A walk across Alaska's Arctic sea ice brings to life the losses that appear in climate data

徒步穿越阿拉斯加的北极海冰，让气候数据里呈现的损耗变得真切可感。

This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.

本文最初发表于《对话》网站。该出版物将此文投稿至太空网（Space.com）的《专家之声：评论与洞见》栏目。

As I walked out onto the frozen Arctic water off Utqiagvik, Alaska, for the first time, I was mesmerized by the icescape.

当我第一次踏上阿拉斯加乌特恰维克附近冰封的北极水域时，我被这片冰景深深吸引。

Piles of blue and white sea-ice rubble several feet high gave way to flat areas and then rubble again. The snow atop it, sometimes several feet deep, hides gaps among the blocks of sea ice, as I found out when one of my legs suddenly disappeared through the snow.

几英尺高的蓝色和白色海冰瓦砾堆让位于平坦的区域，然后又是瓦砾堆。它上面的雪，有时有几英尺深，隐藏着海冰块之间的缝隙，当我的一条腿突然消失在雪地里时，我发现了这一点。几英尺高的蓝白海冰碎块堆，先是过渡到平坦区域，接着又变回碎冰堆。冰面之上的积雪有时深达数英尺，掩盖了海冰块之间的缝隙——我亲身体会到这一点时，一条腿突然陷进了雪层里。

As a polar climate scientist, I have focused on Arctic sea ice for over a decade. But spending time on the ice with people who rely on it for their way of life provides a different perspective.

作为一名极地气候科学家，我十多年来一直专注于北极海冰研究。但与依赖海冰生存的人们一同在冰面上相处，让我获得了截然不同的视角。

Local hunters run snowmobiles over the sea ice to reach the whales and seals they rely on for traditional food. They talked about how they know when the sea ice is safe to travel on, and how that's changing as global temperatures rise. They described worsening coastal erosion as the protective ice disappears earlier and forms later. On land, they're contending with thawing permafrost that causes roads and buildings to sink.

当地猎人驾驶雪地摩托在海冰上穿行，去捕猎作为传统食物来源的鲸鱼和海豹。他们讲述了自己如何判断海冰是否适合通行，以及随着全球气温上升，这种判断方式又发生了怎样的变化。他们描述道，由于起到保护作用的海冰消融得更早、形成得更晚，海岸侵蚀问题正不断加剧。在陆地上，他们还在应对永久冻土融化带来的问题——冻土融化导致道路和建筑下沉。

Their experiences echo the data I have been working with from satellites and climate models.

他们的亲身经历，与我一直在研究的卫星数据和气候模型数据相印证。

Most winters, sea ice covers the entire surface of the Arctic Ocean basin, even extending into the northern North Atlantic and North Pacific. Even in late summer, sea ice used to cover about half the Arctic Ocean. However, the late summer ice has declined by about 50% since routine satellite observations began in 1978.

大多数冬季，海冰会覆盖北冰洋盆地的整个表面，甚至延伸至北大西洋北部和北太平洋区域。即便到了夏末，北极海冰过去也能覆盖北冰洋约一半的面积。然而，自1978年卫星常规观测启动以来，夏末的海冰面积已经减少了约50%。

This decline of summer sea ice area has a multitude of effects, from changing local ecosystems to allowing more shipping through the Arctic Ocean. It also enhances global warming, because the loss of the reflective white sea-ice surface leaves dark open water that absorbs the sun's radiation, adding more heat to the system.

夏季海冰面积的减少引发了诸多影响：既改变了当地的生态系统，也让更多船只得以穿越北冰洋；同时还加剧了全球变暖——因为具有反射性的白色海冰表面消失后，露出的深色开阔水域会吸收太阳辐射，给整个气候系统增加更多热量。

Along the Alaskan coast, the decline of the Arctic sea ice cover is most apparent in the longer ice-free season. Sea ice is forming later in the fall now than it used to and breaking up earlier in the spring.

在阿拉斯加海岸沿线，北极海冰覆盖面积的减少，在更长的无冰期里体现得最为明显。如今海冰在秋季形成的时间比以往更晚，在春季破裂的时间却更早。

For people who live there, this means shorter seasons when the ice is safe to travel over, and less time when sea ice is present to protect the coastline from ocean waves.

对于生活在那里的人们而言，这意味着冰面可安全通行的季节变得更短，海冰能保护海岸线免受海浪侵袭的时间也随之减少。

Open water increases the risk of coastal erosion, particularly when accompanied by thawing permafrost, stronger storms and rising sea level. All are driven by greenhouse gas emissions from human activities, particularly burning fossil fuels.

开阔水域增加了海岸侵蚀的风险，尤其是当同时出现永久冻土融化、风暴加剧和海平面上升的情况时。这些现象均由人类活动产生的温室气体排放所致，其中化石燃料的燃烧是主要原因。

In some places along the Alaskan coast, erosion threatens roads, houses and entire communities. Research has shown that coastal erosion in Alaska has accelerated over recent decades.

在阿拉斯加海岸的部分地区，侵蚀正威胁着道路、房屋乃至整个社区。研究表明，近几十年来阿拉斯加的海岸侵蚀速度一直在加快。

More weeks of open water also affect animals. Polar bears spend the summer on land but require sea ice to hunt their preferred food, seals. The longer the sea ice stays away from land, the longer polar bears are deprived of this high-fat food, which can ultimately threaten the bears' survival.

更长时间的开阔水域也对动物造成了影响。北极熊夏季会在陆地上生活，但它们需要海冰来捕猎自己最喜爱的食物——海豹。海冰远离陆地的时间越长，北极熊被剥夺这种高脂肪食物的时间就越久，这最终会威胁到它们的生存。

Across the Arctic, satellite data has captured how sea ice has been thinning and getting younger.

