According to an American team of climate modelers and their peer-reviewed article in Journal of Geophysical Research, about 0.1-0.15 Celsius degrees of warming in the last two centuries is due to
which is up to 19% of the "global" warming. The effect is strongest in the Arctic. They argue that 0.5C out of 1.6C warming in the Arctic (one third) should be attributed to dirty snow i.e. snow polluted by even small amounts of black carbon: 80% of this black carbon comes from human activity. In the Arctic region itself, dirty snow would thus have the same impact as the enhanced greenhouse effect (click the picture below).
I can't check the numbers but you can see how "settled" this science is. Within a few days, 20% of the warming is attributed to a previously unknown effect even though this effect intuitively seems much more important than e.g. the greenhouse effect. According to these and other current "official" numbers, dirty snow has contributed more to the warming than e.g. enhanced greenhouse effect from the whole global transportation or than enhanced greenhouse effect from the whole global energy production. Be sure that dirty snow is not the last contribution that is going to be found.
Puppets made out of dirty snow
The U.S. scientists also act as activists and urge Canada to lead the cleanup efforts and to be careful with the Northern Passage.
Alexander Cockburn has another powerful critical analysis of the climate change orthodoxy from a left-wing perspective in The Nation and Counterpunch. For example, he writes:
The left has been swept along, entranced by the allure of weather as revolutionary agent, naïvely conceiving of global warming as a crisis that will force radical social changes on capitalism by the weight of the global emergency.