Does bonfire night in the UK increase temperature of the country / local area?
With numerous amounts of bonfires of a large size being created and knowing that forest fires in Australia can raise the temperature of the area there, is it feasible that the temperature of the UK slightly increases on bonfire night due to the amount of bonfires that have been lit or is the increase so infinitesimally small that it couldn't be measured let alone felt by the populace?
I doubt very much if the overall land area of the UK would be affected by the presence of an arbitrary number of bonfires. I have no idea of the number of bonfires, but let's do an estimation.
The population of the UK is around 60 million people.
Assume that the people most likely to light bonfires are in the 15 to 40 age group, UK Official Population Figures, produces a guessimate of 20 percent.
So you have possibly 12 million potential firestarters, let's cut that down to 6 million actually available to light fires, and that 100 people attend the event.
So you have 6000 large bonfires, (or a lot more smaller ones, it evens out) and say the area of each bonfire base is 10 square metres. So 6000 by 10 square metres is 60,000 square metres occupied by burning material. The total land area of the UK is 243.61 billion square metres. Actually that 6,000 is way too low but even 60,000 fires would still be ok in this rough estimation.
Enough already, I think.
I am ignoring calculating the heat output of each fire. A better way to estimate, in my opinion, is to consider if an average 5 degrees Celsius of 243.61 billion square metres of air will be affected in any detectable way by 60,000 square metres at an average temperature of say 600 degrees Celsius, (the average temperature of burning wood).
No, it won't, even if my number for fires is to 60,000 fires, which looking at it now seems a more likely figure. No matter what the fire number is, it still has to contend with 244 billion square metres of 5 degree Celsius air.
In addition we may have to allow for 2 to 5 million hot car exhausts and 3 million plus domestic heating house fires, which would have far more effect than bonfires.
So locally, within an radius of 200 metres of each fire, the air temperature increase is detectable, beyond that, no chance of detection seems likely.
A better way to think about it, after the fires all go out about two in the morning, is to ask yourself, will you notice a distinct change in the weather for the next day? Will all this energy affect you?
You could find out yourself, by looking at the weather pattern over London during the 1940/3 blitz, for example.
I put this part as the real answer, because I believe that rather than saying it depends on various factors, research can be carried to establish if this idea is true, by checking on weather patterns shortly after the fires and looking for correlations.
More supporting, (but indirect) evidence is the deadly smog that regularly covered London due to domestic coal fires, but it's far too complicated as regards the number of variables to easily establish correlations between the bonfire and the weather.
The focus then moves from PhysicsSE to EarthSciencesSE, imo.
Firewood produced 6190 BTU/lb. That's 14.4 MJ/kg. A 6" round log that is 2ft long should weigh about 10kg. That would give you 144MJ output, and probably lasts at least 4 hours, so let's say 36MJ per hour.
Sunlight produces about 1kw per square meter, at the UK's latitude that is about 600w per square meter. That's about 2.2 MJ per square meter in direct sunlight.
So if you placed a 4 meter by 4 meter grid across the entire UK and burned one of those logs in each grid square it would produce about as much heat energy as sunlight during the day. The UK is approximately 244 billion square meters so that would be about 15 billion burning logs.
With a population of 64 million, that means every man, woman, and child in the UK would have to burn 234 logs to produce that rise in temperature, say 10 degrees celsius difference between daily high/low temperature.
Say that 1/2 the population is involved, 20 people per bonfire, 20 logs per bonfire. That's 0.5 log-persons so maybe 1/400th the rise produced by sunlight in a day, or 0.025 degrees.
There can certainly be localized changes in temprature. Here in the US they use burn barrels or smudgepots in areas where the temperature rarely goes below freezing but a frost could ruin a crop.
I think the main effect is not the direct heat from bonfires, it is the release of particulates into the atmosphere, which then, unless it is windy, results in the condensation of a dense fog. My, perhaps mistaken, recollection is that there is almost always a fog on bonfire night unless the wind is blowing.
A fog will tend to keep the temperature at ground level higher than it would be under clear skies, since infrared radiation from the ground does not directly escape into space and radiation from low cloud heats the ground. Whether it feels warmer is a different matter, since fog increases the thermal conductivity of the air, making it feel colder.