The original assumption that 20 minutes at ~260 degrees could cause worldwide forest fires is a far jump to begin with. Cut a section out a tree and place it in an oven set at ~260 for 20 minutes and you'll have nothing more than a mildly warm piece of wood, you'll definitely be a long haul from spontaneous ignition.
I've had plenty of camp fires in my time, and fresh wood certainly takes its time before combustion. I have serious doubts that a living tree would be capable of spontaneous ignition within 20 minutes of exposure to heat.
It may have ignighted forest fires in some dry or drought areas, but you're unlikely to spread forest fires in the boreal forests, where wildfires would have had the greatest effect. Forest fires in these regions happen only every 20-200 years, it's unlikely the raise of temperature in these regions would have caused a wildfire in the height of summer if it wasn't reaching one of these periods anyway. If the impact occurred during the winter months you'd have no chance to cause wildfires in these regions, even if the planetary temperature jumped by 260 degrees, the boreal regions would likely still be 20-30 degrees below the ignition point of wood. Considering these places can be 10+ feet deep in snow and ice (which incidentally insulate from heat) there likely wouldn't have been a noticeable effect.
Considering winter in the boreal lasts 5-6 months, there was a 50/50 chance that the impact would only have a negligible effect. Then consider the fact that the boreal has a high density of bogs and lakes means the wood is frequently waterlogged, so the chance of boreal wildfires being ignited gradually become slim-to-none, especially if it was a cold period in the climatic cycles.
For us Americans, note that 260° C = 500° F. I haven't tried the experiment, but given how quickly various foods (including fresh rosemary sprigs and other live plant matter) blacken in an oven that temperature, I wouldn't be surprised at all if it set leaves and small branches on fire in less than 20 minutes. The smaller branches could then act as kindling for larger ones. Good points about water and ice, though. I'm curious now to see the assumptions in the old models. How much fiery molten rock raining from the sky does it take to melt and evaporate a heavy layer of snow?
Agreed, kindling would easily set on fire, and assuming a heavy density it could certainly start a forest fire. However, the effect would be no different than dropping a cigarette. When you get to that hair-trigger it's going to happen anyway. I assume the disaster is in the 'global' forest fire that would have ensued, keeping temperatures higher than habitable in major areas of the planet and then producing a cooling effect due to the soot emitted.
However, from my experience soot is emitted more by poor burning not good burning, so could the soot layer that was laid down have been made by a big poor-burn of fuel, rather than a major forest fire. I've seen people burning damp leaves and it emits huge plumes of soot.
How come the researchers don't research the possibility that the soot coughed up by the asteroid impact blocked light from reaching Earth and led to drastic cooling? Temperatures in the dinosaur days were pretty high relative to now, so it doesn't seem far fetched to me that they died of cold, and not heat. This theory also explains why smaller animals survived, especially mammals (hair is a good insulator).
The cooling effect is more possible and can also account for extinctions in the oceans as well. After the Krakatoa eruption for years the world had a cooler climate.
I've had plenty of camp fires in my time, and fresh wood certainly takes its time before combustion. I have serious doubts that a living tree would be capable of spontaneous ignition within 20 minutes of exposure to heat.
It may have ignighted forest fires in some dry or drought areas, but you're unlikely to spread forest fires in the boreal forests, where wildfires would have had the greatest effect. Forest fires in these regions happen only every 20-200 years, it's unlikely the raise of temperature in these regions would have caused a wildfire in the height of summer if it wasn't reaching one of these periods anyway. If the impact occurred during the winter months you'd have no chance to cause wildfires in these regions, even if the planetary temperature jumped by 260 degrees, the boreal regions would likely still be 20-30 degrees below the ignition point of wood. Considering these places can be 10+ feet deep in snow and ice (which incidentally insulate from heat) there likely wouldn't have been a noticeable effect.
Considering winter in the boreal lasts 5-6 months, there was a 50/50 chance that the impact would only have a negligible effect. Then consider the fact that the boreal has a high density of bogs and lakes means the wood is frequently waterlogged, so the chance of boreal wildfires being ignited gradually become slim-to-none, especially if it was a cold period in the climatic cycles.