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Comment by swader999 | Hacker News Reader

Doesn't yield increase with more CO2? It certainly did in my greenhouse when I put my large rabbit inside.

Yield yes, but not nutritional contents. Most vital nutrients require more than just CO2 to have more production in a plant (notably, Nitrogen is needed).

Nitrogen is 70% of the atmosphere, I don’t see any way for it to run short until the death of the sun (or the use of von Neumann probes) boils off Earth’s atmosphere.

If you’re going to worry about fertilisers, worry about phosphate and potassium… but even then, the problem and solution is unrelated to greenhouse gases.

Nitrogen is 70% of the atmosphere but unlike CO2 it's concentration isn't going up in an appreciable way. So if a plant is constraint in nutrients by Nitrogen, it can't make more of those if CO2 goes up. If CO2 goes up it can only make things that require more Carbon and Oxygen, both of which only form very basic structures the plants can use to build. Not nutrients.

That assumes the plants get it directly from the air. Legumes do (hence the invention of crop rotation), but most plants get it from fertilisers, the manufacturers of which get it from the air and can scale up independently of the farms. The manufacturing process currently uses methane… but only because that’s historically been the cheapest source of hydrogen.

That still leaves getting it on the field. Overfertilization is a problem and as mentioned, the plant will require that Nitrogen in proportion to the amount of CO2 to even begin to compensate the lack of Nitrogen. With CO2 being 50% higher that means you'd already have to fertilize 50% more to get the same Nitrogen to CO2 ratio as preindustrial levels. And that number isn't going to get better anytime soon. I don't think that adding 50% fertilizer on top of the current fertilization is a solution, overfertilization already causes way to many problems. I've had to stay of the tap water more than once as a child because a farmer didn't follow the fertilization limits.

> That still leaves getting it on the field.

This is a solved problem since the invention of the bucket and pointy stick, when “fertiliser” meant “manure”.

> With CO2 being 50% higher that means you'd already have to fertilize 50% more to get the same Nitrogen to CO2 ratio as preindustrial levels.

Why do you want to match the air rather than the plant’s actual growth? Plants are limited by a lot of different factors, so while CO2 helps a bit, doubling it doesn’t double the nitrogen use all by itself.

> a farmer didn't follow the fertilization limits

While this is a real issue, there are many solutions, and worrying about CO2 altering crop yields isn’t one of them.

Not directly, no. But crop yields vary wildly with temperature and temperature is changing on account of CO2.

Absolutely. Thanks for your other comment, I shared a belief with @swader999 that the world was greening, it’s useful that you suggested an alternative hypothesis.

https://news.ycombinator.com/item?id=31643970

Overfertilization is a major issue, there is only so much fertilizer you can put on the field without making next years harvest impossible due to oversalting or damaging root systems. And you can bet farmers are already maxing that out as much as they can on an industrial scale.

> Overfertilization is a major issue

An unrelated issue. That’s important. I have no reason to expect it to get worse. What runs off the fields is necessarily not used by crops.

> And you can bet farmers are already maxing that out as much as they can on an industrial scale.

I doubt that.

All industries, agriculture included, are incentivised to maximise profits. Optimising profit sure isn’t environmentally friendly, but it also doesn’t mean treating fertiliser as a magic potion.

A productivity optimised farm looks like this: https://farmingaquaponics.com/aeroponics-vs-hydroponics/

That’s pointlessly expensive right now for most crops, so those are fairly limited. Likewise, the economically optimal quantity of fertiliser used by farms is different from the optimal quantity for the health of people living down-river — but that’s just as true regardless of if CO2 is higher or lower than we consider desirable for the general global climate.

Yes, but not faster than the total mass of crops drops due to the increase in heat. Crop yield per plant in a controlled environment where only CO2 is increased != total crop yield given all of the circumstances involved in climate change.

CO2 as a heat trap is the problem, not so much CO2 in the atmosphere as an input to plant and animal life.

Why is the planet becoming more green over the past three decades (per NASA observations) if there's a net loss?

You are well into 'just asking questions'[1] territory, something that really ticks me off because all of these are a google search away, but just for the record:

Replanting and more (and more intense) agriculture is what is making our planet greener. For the moment. But there are pretty clear upper limits to what the planet can deal with temperature wise, at some point it will get so hot that plants will not be able to retain their moisture. Already there are territories that were arable in the recent past that today are not or are subject to extreme droughts almost every summer.

For Europe the estimates are that Portugal (and Spain) are going to be the first to be hit really hard, and in a way that is already underway:

https://portuguese-american-journal.com/wildfires-severe-cli...

[1] https://rationalwiki.org/wiki/Just_asking_questions

Also the planet could well become greener with global warming but the issue is the rate of change. Even if the new growing conditions were great for some crops, evolving our entire agriculture and food regimen to them in a few decades is a huge ordeal.

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