在整个北极地区，卫星数据记录下了海冰不断变薄、“年龄”也越来越小的变化过程。

As recently as the late 1970s, about 60% of the Arctic sea ice was at least 1 year old and generally thicker than younger ice. Today, the amount of ice more than a year old is down to about 35%.

就在20世纪70年代末，约60%的北极海冰形成时间至少有一年，而且通常比新形成的海冰更厚。如今，形成时间超过一年的海冰占比已降至约35%。

Local residents experience that change in another way: Multiyear sea ice is much less salty than new sea ice. Hunters used to cut blocks of multiyear sea ice to get drinking water, but that older ice has become harder to find.

当地居民以另一种方式感受到了这种变化：多年海冰的盐度远低于新海冰。猎人们过去常常切割多年海冰来获取饮用水，但如今这种老冰已经越来越难找到。

Sea ice forms from ocean water, which is salty. As the water freezes, the salt collects in between the ice crystals. Because the higher the salt content, the lower the freezing point of the water, these enclosures in the sea ice contain salty liquid water, called brine. This brine drains out of the sea ice over time through small channels in the ice. Thus, multiyear sea ice, which has survived at least one melt cycle, is less salty than first-year sea ice.

海冰由含盐的海水形成。当海水结冰时，盐分聚集在冰晶之间。由于含盐量越高，水的冰点就越低，海冰中的这些空隙里会留存着含盐的液态水（称为卤水）。随着时间推移，这些卤水会通过冰中的细小通道排出海冰。因此，至少经历过一次融化周期的多年海冰，盐度要低于一年冰。

Since the coastal landfast sea ice around Utqiagvik no longer contains much multiyear sea ice, if any, the hunters now have to take a block of lake ice or simply gallon jugs of water with them if they plan to stay on the ice for several days.

由于乌特恰维克周边的沿岸固定海冰中，即便还有多年海冰，数量也已极少，所以猎人们如果打算在冰面上停留数日，现在就必须带上一大块湖冰，或者直接带上加仑装的水壶。

As long as greenhouse gas emissions continue to increase, Arctic sea ice will generally continue to decline, studies show. One study calculated that, statistically, the average carbon dioxide emissions per person per year in the U.S. led to the disappearance of an area of summer sea ice the size of a large hotel room – 430 to 538 square feet (40 to 50 square meters) each year.

研究表明，只要温室气体排放量持续增加，北极海冰的覆盖范围总体上就会继续缩减。有一项研究经统计计算得出，美国人每年人均二氧化碳排放量，会导致每年有一个大型酒店房间大小（430至538平方英尺，即40至50平方米）的夏季海冰消失。

Today, when Arctic sea ice is at its minimum extent, at the end of summer, it covers only about half what it covered in 1979 at that time of the year. The Arctic still has around 1.8 million square miles (4.6 million square kilometers) of sea ice that survives the summer melt, approximately equal to the area of the entire European Union.

如今，夏末北极海冰覆盖面积降至全年最低值时，其范围仅为1979年同期的一半左右。北极仍有约180万平方英里（460万平方公里）的海冰能熬过夏季融化期，这一面积大致相当于整个欧盟的国土面积。

Climate models show the Arctic could be ice-free at the end of summer within decades, depending on how quickly humans rein in greenhouse gas emissions.

气候模型显示，北极可能会在几十年内迎来夏末无冰的状况，具体取决于人类控制温室气体排放的速度。

While a win for accessibility of shipping routes through the Arctic in summer, studies suggest that the large reduction of sea ice would bring profound ecological changes in the Arctic Ocean, as more light and heat enter the ocean surface.

尽管夏季北极航道的通行便利性因此提升，但研究表明，海冰的大幅减少会给北冰洋带来深刻的生态变化——因为会有更多的光线和热量进入海洋表面。

The warmer the surface ocean water is, the longer it will take for the ocean to cool back down to the freezing point in the fall, delaying the formation of new sea ice.

表层海水温度越高，秋季海洋冷却至冰点所需的时间就越长，这也会推迟新海冰的形成。

Arctic sea ice will continue to form in winter for the next several decades. The months of no sunlight mean it will continue to get very cold in winter, allowing sea ice to form.

在未来几十年里，北极海冰仍会在冬季形成。冬季长达数月的极夜会让气温持续走低，为海冰的形成创造了条件。

Climate models have estimated that it would take extremely high atmospheric carbon dioxide concentrations to warm the climate enough for no sea ice to form in the winter in the Arctic Ocean – close to 2,000 parts per million, more than 4.5 times our current level.

气候模型估算显示，要让气候变暖到北冰洋冬季不再形成海冰的程度，需要大气中二氧化碳浓度达到极高水平——接近2000ppm（百万分之一），这一数值是当前浓度的4.5倍以上。

However, winter sea ice will cover less area as the Earth warms. For people living along the Arctic Ocean coast in Alaska, winter ice will still return for now. If global greenhouse gas emissions are not reduced, though, climate models show that even winter sea ice along the Alaskan coast could disappear by the end of the 21st century.

然而，随着地球变暖，冬季海冰的覆盖面积会不断缩小。对于生活在阿拉斯加北冰洋沿岸的人们来说，目前冬季海冰仍会如期出现；但如果全球温室气体排放量得不到削减，气候模型显示，就连阿拉斯加海岸的冬季海冰也可能在21世纪末消失。

This article is republished from The Conversation under a Creative Commons license. Read the original article.

本文依据知识共享许可协议，转载自《对话》网站。点击阅读原文。