What is the one single most important reason that human impact on the planet has been so great?

Increasing population

Explanation:

As we can see that the death rate is decreasing while at the same time the birth rate is increasing due to which it increased the population that directly impact the planet so great

Day by day the population of the villages, cities, states, the country is increasing which would create a direct human impact on the planet  

Therefore the increasing population is the one and single most important reason

co2reflects heat radiation back to earth buning coal and oil emits co2 globe warms