Muck in Arctic lake sends a signal

If Earth were behaving the way we have all grown up expecting, its climate swaying to the timeless rhythms of its orbital path around the sun, the Arctic would not be warming.  Its sea ice would not be thinning and there would be no talk of an Arctic of "ice-free summers" or a Northwest Passage anytime soon.

If astronomical circumstances were still in charge, the Arctic would be 8,000 years along the path of a 12,000-year cooling trend. That pace and direction of natural variability is driven by a wobble in the planet's tilt in relation to the sun, a well-known cycle that completes itself every 21,000 years or so.

While the energy of sunlight striking the far north continues to decline, the character of the Arctic climate has abruptly changed. According to new study published in the Proceedings of the National Academy of Sciences, the change began to show up about 1950 in sediment cores recently extracted from the bed of a small lake on the east coast of remote Baffin Island, west of Greenland.

"The past few decades have been unique in the past 200,000 years in terms of the changes we see in the biology and chemistry recorded in the cores," said Yarrow Axford, a University of Colorado-Boulder researcher and lead author of the study.  "We see clear evidence for warming in one of the most remote places on Earth at a time when the Arctic should be cooling because of natural processes."

The researchers say the change was signaled by the abrupt decline in the abundance of several types of mosquito-like midges that flourish in very cold climates.  Two species of the cold-loving midges have completely disappeared from the sediment cores.  At the same time, a species of diatom, a lake algae shown here in an electron microscope image courtesy of Canadian researcher Cheryl Wilson, has abruptly increased, possibly a result of declining ice cover on the lake.

Perhaps you want to ask, what exactly does the minute contents of the muck in the bottom of a remote Arctic lake have to do with anything important to those of us living in the temperature zones of the Northern Hemisphere?  No one can say exactly, of course.  That's not the way science works -- or Earth.  One thing is certain, though.  If this abrupt climate change turns out to be a singular, benign episode without serious portent for the rest of the planet, a lot of earth scientists are going to be surprised.