Better scientific understanding of global warming makes the discussion about its geopolitical consequences increasingly urgent.
Put simply there are going to be winners and losers: hotter places and colder places – wetter places and drier places and yes places that disappear under the sea.
But the reality is a bit more complicated.
In particular are sea levels going up or down?
Yet to understand what is going on we first have to recognise that the Earth isn’t solid.
It started life as a ball of hot liquid about 4.5bn years ago and our planet has been cooling ever since.
Right at the centre of the Earth is a solid core of metal made of iron and nickel at a temperature of approximately 5,000C.
But this core is surrounded by an approximately 2,000km-thick ocean of molten metal – again mostly iron and nickel.
Surrounding this is a layer of rock called the mantle that is between 500C to 900C and at these red-hot temperatures the rock behaves like a solid over short periods of time (seconds – hours and days) but like a liquid over longer time periods (months to years) – so the rock flows even though it is not molten.
On top of the fluid mantle floats the crust – which is like the skin of the Earth.
It is a relatively thin layer of cool rock that is between 30 to 100km thick and contains all the mountains – forests – rivers – seas – continents – our world.
Since the crust is floating on the fluid mantle if you increase its weight by for instance building up kilometres of ice on top of it – then it sinks further into the mantle.
This is what has happened to the landmasses of Antarctica and Greenland – which are both covered in 2km to 3km of thick ice.
If global warming were to cause all that ice to melt then the sea level of the oceans would rise by more than 50 metres – submerging all the coastal cities of the world and making hundreds of millions of people homeless.
This seems obvious.
What is less obvious is how it might unfold.