Do you have any references to back up these claims?
For the meat (not saying you should consume a meat based diet but rather one that's mostly plants that properly incorporates meat as necessary... i.e., a traditional diet): https://link.springer.com/article/10.1007/s10669-015-9577-y .
Also, as an aside, if you don't want to turn veggie farming into mining with some extra steps, you need to raise animals that you can grind up into fertilizer. Otherwise, you have to mine petrochemicals or bat poop, which is extremely bad for the environment.
Is the article asserting that they can feed the world this way? Also the word climate didn't appear in the article either but I might have forgotten in the few hours since I read it. I saw the story more as a calorie supplement like a victory garden in WW2.
I garden in a small space like the article quite a bit as well and find that worm compost from cooking scraps is sufficient for keeping my soil healthy without specially purchased fertilizer. I imagine most households have quite a bit of organic waste products produced from groceries and could support a modest garden in their yards too.
Your home garden is not intensively cultivated the way most farmland is.
Yes, more people should garden. No one should think it's the end-all answer to our food problems, or even that it's going to make a huge difference. Still good to know where your food came from and some stuff tastes better.
Basically the answer is a long growing season: getting 3 rounds of crops out of the same field each season, and keeping the dirt rich by collecting everyone's "night buckets" and preparing the hu-manure to turn nutrients back into the soil.
My impression is that growing produce and composting organic matter can produce more calories per acre than industrial farming methods, but the cost is labor, selling vegetables is only profitable with the petro-fertilizer methods.
Additionally, the study is using the USDA guidelines in their model scenarios. Those guidelines are heavily influenced by food lobbyists and are not entirely in line with what sustainability advocates have been pushing. For example, the emissions assumptions made in that paper are assuming that the replacement calories are coming from our "traditional" food system and they are not modeling in any increase in local production. i.e. replacing a chicken breast from Iowa with a bag of Apples from Chile might indeed be a net negative in terms of emissions. But that is not what food advocates are pushing for. It is more like: replace a steak with a head of broccoli from your local CSA. That would likely be very net positive in terms of emissions.
Except the brocolli is less nutritious and less caloric than the steak. 8oz of steak is more calorie dense and is a form of complete nutrition, whereas a head of brocolli gives you a very tiny amount of calories, some fiber, and a lot of vitamin C. It's missing vital nutrition. Growing enough brocolli to make up for the missing calories is quite environmentally taxing, and consuming enough brocolli to make up for the steak would be sickening.
You linked to a study that critiques USDA guidelines, which has nothing to do with the changes that sustainability advocates are pushing for. And now you are picking apart a short internet comment analogy to try to make the case that beef consumption is a good thing. The fact is, beef is one of the highest emissions foods per calorie that a person can eat. Until you directly address that argument, you should stop "encouraging more meat consumption" (from your top comment).