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SOURCE: Yale e360

DATE: September 13, 2018

SNIP: From their perch on a rocky ridge in southwestern Greenland, graduate students Rebecca Walker and Conor Higgins peer through binoculars, looking for caribou. It’s a cool, June day and the tundra is ablaze with tiny magenta, pink, and yellow wildflowers. Crystalline lakes dot the glacially carved valleys, and from the round-topped mountains you can catch the glint of the massive Greenland Ice Sheet to the east. Below, the Watson River tumbles toward Kangerlussuaq Fjord, 12 miles to the west. It’s quiet, save for bird song, the rush of the wind, and the frequent crash of ice shearing off nearby Russell Glacier.

Two decades ago, Walker and Higgins would have seen hundreds of caribou from the top of this same hill, set amid an ancestral caribou calving grounds. But these days the herds are a fraction of their former size, and Walker and Higgins spot only a handful of females and two calves a mile away. The ecologist supervising the students — Eric Post of the University of California, Davis — says the decline is very likely linked to a rapidly warming climate that is driving the schedules of caribou and the tundra plants they eat seriously out of balance.

Post first came to the area 25 years ago to study calving in large herds of caribou. But around the early 2000s, he began noticing a major change.

“As it got warmer and warmer and the growth season started earlier and earlier, the caribou calving season wasn’t starting earlier to the same extent,” Post says. The advancing plant growth was being triggered by warmer temperatures early in the season, while the caribou take their cues from the length of day. As a result, studies suggest, the plants may have already passed their nutritional peak by the time the herds arrived to eat them. Post determined that in years with the earliest plant growth, caribou parents produced the fewest calves, and those born were more likely to die young — possible victims of nutritional stress.

The caribou population at the site has declined pretty dramatically since this work began,” he says.

This growing mismatch between peak vegetation growth and the birth of caribou calves shows how phenology — the timing of seasonal events such as plants flowering, birds migrating, insects hatching, and animals giving birth — is being knocked out of balance in our rapidly warming world. In his quarter-century of studying the impacts of global warming on Greenland’s ecosystems, Post, 51, has observed what he calls “dramatic and disturbing” changes in the seasonal clock.

Post’s latest research finds that in the past decade, the onset of spring has moved up four days for every 10 degrees north of the equator. That builds to a 16-day advance on average north of the 59th parallel. And the rate of change appears to be accelerating.

[Read the whole thing; it’s a fascinating article about other species in the Arctic that are now mismatching too].