It is Earth day, so I started thinking about the theoretical physics problems that could help reduce greenhouse-gas emissions and fight climate change.
We actually have a reasonable range of ways to generate energy without fossil fuels. The problem is, however, that the energy is generated by large immovable plants and that these plants cannot be just switched on and off at our convenience. This is quite unlike fossil fuels, which can be ignited and put out very quickly, and which also have a very high energy density so that they can be just carried around by various vehicles as an energy source.
For example, this means that renewable sources such as solar or wind, which output unevenly throughout the year or even the day, often have to be backed and strongly assisted by fossil fuels either way. On the other hand, nuclear fission reactors really cannot be turned off for the few hours of electricity usage dips during the day and night. Things such as pumping water up dams at some loss then have to be done with the energy surplus. This so-called pumped-storage hydroelectricity seems to be a reasonable solution to even out the electricity demand but its availability may depend on geography and a number of other factors. Either way, we still need an energy source for vehicles.
It seems that the most realistic option is to replace fossil fuels in vehicles by batteries that are charged through an electric grid. These should then power our vehicles and also possibly assist with the fluctuations of electricity needs during the day. However, there is a number of challenges. Batteries currently do not have the same energy density as fossil fuels and they tend to be relatively short-lived. For instance, commercial airliners will never go electric with current technology because the batteries are simply too heavy. Batteries also require rare materials and elements to be built.
I believe that most of the development of new batteries is on the side of engineering or experimental physics. However, are there any theoretical-physics problems that stand in the way? Is there a problem in theoretical physics whose solution would allow to make batteries lighter, simpler to make, and/or long-lived? Are there promising lines of theoretical research in this direction?