The answer has a lot to do with addressing our energy challenges, if you want to take biofuels into account.
Plants are roughly 1% effective at converting sunlight to stored hydrocarbons (mostly cellulose). Sometimes we can bump that up by a factor of 2-3. Photovoltaics are much more effecitve, about 20% in production, with theoretical maximums of 40%, which translates to even higher with multi-layer cells. But that just gets you electricity, not storage.
Algae are roughly 10x more productive than plants in converting sunlight to biomass. Which is pretty useful. However where a farm is a pretty lightly engineered environment (provide irrigation, even tillage is optional these days), if you're going to grow algae, you've got to provide a hell of a lot of services plants otherwise self-service: support, pest control, nutrient transport, and the like. Yes, your primary productivity goes up 10x but your capital investments are even higher. I've followed the field from a distance, and most pilot projects have been abandoned.
So instead of harvesting protein from algae and yeast, we get them from acres of soybeans. It's just cheaper. And the technology is too expensive.
Population
Yes, growth rates have declined, but we're still dangerously over long-term sustainable levels. And unfortunately, it's poorer areas where kids are most prevalent. In advanced societies, children are a net cost, in poor ones, starting at an early age, they can help with household tasks and chores.
Let's look a bit closer at that: why?
The answer has a lot to do with addressing our energy challenges, if you want to take biofuels into account.
Plants are roughly 1% effective at converting sunlight to stored hydrocarbons (mostly cellulose). Sometimes we can bump that up by a factor of 2-3. Photovoltaics are much more effecitve, about 20% in production, with theoretical maximums of 40%, which translates to even higher with multi-layer cells. But that just gets you electricity, not storage.
Algae are roughly 10x more productive than plants in converting sunlight to biomass. Which is pretty useful. However where a farm is a pretty lightly engineered environment (provide irrigation, even tillage is optional these days), if you're going to grow algae, you've got to provide a hell of a lot of services plants otherwise self-service: support, pest control, nutrient transport, and the like. Yes, your primary productivity goes up 10x but your capital investments are even higher. I've followed the field from a distance, and most pilot projects have been abandoned.
So instead of harvesting protein from algae and yeast, we get them from acres of soybeans. It's just cheaper. And the technology is too expensive.
Population
Yes, growth rates have declined, but we're still dangerously over long-term sustainable levels. And unfortunately, it's poorer areas where kids are most prevalent. In advanced societies, children are a net cost, in poor ones, starting at an early age, they can help with household tasks and chores.