How can global warming be controlled?

$A$ large number of fish suddenly die in a lake near a village. Which of the following could be the reason for this?
$(a)$ Excessive use of urea and phosphate fertilizers in nearby fields.
$(b)$ Spraying of $DDT$ in the entire area.
$(c)$ The lake water has turned green and murky.
$(d)$ The population of phytoplankton in the lake has decreased,reducing the photosynthetic capacity.
Which two of the above reasons are responsible?

Chipko movement was launched for the protection of

Aerosols reduce primary productivity by

Where was the $UN$ Climate Change Conference held in $2012$?

Increase in concentration of a toxicant at successive trophic levels is called