Does heat from friction contribute to global warming?  

Earth’s atmosphere is heating up faster than predicted by climate change models (e. g. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082062).  Those models assume that greenhouse gas accumulation is the sole cause of global warming (https://aiche.onlinelibrary.wiley.com/doi/full/10.1002/ep.13041; https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/2269/1684).  

The discrepancy between predictions and reality raises the question:  are greenhouse gases really the only cause of global warming?  There may be at least one additional, important and as yet unrecognized contributing factor:  our old thermodynamic friend, the law of conservation of energy.  Or, in more simplistic terms, heat from friction.  

Obviously, combustion of fossil fuels creates heat, but climate change researchers consider this inconsequential relative to the greenhouse effect (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2015GL063514).  

The role of heat from friction hasn’t previously been considered.  The first law of thermodynamics dictates that the energy used to propel and stop vehicles will eventually be converted to heat.  

At least two sources of anthropogenic frictional heat may be significant contributors to climate change.  One is aircraft.  Airliners cruise pan-globally at high subsonic speeds.  Right now there are roughly 10,000+ planes airborne.  How many contrails can you see right now?  

Commercial jet aircraft cruise in the lower stratosphere.  How much does frictional heat add to heat from jet fuel combustion?  Does direct heating of the atmosphere at this level somehow accentuate the greenhouse effect or otherwise magnify tropospheric heating?  These are speculations, but the point is, thermal effects of aircraft haven’t been excluded as causative factors to global warming.  

An even more significant source of frictional heat may be brakes.  Brakes use friction to decelerate and stop wheeled vehicles:  bikes, cars, trucks, trains, even landing aircraft.  In doing so, the vehicle’s kinetic energy is converted to heat.  Depending on frequency and duration of braking, discs reach temperatures of 200 – 600°C.  (Please never touch a brake disc on a vehicle shortly after it’s stopped!)  

There are well over a billion cars on the planet.  How many times per day do you use your brakes?  Without doing the detailed math, you get the idea:  brakes put a lot of heat into the atmosphere!  

Consider stopping a 10,000 metric ton train travelling at 20 m / s.  Remember conservation of energy:  the moving train’s kinetic energy equals 2000 MJ.  All of this gets converted to heat during stopping.  Also, since most vehicular braking occurs in large urban areas, this heat source would be concentrated in those areas.  

So what to do?  First, the above concepts may deserve more thorough investigation than this cursory analysis.  Findings may support more attention to boundary layer physics and streamlining of vehicles, especially aircraft.  

Even without further investigation, the above observations support much wider use of regenerative braking systems (https://www.nature.com/articles/129864a0).  Regenerative brakes convert a vehicle’s kinetic energy into other more useful forms of energy than heat.  That recovered energy can then be re-used to propel the vehicle, which reduces need for energy from fossil fuel combustion.  Therefore, regenerative brakes conceivably decrease global warming by at least two mechanisms:  reduced heat from brake friction and reduced greenhouse gas production.