Bikes, sure I used to commute 25 km each way to work 4 days a week, 8 months of the year for about 15 years, body does not allow that any longer so only 2-3 times a week and only 6 months of year.

However, the human body is only 20% efficient, thats why we heat and sweat while exercising(same as a car engine, we need cooling to remove excess energy). While commuting, I need at least 2 showers a day, plus I wash more cloths, plus I eat about 1000 calories more per day than normal. So to be honest I don't know if biking is that much more environmental friendly. I even have bike tires with metal studds to handle the ice.

Solar, yes it has to come but the problem still is that the manufacturing and refining processes are so energy demanding that solar cells have to generate electricity for 10-20 years before coming net energy producers. As we know very few things last that long so still solar is only marginal at best in terms of being a net energy producer.

Energy is and will be the thougest challenge for us going forward

Gan, global warming is obviously a concern and is very complicated with lots of contributing factors, there are actualy gases(SF6, used in some electronic applications) that are more than 10,000 times more active than CO2 as greenhouse gas. My personal take is that we will run out of fossile fuels long befoe global warming actually causes problems, if at all. Naturally the globe is in a long term cooling period and global warming so far has only helped avoiding the cooling which otherwise would have happened. The bottom line is that we have pumped so much CO2 into the atmosphere for so long and the effect to date are minimal. Is there a dangerous threshold, colud be I don't know, lets hope not because reality is that humanity will continue to generate CO2