interesting climate mystery,

an historic mystery. This is a story about how people affect the

environment in many ways,

sometimes unexpectedly. This is what we strive to understand at CIRES.

So here's the mystery: Glaciers in the Alps began to retreat abruptly in the

1860s,

but it was cold in the region, still cold after a few centuries of a

Little Ice Age in Europe. Now the Industrial Revolution had

just begun in the 1860s, with factories burning coal and other

fuels in earnest.

It was too soon for that activity to have caused enough greenhouse warming to melt

the glaciers.

So the scientists figured there must be something else going on, something that

could melt the snow.

Soot or black carbon from those factors popping up in Western Europe might do it, the team figured.

The researchers began to dig into what was known about how much black carbon was in the

air back in the 1860s

Soot, when it lands on snow, can absorb sunlight and cause melt.

With models and observations of soot in snow and ice layers, they showed that

when you account for the effect of soot on snow,

the glacial retreat in the 1860s was no longer surprising.

It was an expected consequence of human activity.