The over-hunting of sardines has caused higher levels of phytoplankton in the ocean. While living, phytoplankton release oxygen into the atmosphere and use Carbon for photosynthesis.
When they die, their decay releases large amounts of methane and the poisonous gas, hydrogen sulfide. It also uses large amounts of oxygen. Methane is 21 times more effective than carbon dioxide in maintaining heat in the atmosphere.This results in the deaths of numerous marine animals.
Effects of global warming
• More carbon dioxide -> increase in plant growth.
• The increase in temperature -> rise in sea level from melting glaciers and polar ice caps (adds 0.2 mm annually)
• Rising temperatures will also cause drier conditions in many important agricultural regions.