Global warming is caused by the greenhouse effect—and things that we as humans are doing to exacerbate this effect.
The more carbon dioxide that is released into the atmosphere, the more serious the greenhouse effect becomes. Things that cause more carbon dioxide to be released include the burning of fossil fuels, which takes place in the production of electricity and every time someone drives an ordinary car. Other vehicles, like motorbikes and airplanes, also contribute to this.
Trees help to reduce the greenhouse effect and global warming by using the carbon dioxide in the atmosphere to make oxygen. Due to that, deforestation is another cause of global warming, because with fewer trees, there is more carbon dioxide.
Another gas which contributes to global warming is methane, which is emitted by trash in landfills. So, the wastefulness of humans and a shortage of recycling programs around the world is another cause of global warming.