More Economist bashing. Reasoning from false premises gives false results.

Fertiliser, which has enabled the world to generate enormous growth in agricultural output, is largely produced from petroleum. This seems to place a long-term constraint on food output, absent some new innovation.

Nitrogen fertilizer is produced from methane, not petroleum, but that's not the first or only way to do it. Methane is just a convenient and still relatively cheap source of hydrogen - CH4 - and that is useful for making ammonia - NH3.

Water is also a source - H2O. Though not as rich it is certainly abundant compared to methane. That's one of Mother Nature's favorite methods. There are many ways to make hydrogen, none as cheap as methane at current prices, but that seems set to change.

It takes energy to make hydrogen from water. Mother Nature uses lightning. One recent suggestion is to use wind power, which is intermittent, but that doesn't matter when the energy is "stored" as hydrogen, or better yet, ammonia. Another suggestion is to use geothermal energy, especially in remote places such as Iceland that has it in abundance, but no good use for it. It can also be made from biomass, it is a byproduct of pyrolysis. There's a certain elegance to that method since the fertilizer would be used to grow more biomass.

Secondly, expanded agricultural output, especially in a place like Brazil, will likely mean deforestation. Forests are valuable carbon sinks, and so an increase in cultivated land could exacerbate climate change, reducing the long-term productive potential of the world's farms.

No, it won't likely mean deforestation. The greatest growth in Brazilian ag land is in the vast semi-arid cerrado, which is only 1/3 cultivated as yet. In the past it wasn't possible, but new technologies have made it bloom. The same sorts of land in Africa and other S. American countries are also ripe for development - no forests need be harmed.

Forests may be harmed, but it isn't due to the requirements of agriculture. It isn't necessary. This is a political issue. Will it be allowed or not? It would become less feasible politically if ding bat journalists stopped insisting that it was the only way to increase the extent of cultivated land.

Given these constraints, what is the optimal long-term solution? A global carbon price would clearly be ideal, but is also unlikely. Should developed nations heavily tax their beef cattle?

There's nothing ideal about a global carbon tax. That's like giving guns to children. All of that money in the hands of irresponsible politicians and bureaucrats? Some ideal! Besides, it wouldn't do diddly to relieve a food crunch. How did this non-sequitur end up in the discussion? Oh, right, the unnecessary forest clearing gaffe. No article or blog post is complete without genuflecting to the carbon tax gods.

One ding bat tax deserves another, so tax cattle too. But why? They eat grain. That makes sense - not. They don't need grain. Grass is all that is required, and in some of the places where they are raised in great numbers, such as S. America, that's how they are raised. Chickens and pigs, OTOH, can't survive on grass. They need rich foods such as grain, just like people.

We need better educated economists.