I noticed that Pahan has provided you with a good structure
Ohh.... had I ? Lol
It is known that the vast amount of litter produced by mankind is considered to be the main cause of the climate woes, degeneration of maritime zones and environment. Many scientists are concerned how to cope with this problem reducing the number of refuse, albeit, very few of us are inclined to spare a thought to the causes of our actions.
Your writing is quite impressive.However, I like if you reduce the length of your sentences a bit more (e.g. the last sentence of your intro is a bit too long). Long sentence give more work to the reader as he needs to memorize things. The reader won't be happy to do that :D
From the point of my view, the majority of rubbish such as bottles and other non-biodegradable materials created by humankind can be seen on the surface of the oceans and seas.
Better you begin the body para with the reason. Your prompt asks you what are the possible causes for this situation. So, it's good you opened the para with the first reason.