. 冰层融化
As climate change continues, many scientists believe it is inevitable that massive ice sheets in Greenland and Antarctica will collapse and melt entirely, eventually pouring enough water into the oceans to raise global sea levels by several metres. It will take time – hundreds, perhaps thousands of years – but the melting is accelerating. The UN’s climate body now projects that, under a low-emissions scenario, average sea level will rise between 61cm and 1.1m by the end of the century.
许多科学家认为，随着气候变化继续发展，格陵兰岛和南极的大量冰盖必将彻底崩塌、融化，最终进入海洋，导致全球海平面上升数米。这需要时间，也许是几百年、几千年，但融化正在加速。根据联合国气候机构目前的预测，低排放情况下，到本世纪末海平面将平均上升61至110厘米。
By 2050, rising seas could push peak high tides above land currently home to at least 300 million people, mostly in Asia.
到2050年，海平面上升可能导致至少3亿人的家园被海水淹没，其中大部分地区位于亚洲。
Coastal ecosystems will be affected too. Beach and dune environments face more severe and frequent flooding and erosion, while sensitive freshwater habitats including mudflats and marshes – needed for bird species to breed – will be swamped with seawater.
沿海生态系统也会受到影响。海滩和沙丘环境面临更严重、更频繁的浸泡和侵蚀，泥滩、沼泽等供鸟类繁殖的敏感的淡水栖息地则将被海水淹没。
Sea ice, which forms when seawater freezes each polar winter, is also melting and thinning more and more each summer. Melting of this ice doesn’t significantly contribute to sea levels, but it does pose big problems for creatures that rely on it for their habitat. Most notably, polar bears need sea ice to hunt seals, and studies show many of the 25,000 bears estimated to remain in the Arctic are struggling. One colony of animals around the Southern Beaufort Sea, in northeastern Alaska and Canada, was found to have declined by 40% between 2001 and 2010.
极地冬天海水结成的海冰也会在夏天一年年地逐渐融化变薄，导致海冰整体覆盖和范围不断缩小。海冰融化对海平面上升没有显著影响，但却给以海冰为栖息地的生物带来了大问题。值得注意的是，北极熊需要借助海冰来捕猎海豹。研究表明，北极地区剩余约2.5万头北极熊中，大部分都在挣扎求生。研究发现，2001至2010年间阿拉斯加和加拿大东北部南波弗特海附近一个北极熊种群的数量下降了40%。
4. Changes in ocean currents
4. 洋流变化
Ocean currents are vulnerable to the effects of climate change. At present, those currents act as massive global conveyor belts: as winds push through the atmosphere from the warm equator to the colder poles, they drag surface water with them. Cooled by the chilly polar air, this water becomes denser, and so sinks to the deep ocean, where it is pushed back towards the equator (becoming warmer, less dense and rising as it goes) by the next batch of denser water coming from above. Round and round the cycles go, transporting and mixing nutrients as they swirl along.
洋流易受气候变化的影响。目前这些洋流就是大型的全球传送带：气流从温暖的赤道吹向寒冷的两极时会带着表层海水一起流动。海水被寒冷的极地空气冷却后，密度增加，沉入深海，然后又被从表层新沉降下来的密度更大的水推回赤道（并在这一过程中变暖、密度降低、上升），如此周而复始，并同时运输和混合营养物质。
Melting ice interferes with this system. Huge amounts of fresh water pouring in at the poles lowers the density of the seawater, making it slower to sink. Without the same driving downward force, the whole global cycle can weaken. In 2018, scientists suggested that the major current in the Atlantic Ocean had slowed by about 15%. And some studies predict that could worsen to more than 30% by 2100.
冰层融化会干扰这一系统，大量淡水涌入两极导致海水密度降低，下沉速度变慢。如果没有同样的下行推动力，整个全球大循环可能会减弱。2018年，科学家认为大西洋主要洋流的速度已经降低了约15%。一些研究预测到2100年情况可能进一步恶化，减速可能达到30%以上。
Based on what has happened in the past, scientists say slower ocean currents can bring significant changes in the Earth’s atmosphere, and so to the weather. Winters in Europe could be much colder (an idea taken to extremes in the film The Day After Tomorrow). Meanwhile, the waters of the South Atlantic could become warmer, and because sea surface temperature influences wind and rainfall, this could disrupt monsoon cycles that are vital for crops across Asia and South America.
根据以往的情况，科学家称洋流变慢可能导致地球大气发生重大变化，进而影响天气。欧洲的冬天可能会更冷（电影《后天》所讲述的正是这种极端状况）。与此同时，南大西洋的海水可能会变暖，由于海面温度影响风和降雨，因而可能会破坏对亚洲和南美农作物至关重要的季风周期。
5. Deoxygenation
5. 缺氧
Ocean creatures rely on oxygen dissolved in seawater, just as we breathe it from the atmosphere. But climate change is gradually draining oxygen from the seas: about 1-2% is thought to have been lost from 1960 to 2010, and that could rise to 4% by 2100.
