My company runs a snow play area north of Flagstaff, Arizona. One of the problems with this location is that the main sledding runs are on a black cinder hill. Covered in snow, this is irrelevant. But once the smallest hole opens up to reveal the black cinders underneath, the hole opens and spreads like crazy. The low albedo cinders absorb heat much faster than reflective white snow, and then spread that heat into the snow and melts it.
Anthony Watt does an experiment with ash and snow in his backyard, and the effects are dramatic.
Even tiny amounts of soot pollution can induce high amounts of melting. There is little or no ash at upper right.. Small amounts of ash in the lower and left areas of the photo cause significant melting at the two-hour mark in the demonstration.
I won't steal his thunder by taking his pictures, but you should look at them -- as the saying goes, they are worth a thousand words.
We know that Chinese coal plants pump out a lot of black carbon soot that travels around the world and deposits itself over much of the norther hemisphere. We can be pretty sure a lot of this carbon ends up on the Arctic ice cap, and as such contributes to an acceleration of melting.
I'v tried to do a thought experiment to think about what we would expect to see if this soot was driving a measurable percentage of Arctic ice melt. It seems fairly certain that the soot would have limited effects during the season when new snow is falling. Even a thin layer of new snow on top of deposited carbon would help mitigate its albedo-reducing effect. So we would expect winter ice to look about like it has in the past, but summer ice, after the last snowfalls, to melt more rapidly in the past. Once the seasons cool off again, when new ice is forming fresh without carbon deposits and snow again begins to fall, we would expect a catch-up effect where sea ice might increase very rapidly to return to winter norms.
Here is the Arctic ice chart from the last several years:
Certainly consistent with our though experiment, but not proof by any means. The last 2 years have shown very low summer ice conditions, but mostly normal/average winter extent. One way we might get some insights into cause and effect is to look at temperatures. If the last 2 years have had the lowest summer sea ice extents in 30 years, did they have the highest temperatures?
Not really, but it may have been past warming has had a lag effect via ocean temperatures.
The point is that I am not opposed the idea that there can be anthropogenic effects on the climate, and it looks like black carbon deposits might have a real negative impact on sea ice. If that were the case, this is really good news. It is a LOT easier and cheaper to mitigate black carbon from combustion (something we have mostly but not completely done in the US) than it is to mitigate CO2 (which is a fundamental combustion product).