Cars are controversial. This sounds less radical now than when I was growing up in the '60s and '70s, when car ownership was part of the American Dream. There are so many reasons that cars are problematic. I won't go into them here, well, at least not most of them.
But all this reminds me of a presentation my students gave the other day. They were talking about solar energy, which they claimed had about a 20% efficiency rate. This didn't sound half bad to me. After all, solar energy is emission-free and relatively low-impact. If you compare it to the efficiency of the internal combustion engine (about 5% of that energy is transferred from your gallon of gas to the wheels of your car) it's an incredibly effective way of capturing light energy.
During the Q & A after the presentation I thought there was a pretty good "teachable moment." Last semester we learned about photosynthesis. With all the discussion of the internal workings of the chloroplast I didn't have a chance to discuss energy efficiency with my students. But here was my chance. Internal combustion motor, approximately 5%. Solar power generators, approximately 20%. Photosynthesis? About 33% efficiency.
How does this translate? About 33% of all the light that hits the leaf goes into the production of sugars that build the plant body (cellulose) or fuel the respiratory process (glucose). Pretty amazing way plants have evolved to utilize sunlight.