Caribou and Reindeer

Caribou and reindeer are classified by scientists as the same species, with the domesticated reindeer dispersed across parts of Europe and Asia and the wild caribou found in North America and Greenland.

Global warming will most harm the animals adapted to the coldest environments, primarily those accustomed to life in the Arctic.

That group includes these large mammals, which have become symbols of Christmas. Their insulated fur and lack of sweat glands allow them to survive harsh winters, but those adaptations also make longer, hotter summers very difficult to endure.

Penguins

The rapid melting of sea ice is a main reason that animals in the polar regions are most affected by even slight warming.

The open-ocean species are doing okay. So the penguins in Antarctica that feed in the open ocean are doing okay; the penguin species that feed by just dropping off the ice shelves, like the Adelie and the emperor （pictured）, are declining.

Musk oxen

Musk oxen are large mammals that have been around since well before the last ice age. They are adapted to live in the coldest of habitats, and Graham says they may be significantly endangered as global warming shrinks their distribution ranges.

Longer, warmer summers could have a devastating impact on their already small populations scattered across northern Canada, Greenland, and parts of Alaska.

Seabirds

As fish move north in search of cooler waters, animals that rely on fish for sustenance are left without many options. This group includes seabirds like the Atlantic puffin （pictured）, the tufted puffin in the North Pacific, and the rhinoceros auklet.

Seabirds that rely on plankton are also struggling to find food. Warm surface temperatures and upwellings and downwellings cause the plankton to descend to lower depths, out of reach of surface-feeders.

During a food shortage, many animals do not breed very well or, in some cases, at all. Disruptions in the mating patterns of several species of seabird have been reported across the globe. Some have been laying their eggs later and experiencing fewer successful hatchings.

Possums

Along with arctic animals, species that reside on mountaintops are also experiencing the effects of warming. Parmesan says tree possums that reside in high elevations are particularly in danger.

There's a group that's restricted to high elevations, and the white lemuroid possum （pictured）, which is among this group, has not been seen since 2005, and it's believed to be the first mammal driven extinct by climate change.

驯鹿与北美驯鹿

科学家们把驯鹿与北美驯鹿归为同一物种。驯化的驯鹿分布在亚洲和欧洲部分地区，而野生的北美驯鹿则生活在北美和格陵兰岛。

全球变暖对已经适应最寒冷环境的动物，主要是那些习惯了北极生活的动物造成的伤害最严重。

这些动物中就包括驯鹿，这种大型动物已经成为圣诞节的标志。它们有保温的皮毛，并且缺乏汗腺，这使它们能够在冬天的严寒中生存，但也使更长、更炎热的夏天变得难以忍受。

企鹅

即使气温稍有升高，两极地区的动物也会受到影响，这主要是由海上冰层的快速融化造成的。

远海带（开阔海域）物种对这种变化还比较适应。因此，在南极洲远海带捕食的企鹅适应得比较好，而只靠从冰架上跃入水中捕食的阿德利企鹅和帝企鹅（如图所示）则面临衰落。

麝香牛

早在最后一次冰河时期之前，麝香牛这种大型动物就已经遍布世界各地了。它们已经适应了在最冷的地方栖息。格雷厄姆说，随着全球变暖不断侵蚀它们的分布范围，麝香牛可能面临严重的灭绝危机。

更长、更炎热的夏季可能会对分散在加拿大北部、格陵兰岛和阿拉斯加部分地区本已为数不多的麝香牛带来毁灭性的打击。

海鸟

随着鱼群为了寻找更冷的水域而向北迁移，靠捕鱼维持生计的动物们也没有更多选择了。这些动物中就包括大西洋海雀（如图所示）、北太平洋善知鸟和犀角海雀等海鸟。

靠浮游生物为生的海鸟也越来越难找到食物了。升高的水面温度、上升水流和下降水流使浮游生物下沉到更深的地方，在水面捕食的动物已无法触及。

在食物短缺时，很多动物的繁殖情况很差，有时甚至完全不繁殖。世界各地都出现了关于某些种类的海鸟交配模式被破坏的报道。有些海鸟产卵期推迟了，孵化率也变得更低。

负鼠

和北极圈的动物一样，生活在山顶地区的物种也受到了气候变暖的影响。帕玛森说，生活在高海拔地区的树负鼠境遇尤其危险。

有些物种生活的环境仅限于高海拔地区，白狐猴负鼠（如图所示）就是其中一种。从2005年开始，就再也没有人发现过它们的踪迹，人们相信这是由于气候变化而灭绝的第一种动物。