[defrost]

So human activity accounted for 84% of ignitions of 'significant' fires within coterminous United States during the twenty one year period [1992-2012] (inclusive).

Those fires ignited as a result of human activity accounted for 44% of total area burned.

Human activity as a source of ignition includes

> a variety of sources, including the US Forest Service-designated categories of equipment use, smoking, campfire, railroad, arson, debris burning, children, fireworks, power line, structure, and miscellaneous fires.

I'd suggest that it's important to point out that more than half of wild area burned doesn't result from human activity and that human arson is a small portion of human ignition sources (which is not at all how your intial comment reads).

I do agree that the biggest issue here is the effect of changing climate increasing the chances of wildfires both in areas traditionally prone and in areas that have rarely seen them.