People are vulnerable when they face risks (including from climate change) but can’t easily cope or adapt. Those most dependent upon weather patterns are liable to be most climate vulnerable, but gender, social status, poverty, power, access to and control over resources in the household, community and society are all determining factors. These multiple dimensions interact, so analysis and understanding needs to be two-fold: both interdisciplinary and intersectional.Conflict, fragility, widening inequalities and food insecurity — all compounded by climate change — are making millions more vulnerable. So the SDGs’ focus on ‘development and security for the furthest behind first’ makes addressing the climate risks faced by extremely vulnerable people a top priority. Ireland has a strong reputation for delivering development assistance for the poorest and most vulnerable, and using vulnerability as a framework for understanding and addressing the stresses and processes that fundamentally alter people’s wellbeing fits within Irish Aid’s ‘resilience approach’, set out in A Better World.Like social vulnerability, climate vulnerability is hard to recognise and to understand. Socioeconomic marginalisation, displacement and migration, neglected ill health, and uneven climatic monitoring and forecasting all systematically bias our understanding of climate risks: we tend to overlook the views and situations of marginalised people.Socially just governmental action on climate change adaptation should aim to eradicate extreme climate vulnerability. That requires recognising who experiences extreme vulnerability and understanding why; then including vulnerable people in processes fostering greater resilience, and allocating resources and creating opportunities for redistributive impact.Reaching Ireland’s policy objective of reducing humanitarian need means that development interventions will have to pre-empt and prepare for climate-related crises in ways that protect the most vulnerable and at risk. This key sheet focuses on how climate action can effectively support people in extreme vulnerability to reduce climate risks as much as possible.