https://share.america.gov/wp-content/uploads/2015/06/2011-NASA-Kathryn-Hansen-700x466.jpg北极变暖正在给航运和油船打开新航道。(NASA/K. Hansen)

2015年，北美经历了异常的冬季。美国一些历来天寒地冻的地区出现了创纪录的温暖天气，而另一些地区的降雪量则达到几乎历史空前。

中亚地区以及英国和其他一些欧洲国家近年也遭遇了极其异常的冬天。

虽然科学家不能将某个气候事件与全球气候变化直接挂钩，但他们发现，已经得到大量记载的北极升温现象，正在给地球热带以北和北极以南之间的温带地区造成气候异常。

美国国家海洋与大气层管理局卫星应用及研究中心（NOAA’s Center for Satellite Applications and Research）的卫星科学家杰夫·基（Jeff Key）说，“北极出现的现象不停留在北极。”

杰夫·基专注研究卫星采集的风、化学元素、温度和湿度的图像和数据，而所有数据都正在偏离历史正常值。他说，这些说明北极大气层正在变化。

杰夫·基指出，“有重要意义的是，这影响到中纬度的气候”。换句话说，北极的变化会对在地球上空6公里以上的大气层中从西向东旋转的庞大气流产生影响。“由于气流减弱，它会出现更多的来回飘移，从而在中纬度地区形成更多极端天气。

其他一些科学观察显示，北冰洋（Arctic Ocean）的冰面减小，这意味着北冰洋会比过去更多地吸收热，而它的热反射强度降低。

杰夫·基说，“我认为海冰减少肯定会给气候规律带来改变，打开航运通道以及对石油和天然气的探索。美国海军也预见到类似的变化。

“世界将要有不同的面貌。“

永冻苔原也在变暖，那里的植被正在改变。杰夫·基说，绿色植被的生长会改变这些地带对阳光的折射力，因此“植被的变化可能导致气候更暖，而气候更暖可能导致植被的更大变化，如此循环”。

永冻苔原的融化还意味着，基于原先被认为是永冻地基上的基础设施如今会失去稳定性。

杰夫·基和全球科研人员正在继续努力了解北极地区的复杂生态，而最近期的研究显示，北极的变化将产生深远影响。

杰夫·基说：“我认为，20、30、40年后世界将要有不同的面貌。”

2014年年底发布的《北极年度报告》（Arctic Report Card）指出，北极正在以比世界其他地区快一倍的速度变暖。报告列举了北极生态系统出现的许多变化。

美国国务卿约翰·克里（John Kerry）在美国于四月接任八国北极理事会（Arctic Council）主席时提醒人们，全球必须保护、尊重、呵护北极。

North America’s winter of 2015 defied the norms. Normally frigid areas of the United States had record warmth, but historic snowfalls buried other parts of the country.

Central Asia, the United Kingdom and other European nations also experienced weird winters in recent years.

Though scientists can’t draw direct links between single weather events and global climate change, they find that widely documented Arctic warming is causing unusual weather in the temperate zones north of the tropics, south of the Arctic.

“What happens in the Arctic isn’t staying in the Arctic,” said satellite scientist Jeff Key from NOAA’s Center for Satellite Applications and Research.

He studies satellite imagery and data on winds, chemistry, temperature and humidity. They are all straying from historic norms, and show the Arctic atmosphere is changing, he says.

“What’s important is that this affects midlatitude climate,” Key said. Arctic changes influence the jet stream, giant rivers of air flowing west to east 6 or more kilometers above the Earth.

“As the jet stream weakens, it tends to meander more, and we get more extreme weather in the midlatitudes,” Key said.

Other scientific observations reveal less ice in the Arctic Ocean, which means waters will absorb heat rather than reflect it.

“I think less sea ice is certainly going to change weather patterns, open up [channels] for shipping [and] oil and gas exploration,” Key says. The U.S. Navyforesees similar changes.

“It’s going to be a different world out there.”

The tundra is also warming, and its vegetation is changing. The extent of surface green matter can alter how much sunlight is reflected, so “a change in vegetation can lead to even greater warming, which leads to a greater change in vegetation and so forth,” Key said.

Thawing tundra also means that infrastructure built on what was thought to be perpetually frozen ground can become unstable.

As Key and his scientific colleagues worldwide continue their work to understand the complexities of the northernmost regions, the latest research suggests a changing Arctic will have far-reaching effects.

“It’s going to be a different world out there, I think, in 20, 30, 40 years,” Key says.

The U.S. Arctic Report Card issued in late 2014 found the region is warming at twice the rate of anywhere else on Earth. It documents a broad array of changes in the region.

As the United States took the chairmanship of the eight-nation Arctic Council in April, Secretary of State John Kerry reminded the world it must protect, respect and nurture the region.