Large, empty vessels may be the noisiest, but it is often the tiny things that have most to say. This is especially true when it comes to understanding ancient environments. Every sea shell has a story to tell if you’re listening, as They Might Be Giants once sang.

In the case of global warming, that vast pool of vitriol and vilification, the silent miniatures go by the name of diatoms.

Microscopic algae with skeletons made of glass, diatoms live anywhere water is present. Oceans are ideal, but a garden pond will do; even moist soil is sufficient for some species. Combine this abundance with their preservable silica shells, and diatoms become pretty much the perfect organisms for studying environmental change.

In the frigid pond sediments of northern Canada, diatoms in each layer record the lake conditions at the time the mud was deposited. The layers go back millennia, giving the history of the lake.

The diatom champion and lake historian is Professor John Smol of Queen’s University, Kingston.  In the 1980s and ’90s, Smol and his colleagues realized that diatoms were telling us an alarming story of Arctic climate change.

There is no climate change ‘conspiracy’

Will consensus ever be reached over global warming? Of course not. Agreement is impossible with so many vested interests from so many groups, and such skepticism and misunderstanding. The idea, however, that there is a scientific conspiracy taking place could only be thought up by people utterly ignorant of how science works.

Most scientists enjoy nothing more than a bit of one-upmanship, of finding data that disproves a colleague’s widely held hypothesis, or of attacking someone else’s theory if they think the interpretation is dubious. If a theory gains credence it is not because it is being falsely supported, but because it is robust.

So Arctic lake ecosystems are being changed by global warming linked to the anthropogenic burning of hydrocarbons. Should we care? Does it matter if the ice melts and the lakes dry up?

Just ask Professor Smol. When he analyzed the lake sediments of the Canadian High Arctic, he found the same diatom species had dominated the ecosystems for thousands of years. Then, in the middle of the 19th century, an extraordinary change had taken place: the cool-water species were replaced abruptly by warmer-water ones. In the older records, these sun-seekers were always there, but always rare. Suddenly, they were everywhere.

Smol’s conclusion?  Arctic warming as a consequence of the Industrial Revolution, causing ice cover to melt, providing more habitat for the warmer-water diatoms.

What a storm

Well, what a storm brewed up. Dissenting voices piped up from all corners against the idea. Anthropogenic climate change couldn’t be to blame, they argued, for a whole lakeload of reasons, not least what the ponds of Labrador and northern Quebec indicated. There, the diatom records were different, showing no change in favour of warm-water species. Surely that proved global warming wasn’t responsible? The changes must be due to something else: lake pollution, perhaps, or altered nutrient levels.

Smol and his team re-examined their hypothesis. Arctic lakes used for dumping sewage showed a dramatic increase in nutrients, but minimal change in diatoms; others showed a dramatic shift in the diatoms, but not in the nutrients. No link there.

Pollutants couldn’t explain the patterns either: Labrador’s ponds were full of recent, noxious chemicals, but the diatoms that lived there before the pollution were still living there after.

But should we care?

Perhaps the neatest of all Smol’s proofs was a study of two lakes, immediately adjacent to one another. Their waters were the same, their pollutant levels the same, their nutrient levels the same, but one was mostly shaded from the Arctic summer sun, whilst the other wasn’t. If climate was the driving mechanism of ecological change, the two otherwise identical lakes would show different patterns, the shady lake retaining its cool-water diatoms, and the sunny lake next door acquiring warmer-water species. And the analysis revealed exactly that.

Labrador’s climate is strange anyway. Regional temperature trends have shown that the icy Labrador Current drifting down the coast from Baffin Bay has kept the area disproportionately cold, whilst the rest of Arctic Canada has heated up.  Or at least, that was the case.  Recent studies show that the Labrador Current is warming too, and the region’s ponds are getting increasingly de-iced during the summer.  The warmer-water diatoms are beginning to dominate.

So Arctic lake ecosystems are being changed by global warming linked to the anthropogenic burning of hydrocarbons. Should we care?  Does it matter if the ice melts and the lakes dry up?  If you’re not a diatom, it might all seem irrelevant, but the Earth is an integrated network of feedbacks and knock-on effects.  What happens in the Arctic affects the rest of the world.  As John Smol emphasizes, these high-latitude environments are the world’s “canary in the coal mine.”

And if you don’t know what it means when that canary keels over, you’re probably in trouble.