We need to do this in the UK. There are many urban roof tops that could be used to grow food where it is needed.
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In the coming years the effects of global heating will have an impact on food supply. The impending crisis in the UK shows that we must have a stronger and more resilient local food supply. Conventional agriculture takes time to switch to growing different crops, but roof top gardens could be up and running within weeks.
What is likely to stop that? Local planners and health and safety concerns! I am not saying that we should ignore the safety implications of roof top gardens but