How can sea level rise because of air pollution and what will it cause for people living there near seas?

To put it in very "simple" terms

more pollution = traps more heat in the atmosphere coming from the sun

more heat = warmer temperatures

warmer temperatures = melting glaciers/ice that would normally stay as ice all year round

melting ice = more water in ocean

more water = higher sea level

higher sea level = flooding in coastal areas

if flooding is high enough, pretty much reduced space on islands and thus extreme crowding or displaced people thus meaning a refugee crisis