There are 2 main causes of global warming:
- Natural causes: Natural disasters (earthquakes, volcanoes, natural forest fires,..)
- Human impact: 
  + Burninng fossil fuels: creates lots of carbon dioxide.
  + Deforestation: less CO2 is absorbed by trees.
  + Overpopulation
  + Ignorance: although we humans are playing a big part in the rise global warming, most of us are still ignorant, which is probably the biggest factor.
=> Human causes are much more significant

Effects:
- Sea level rise: due to the expansion of water and melting ice.
- Destroyed ecosystems
- Biodiversity loss: due to land degradation, deforestation and the warming of the sea.
- Pollution: human pollutants degrade the planet (E.g. The Great Smong of London)
...etc.