Answer :

this basically is because of 2 human activities:
1) deforestation-cutting down of trees 
2) carbon emmisions from burning fossil fuels and pollution from vehicle exhausts.

ways to reduce......
1)plant more trees
2)fit catalytic converter
manvirsaini96
DEFORESTATION,USE OF CFC, BURNING OF FOSSIL FUELS CAUSE GLOBAL WARMING,.
IT CAN BE REDUCED BY STOP CUTTING TREES, PREVENT USE OF CFC AND REDUCED USE OF CFC ( IT IS USED IN AEROSOL SPRAYS, DRY CLEANING, CAR SEATS, AC ,REFRIGERATERSS ETC.), USE CFC FREE PRODUCTS

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