Climate change is a clear and present danger that has already claimed the lives of millions, and is set to claim millions more - in every single country across the globe.
Islands will - and have - been wiped out, hundreds of millions will be made homeless, disease and starvation will kill countless millions, and everyone will suffer.
There will be three types of countries: wealthy ones who can help all their citizens through the worst effects (if they choose to), poorer nations that will lose citizens and cities to gradual and unforeseen disasters, and countries which will cease to exist.
In 2100, as things currently stand, the world will be 3°C warmer than pre-industrial levels, according to the United Nations (UN).
If no action is taken, cities like Miami, Ho Chi Minh City, and Shanghai will be entirely submerged - but at least they have governments that can spend billions of pounds to save them by building flood defence walls, reclaiming land, and relocating citizens when needed.
The worst-affected countries don't have that luxury, and need our help urgently. We've explained our methodology below for working out which nations are most vulnerable - even though all countries will suffer as a result of climate change.
Four of the countries set to be worst affected by climate change are in this region The US Navy has a base on Marshall Islands' Kwajalein Atoll Pohnpei is one of many islands in the FSM under threat from rising sea levels