I used to worry about this as an existential risk, especially after I internalised James Hansen's paper pointing out that climate change causes increasing dispersion of the PDF of weather deviation from climatic average as well as changes in location of climatic average.[1]

Simplified, possibly too much: the "bell-shaped curve" of, say, temperature, is becoming lower and broader as well as moving to the right. (Same change for other climate variables.)

This means that formerly rare extreme climate events, like simultaneous drought in two or more of the world's large grain-growing ragions, become much less rare, much sooner than would be the case if dispersion did not increase.

However: there is a lot of "fat" in modern food production.

Enormous quantities of maize, palm oil, and sugar cane are grown for biofuels (causing erosion, soil poisoning, and depletion of aquifers by the way). I believe the majority of the US maize crop is used for this, and a major fraction of Brazilian sugar cane also. Further enormous quantities of maize, soy, and wheat are grown to feed meat animals - cows, pigs, chickens.

When multi-regional[2] crop failure hits, we eat the animals and then their grain. That would get us through five or so growing seasons, unless every grain-growing region is affected, and it's extremely unlikely that a multiple simultaneous drought event lasts that long.

In addition, there is a transition under way from internal-combustion engined transport to electric, so the demand for biofuels should decrease over the next few decades, giving us more of an arable land buffer.

And the food growing system is not fixed. New heat and drought-resistant varieties are being developed in response to changes in climate. Irrigation improvements are being made. There is stuff that's further out that would make big improvements: experiments in artificial meat, for example. If that takes off, we'll be able to take more land out of production in 50 years or so, when it scales up sufficiently. And so on.

So the famine danger of multi-regional simultaneous drought is not existential. I'd like to think no-one is going to launch the nukes because they can't get steak or cauliflower, so I don't think the danger is even civilisational.[3]

To me, bigger dangers are those I listed above: loss of usable top soil, poisoning of the remaining top soil in various ways, and aquifer depletion. There could be a tipping point in soil ecosystems. We don't know.

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1. I think this was the paper that started me worrying: https://pubs.giss.nasa.gov/abs/ha05510d.html

2. The regions that really matter for global food supply are North America (US Midwest, southern Canada plains), the North China Plain, Europe (France through Ukraine and western Russia), North India, southern Brazil and Argentina, and Indonesia-Philippines-South-East Asia. Possibly parts of east Africa.

Grains (wheat, maize, rice, soy, barley, and other (sorghum, oats, rye, millet mainly)) are the crops that matter.

3. The current famine in Madagascar is entirely political, as has been the case with all famines since the Great Famine in Ireland, and the famines in British India before that. There was enough food globally, and enough transport to get it where it was needed; politicians got in the way. Europe and the US could feed Madagascar and not even notice.)