Imagine a caribou, a female, pregnant.

She is a beautiful animal. Among all female deer, only her domesticated cousin, the reindeer, grows antlers like she does. And what antlers! Tall and branching, they are lined with a thin velvety layer, like the neck of a mallard. On cave walls, in the heart of Europe, it is possible to find vivid portraits of caribou. Some are more than 15,000 years old.

Like the woolly mammoths, the caribou were among the Pleistocene's most prolific large mammals. But unlike the woolly mammoths, the caribou survived the megafauna extinction that coincided with the Pleistocene’s melt, and the emergence of modern humans. The spear-wielding primates came for the caribou, too. Did they ever. But somehow, the caribou were spared.

No one is quite sure why, though acclimation to extreme cold is surely part of the story. The caribou makes its home on the Arctic’s tundras, in Scandinavia, Siberia, Alaska, Northern Canada, and Greenland. It makes its home in frigid places, where few mammals can live.

Those places are shrinking now. Human beings have wrapped the planet in a sphere of technology, powered by fossil fuels, whose exhaust is pooling in Earth’s atmosphere, transforming it into a toxic steambath.

Earth’s climate has changed constantly during the 4 billion years that life has lived on this planet. But usually, it changes slowly. When the climate has changed quickly, species that failed to adapt died off, often in shocking numbers. The quickly warming Arctic is now forcing caribou to adapt.

The caribou breeding cycle is timed to the sun, not to temperature. It is timed so that baby caribou will be born during late May or early June, every year, without exception. Plants are different. They time their growth cycle to the temperature. They can be awakened early.

Before the Arctic started warming, these two cycles were in sync. A pregnant caribou could count on there being plenty of nutrient-rich vegetation around in May, when she needed it most, to feed the single baby calf growing within her.

Climate change is decoupling these cycles. Plants are erupting out of the ground earlier in the year. By the time pregnant caribou arrive at their birthing grounds, the vegetation has already peaked. Mothers are becoming malnourished. Fewer calves are being born, and fewer are surviving their crucial first few months. And even when they do survive, they are still vulnerable, to overhunting, and to diseases carried north by deer that would never have survived the Arctic chill of yesteryear.

Caribou populations are reeling. And now they face a new menace, from mosquitoes, according to a new paper from a team led by Lauren Culler, a postdoc at the Dickey Center’s Institute for Arctic Studies at Dartmouth.

Culler spent the summer of 2011 and the summer of 2012 studying mosquitoes in Kangerlussuaq, a small town on the west coast of Greenland. “It was a warm year in 2012,” Culler told me, in a phone interview. “The ponds where mosquitoes breed melted earlier.”

Mosquitoes responded to this early melt by hatching ahead of schedule. They also grew faster, meaning they spent less time in the vulnerable, developmental state that makes them easy prey for birds. More of them survived to adulthood, and that’s bad news for caribou.

Arctic mosquito swarms are the stuff of legend. Some of them contain hundreds of thousands, if not millions, of insects. That's enough to harass a pregnant caribou until she stops worrying about food. And it's enough to kill caribou calves outright.

Things will likely get worse for the caribou before they get better. Culler brought some of the mosquitoes into a lab at the Kangerlussuaq International Science Support building. She placed the mosquitoes into water that was slightly warmer, in order to simulate the Arctic ponds of the near future. They hatched earlier and grew faster, still.

If the Arctic continues to warm, and there is every indication that it will, the summer tundra may soon be abuzz with larger and larger clouds of biting, blood-sucking insects.

“Caribou have no defense against mosquitoes,” Culler told me, “except to run.”

But where will they run to? Rising temperatures are steadily encroaching on caribou habitats, and so are roads and pipelines. Wildlife corridors are narrowing. Climate change is too small and too neat a narrative. It doesn’t quite capture what’s happening in the Arctic, and elsewhere. This is planetary change, and its butterfly effects are only beginning.