The cold weather would kill crops in all but probably tropical latitudes. The lack of sunlight will slow plant growth. Placing plants in greenhouses / growhouses would keep them warm and you could supplement sunlight with LED lighting to feed the plants.

But creating enough greenhouse capacity to feed 8 billion people would be incredibly difficult. Bottom line would be, if something causes sunlight to be largely blocked around the world for a sustained period of time, the number of people who would starve to death would likely number in the billions.

LED lighting could also be used for outdoor crops. From my perspective green houses are most beneficial for pest management and water conservation. They might actually prevent light from reaching plants to the same degree as an outdoor grow due to reflection and opacity.

Greenhouses cool down rapidly after sunset though, they still freeze if it's many deg below freezing outside. (Also mass crops like wheat and soy would have to solve harvesting machinery and resource cost vs area size)

>Greenhouses cool down rapidly after sunset though

This simply isn't true and depends on a number of factors. greenhouses can fairly easily maintain 2-30 degrees above the outside temperature. furthermore, the temperature drop described in the article was 1-2 degrees below average.

Growhouses handle the situation perfectly well, but there are very few of them as conpared to open fields.

The only country i know of that has enough glasshouses to feed a significant chunk of its population is the netherlands.

Lava flows are a relatively local and immediate problem, what will really get large numbers of people over a long period of time is clouds of ash blocking out the sun.