1. Far fewer people subsistence farm so they're not one bad harvest away from famine 2. Not all areas would have complete crop failure; IIRC in 1816 "America's Breadbasket" (such as it was at that time) had a relatively easier time of it 3. We have a much better system of distributing information now and easy ways to transport seeds/cuttings. We could probably replace some of the lost crops with alternatives that were cold-tolerant or needed less sunlight if we knew what was coming. In 1816 even if you had a cold-tolerant grain variety there were fewer avenues to inform farmers and get them the seeds. 4. We also understand how to grow mushrooms at scale and farm fish at scale. 5. We have industrial processes. The capability to synthesize food here is probably far less than people assume (a lot of feedstock comes from the food industry) but it would help some. 6. We have TBMs capable of creating a vast network of underground tunnels where it would stay warmer and avoid freezing; doing this by hand would take many years. 7. In a worst-case scenario where billions would be expected to die: we can say "fuck it" and build a vast array of nuclear power plants to provide artificial light in tunnel or vertical farm operations. This would normally be a huge waste of resources when sunlight is plentiful. 8. We have satellites and much better weather forecasting abilities, plus a reasonable understanding of vulcanism. Unlike 1815 if we saw an eruption like this today we would know that the next few summers were going to be cold and crops would be at risk. We could immediately begin canning and preserving the huge quantities of food that normally get thrown out, used as cattle feed, processed into ethanol, etc.

There wouldn't be a silver bullet. We'd need a combination of techniques and less developed countries would probably bear the brunt of the suffering.

It is also possible the huge and growing moron class would buy food and throw it away just to thumb their nose at "da gubbmit fer tryin' to tell meh what tado", and politicians would claim the jury is still out on this "climate" stuff, then we end up with a global catastrophe despite possessing the resources to prevent it. After all: we are perfectly capable of feeding everyone alive right now but we don't, not even in a first-world country like the USA.

We also have a staggering amount of food already canned/frozen or grown in greenhouses just to make sure staple foods are available year-round.

Thanks to plastic, greenhouses are cheap and easy to make, so even poorer countries would fare reasonably well. What is harder to predict is how well greenhouses already in colder climates would fare.

I completely agree with everything that you said above but doubt that people will continue to be entrenched in their ideas when people start dying from starvation locally and not in a foreign land that they can ignore.

The world is much richer overall and food production per capita is probably much higher. The world is much better connected, both in information (winter is coming!) and flow of goods. There would be far less hunger, although in a capitalist world people on the margin would still get squeezed.

Also, a few years of cooling might counteract global warming a little, although this would probably end up just giving more fuel to the "keep calm and burn coal" camp. Not much point in installing solar panels when the sky is dark.

Flow of goods can also spread the pain, no region is spared. Reliable agriculture with better efficiency means overproduction doesn't happen as much, so there's less cushion. Rome was better at shipping cheaply than previous societies, and better integrated, so it suffered much more widespread (although less frequent) famines that could affect nearly the whole empire.