if the wattage will go down because of a better efficiency, then more miners will be added = the same result as today(with more hashpower, but same consumption), you can't escape from that equation
the only thing to reduce it would be that bitcoin will remain at current price(after the halving), therefore miners need to shut down 50% of the total hash, unless they manage to double their efficiency in 1 year
so there is a percentage of possibility that nothing will change with the reward(besides the difficulty), highly unlikely though
The total cost of mining is usually similar to the block rewards.
It is still cheaper than cost of maintaining today's banking system, many many folds.
then why governments are not adopting bitcoin, it would be a win win situation for them, if the cost are vastly cheaper, is only regualtion that prevent this? or there is something else...
i think they just don't like to not have the control over money
Well take america for example... We print money to cover debt. Which further increases inflation and the national debt, which we in turn print more money to cover. It's a vicious circle. But on that basis alone, america would be unable to adopt bitcoin as currency (with the inability to print it at will) without going completely bankrupt We don't want that along with every country that we do business with. Now like its been mentioned it's possible they backbone on the blockchain... this still doesn't eliminate USD and it wont.