Sediment cores taken from a remote Arctic lake indicate that the ecosystem has changed dramatically in recent decades, according to a new study.

These shifts, which are unprecedented for the past 200,000 years, most likely result from human-induced climate change.

Writing in the Proceedings of the National Academy of Sciences, the authors explain that ecosystem changes as observed in sediment cores are tightly linked to changes in climate.

Until quite recently, natural influences, such as periodic shifts in Earth's orbit, effected the  changes. But the ecosystem shifts they observe since 1950 indicate that something other than Earth's wobbly orbit is changing the Arctic's climate.

As another recent study pointed out, going strictly by orbital shifts, the Arctic should be cooling at present. Earth is now 0.6 million miles farther from the sun during the northern hemisphere's summer solstice than 2,000 years ago, and receives less of its energy.

And, in fact, the Arctic was gradually cooling for the past 2,000 years — until about 50 years ago when, despite the diminished solar energy reaching the northern hemisphere during summer, it abruptly began warming. (Here's a nice graphic of that trend and its abrupt reversal.)

And the Arctic lake ecosystem appears to have adjusted accordingly.

The authors of the PNAS study examined the relative abundances of midges and algae in the sediments of a lake on Baffin Island, which lies a few hundred miles west of Greenland. For the past several thousand years, cold-adapted midge larvae have abounded in the lake.

Then came 1950. Since then, midge numbers have undergone a steep decline. Two species have disappeared entirely.

In that same period, a lake alga species, which was relatively scarce before the 20th century, has increased in abundance. The authors attribute this to less lake ice. Without it, the photosynthetic alga has more access to sunlight.

This study comes on the heels of a several others documenting other ecosystem shifts in the Arctic. A review last month in Science summed them up. In the past 150 years, Earth's average temperature has increased by about 0.4 C (0.72 F.).

Page: 1 | 2