[thedoc (OP)]

Mark Aalyson asked the Naked Scientists:
   
Presumably the carbon-based gases resulting from the oxidation of petroleum fuels are most responsible for today's climate change. I have been wondering, though, how much the actual heat of combustion of these fuels is boosting the earth's temperature. (Heat of combustion is, of course, the heat released in the chemical process of oxidation, i.e., burning.) Think of all the sun's radiant energy that has been stored over eons in the plants that decayed into petroleum now being released over the past couple of centuries as those fuels are burnt.

Thanks for your show!

Mark Aalyson


What do you think?

[chiralSPO]

There is a non-zero contribution here, but I would argue that it is insignificant compared to the effect of the carbon dioxide produced by burning said fuels.

Consider this: The average rate at which energy is being consumed by humanity is about 16 TW (1.6×10¹³ W)--let's assume that all of it is converted into heat. The average rate at which energy from the sun hits the Earth is about 100,000 TW (1×10¹⁷ W). So our burning of fossil fuels only increases the heat energy by 0.016 %.

Calculating the heat trapped by greenhouse effects is much more complicated, but having increased the atmospheric CO₂ from 280 ppm to 400 ppm means that roughly 1% more of the energy is retained...

[alancalverd]

The CO2 argument doesn't stand up to scrutiny, but the answer to the question is "yes". Everything every animal does, increases the temperature of the planet.

[chiralSPO]

Not sure what part of the CO₂ argument you are objecting to...

If it is my 1% number: Recent peer reviewed literature (Chem. Soc. Rev. 38, 25-35, for one) suggests that the increase in CO₂ levels since 1800 has decreased the thermal radiation of the Earth by about 1.6 W/m². Since the incoming solar radiation is about 100–200 W/m², and almost 100% of that is reflected or absorbed and re-emitted, that puts the order of magnitude at ~1%.

If you don't believe that CO₂ is a greenhouse gas, that's a different matter which probably deserves a new thread...

[Don_1]

I'm sure that the heat generated by man must have some effect on the Earths overall temperature, but it might be too small to measure. Winter temperatures in and around large cities, such as London, can often be a few degrees higher than the surrounding areas. And that is the point. This effect tends to be very localised. But, of course, heat rises and what effect the heat from London might be having on the UK temperatures in general might be almost impossible to evaluate.
Somehow, I don't think this effect would be significant, certainly nowhere near as significant as the effects of CO₂.