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? The answer seems clear when you consider that Antarctica has lost 3 trillion tonnes of ice in the last 25 years.
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.
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