和我们在大气中呼吸氧气一样，海洋生物依靠溶解在海水中的氧生存。但气候变化正导致海洋中的氧气逐渐流失：1960至2010年间约1%到2%的氧已经流失，到2100年这一数字可能上升至4%。
There are several reasons. Warmer water can hold less of the gas, while disruption to ocean currents limits the amount of oxygen transported from the surface to the depths.
导致氧流失的原因有几个。海水温度上升导致气体的溶解率下降，洋流遭到破坏则限制了氧气从海洋表面向深海的输送。
A growing problem occurs when the fertiliser and other nutrients added to agricultural soils drain into rivers and eventually get dumped into coastal waters. Boosted by the unexpected supply of food, algae can grow and proliferate rapidly to form massive floating blooms – sometimes called green (or red) tides. These can be problematic, for example by releasing chemicals toxic to fish. And when the algae die and sink, the microbes that work to decompose the blooms in the depths soak up oxygen from the surrounding water.
农业用地土壤中施加的肥料和其他营养物质进入河流并最终汇入沿海水域，导致问题越来越严重。对藻类来说，这些意外而来的食物让它们迅速生长繁殖，形成大片藻华——有时称绿潮或赤潮。藻华会带来很多问题，如释放对鱼类有毒的化学物质等。藻类死亡后沉入深海，分解藻华的微生物也会消耗周围水中的氧。
In severe cases, dissolved oxygen levels can fall so low that parts of the deep ocean become barren. A 2008 global survey found at least 405 of these dead zones, up from 49 in the 1960s. Perhaps most affected is the Baltic Sea. Despite efforts to limit agricultural run-off from surrounding countries, the Baltic still has a massive dead zone of about 70,000 square kilometres – about the size of Ireland.
严重情况下，溶氧量可能大幅下降，导致深海部分地区成为不毛之地。2008年一项全球调查发现至少有405处这样的死亡区，而上世纪60年代仅有49处。受影响最大的也许是波罗的海。尽管努力限制周边国家的农业径流，但波罗的海仍有约7万平方公里的大面积死亡区——与爱尔兰面积相当。
6. Marine food chain collapse
6. 食物链崩溃
Already under pressure from overfishing and pollution, marine life – from large fish down to cyanobacteria – is also affected by climate change. As seas warm and currents shift, some sea life can simply move, for example towards the cooler water of the poles. These shifts in distribution have knock-on effects for species that feed on them: from people trying to catch tuna, to fish looking for zooplankton. Under stress from shifting resources, species are especially vulnerable if they are already weakened by acidification and oxygen depletion.
大到大型鱼类，小到蓝藻，已经面临过度捕捞和污染压力的海洋生物又受到气候变化的影响。随着海洋变暖和洋流移动，一些海洋生物开始向海水温度较低的两极迁移。这些分布上的变化给以它们为食的物种（从试图捕捞金枪鱼的人类到寻找浮游动物的鱼类）带来了连锁反应。对于那些已经遭受海水酸化、氧枯竭打击的物种而言，资源转移的压力更让它们不堪重负。
Changes to interconnected and complex systems of food webs are hard to predict. Fisheries in some areas might actually get a boost as valuable new species are driven into their nets. But, overall, the impact is likely to be bad. A study last year suggested that warmer waters had reduced the total amount of fish that can be caught in a sustainable way by 4% since the 1930s. The worst-affected sea was the Sea of Japan, with a 35% reduction in fishery size due to warming. The East China Sea saw a drop of 8%.
食物网络错综复杂，任何变化都会带来难以预测的结果。有些地方的渔业可能会因为出现了新的高价鱼类而受益匪浅。但总体而言，这些变化带来的影响很可能是负面的。去年的一项研究表明，上世纪30年代以来，海水变暖已经导致可以通过可持续方式捕获的鱼类总量减少了4%。受影响最严重的是日本海，气候变暖导致当地渔业规模缩小35%，中国东海则下降8%。
Future drops in fish catches would threaten the food security of a large fraction of the world’s growing population. According to the UN, fish provide more than 3.1 billion people with at least 20% of their animal protein. It’s an important source of fatty acids and micronutrients too. Fish currently supply 17% of all the protein consumed in the world, and demand is expected to continue to increase as incomes rise in the developing world.
随着全球人口不断增长，未来渔获量下降将威胁大部分人口的粮食安全。联合国数据显示，鱼类为31亿多人口提供了至少20%的动物蛋白。鱼类还是脂肪酸和微量营养元素的重要来源。目前全球消耗的蛋白质有17%来自鱼类，随着发展中国家收入的增长，鱼类需求预计将继续增加。
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