The mass of the Earth is big enough that the gravitational force it creates can pull the hard shape of ice, rock and metal into a sphere.
NASA Earth Observatory images by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NASA's Goddard Space Flight Center
Imagine the Earth pulling everything it is made up of, all of its mass, towards its centre. This happens evenly all over the Earth, causing it to take on a round shape.
Tropical forests in the Congo for example have exceptionally high animal and plant species.
Forests and savannas are expected to be strongly affected in the coming decades by changing rainfall patterns. But land use will also have a major impact.
‘Tropics’ may conjure images of sun-kissed islands, but the expanding tropical zone could bring drought and cyclones further south.
The global tropical climate zone is expanding. At the current rate, by 2100 its edge will stretch from Sydney to Perth.
The Tropic of Capricorn sign in Namibia. Expansion of the tropics will have huge implications for people and nature.
The tropics are expanding at an unprecedented rate. This will have massive implications for societies, economies and the natural world.