What are the effects on global food webs if the sun's energy could no longer reach Earth

They would collapse as the sun gives the producers energy to grow i. e plants through photosynthesis. Without plants most animals would die out unless humans could somehow create a food in labs without animals or plants for 6 billion people. Ultimately it would be the death of the human race and just about everything on Earth apart from some plants that live in the deep depths of the sea which have adapted to not having as much sunlight.