The highest population growth now is in the poorest countries, and even that is slowing as economic conditions improve. At least for people. First, Price slights nuclear energy. This could be increased by a factor of 60 to 100 by using breeder reactors, and this would also reduce the problem of long term nuclear waste storage. And of course there is a lot of uranium that has not yet been mined.
Price completely dismisses fusion.
It is not currently practical, but has enormous potential. He says little about conservation. But as recently as two generations ago people lived using a lot less energy, and they can again. Some new technologies can reduce energy use dramatically. Consider information transmission, surely an important factor in the future.