This paper focuses on 'autonomous adaptation' and has one aim. It assesses the economic consequences of the failure effects of autonomous adaptation in response to extreme flood events. The study found that Bangladeshi farmers are highly resilient to extreme flood events, but the economic consequences of failure effects of autonomous crop adaptation on marginal farmers are large. The failure effects are defined as total input costs plus the small profit (otherwise) made from selling the small surplus remaining from subsistence needs. The total input costs increase with the number of flood events in the studied area. Total agricultural cost includes cost of seedlings, fertilizer, pesticides, land preparation, human labour and watering. The paper concludes that the economic loss accelerates food insecurity and could ultimately lead to human insecurity in Bangladesh, which could be exacerbated by the effects of climate change.