The correct answer is - the change of the total volume of water in the Earth's system.
The total volume of the water in the Earth's system is pretty much the same, and for it to change, and change the levels of the water in the oceans and seas, the Earth will have to go over a totally new conditions where either a new influx of water will reach our planet, or the heat will increase and the water will evaporate, for now that is not a possibility.
Having bright green feathers
if thats not the answer then maybe its
only hunting at night
Tropical places are hot because the humidity coming from the moisture of the plants and water are heated by the sun on the top layer of the tropical zone. The climate varies little in rain forest. There are five layers in the tropic trees so it's so thick that barely any light come through. This is also why vines grow up the trees so they can reach the sunlight to get nutrients. Also, the tropics are near the equator and that also causes the heat. The polars are cold because they barely get any sun heat to melt the snow or warm it up. The polars are melting due to certain chemicals and gasses in the atmosphere. also known as global warming. Hope that was helpful!