Why are the number of green sea turtles decreasing?

Green sea turtles are dying because of many differing factors.

these factors are

Global warming.

Green sea turtles are very sensitive to hot and cold weathers. Baby turtles could die as they hatch from the heat of the sun if they dont make it to the water.

Predators

Predators include foxes, racoons, seabirds as a baby. and sharks prey when they are matured and enter the sea.

Pathogens and diseases

Pathogens and diseases can arise from virtually anything. Malnutritions, Pollution in the waters. eg, oil, salinity.

these are some answers

There is absolutely no evidence whatsoever that "global warming " has had any effect on populations of sea turtles. Biggest threat to sea turtle populations, as far as humans are concerned, are dying in nets of longline fishing trawlers.